Quorum Sensing Disruption in Vibrio harveyi Bacteria by Clay

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Clay Catalyzed Disruption of Quorum Sensing in Vibrio harveyi Bacteria Sajo Naik, Jonathon Scholin, San Ching, Fang Chi, and Marc Herpfer J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b03918 • Publication Date (Web): 12 Dec 2017 Downloaded from http://pubs.acs.org on December 21, 2017

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Journal of Agricultural and Food Chemistry

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Quorum Sensing Disruption in Vibrio harveyi

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Bacteria by Clay Materials

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Sajo P. Naik, * Jonathon Scholin, San Ching, Fang Chi, and Marc

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Herpfer

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The Oil-Dri Innovation Center

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777 Forest Edge Road

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Vernon Hills, IL 60061-3197

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Corresponding Author Sajo P. Naik The Oil-Dri Innovation Center 777 Forest Edge Road Vernon Hills, IL 60061-3197 [email protected] Phone: +1- 847-537-7543

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ABSTRACT

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This work describes the use of clay minerals as catalysts for the degradation of quorum sensing

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molecule, N-(3-Oxooctanoyl)-DL-homoserine lactone. Certain clay minerals due to their surface

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properties and porosity can catalytically degrade the quorum sensing molecule into smaller

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fragments. The disruption of quorum sensing by clay in a growing Gram-negative Vibrio harveyi

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bacteria culture was also studied by monitoring luminescence and population density of the

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bacteria, wherein quenching of bacterial quorum sensing activity was observed by means of

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luminescence reduction. The results of this study show that food grade clays can be used as

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biocatalysts in disrupting bacterial activity in various media.

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KEYWORDS

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Clay, Biocatalysis, Transformations, N- (3-Oxooctanoyl)-DL-homoserine, quorum sensing

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1. Introduction

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Quorum sensing is a cell-to-cell communicating system employed by bacteria to regulate

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bacterial activity in response to various stimuli. Quorum sensing was first reported in the study of

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a marine bacteria Vibrio fischeri which exhibited bioluminescence upon bacteria reaching a high

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population density [1]. Typically, bacteria biosynthesize distinctive chemicals including N-

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acylhomoserine lactones (AHLs) as quorum sensing signals; specifically, AHLs, such as N-(3-

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Oxooctanoyl)-DL-homoserine lactone are used by some Gram-negative bacteria in quorum

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sensing signaling. The biochemical production and effectiveness of AHLs depend primarily on

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the activity of Lux and LuxR protein families, respectively, which together with the quorum

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sensing molecules, constitute the overall quorum sensing signaling system. After AHLs are

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produced by Lux enzymes, they diffuse across bacterial membranes and accumulate in the

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surroundings until critical local concentrations are reached [2]. At a given threshold

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concentration, the AHL binds to LuxR response regulator, forming a complex that activates gene

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expression. Some bacterial features controlled through quorum sensing include bacteria

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population, antibiotic generation, bioluminescence, nitrogen-fixing gene regulation, Ti plasmid

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conjugal transfer, virulent gene expression, pigment generation, bacterial swarming, and biofilm

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formation [3].

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Quorum quenching is a process of disrupting the bacterial quorum system. Modulation of Lux,

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LuxR and deactivation of quorum quenching molecules are some ways of accomplishing quorum

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quenching. There exist several reports on the use of naturally occurring or artificially synthesized

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antagonists as possible quorum quenchers [4,7]. Ideally, quorum sensing quenchers, inhibitors,

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or regulators should not interfere with the normal physiological functions of bacterial cells or not

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prompt bacteria to develop resistance. Although several different methods of quorum quenching

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are reported, to the best of our knowledge there does not exist any biocatalytic ways involving

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solid acid catalysts such as clays to disrupt quorum sensing in bacteria.

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Clay minerals are hydrous aluminum phyllosilicates, which may contain variable

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amounts of iron, magnesium, alkali metals, alkaline earths and other cations. Clay minerals exist

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in nature but must be further processed or purified such that their chemical or physical properties

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required in various applications may be brought to the fore. Clays have a very interesting history

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as solid acid catalysts. Acid-treated clays were used as catalysts in petroleum refining in the early

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1930s [8-9]. However, their applicability was limited due to their lack of thermal stability under

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high temperature fluidized catalytic cracking (FCC) conditions. Consequently, clays were

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replaced by more stable synthetic catalysts, e.g. silica-alumina, zeolites, etc. in the petrochemical

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industry. Besides catalysis clay minerals have several other applications as adsorbents, feed

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additives, fillers, carriers, etc. [8-13]. In several animal health products, clay minerals are used as

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feed additives as they are non-toxic, have high porosity and presence of active sites that can bind

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a range of fungal and microbial toxins to improve the health of the animal [10-13]. In the animal

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feed and health industry versatility of clays to perform more than one physiological functions is

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desired.

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Herein, through in vitro studies we demonstrate that clays can adsorb and catalyze

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bacterial quorum sensing molecules to break them into smaller fragments in an aqueous system.

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We used N-(3 Oxooctanoyl)-DL-homoserine lactone, an AHL type quorum sensing molecule as

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a model quorum sensing molecule for this in vitro study. We followed up the in vitro study by

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directly monitoring the quorum quenching in Vibrio harveyi bacteria in the presence of clays

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under simulated bacterial growth conditions. Bioluminescence and bacteria population were the

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parameters employed to gauge the quorum sensing activity of the system. Clay minerals

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functioned as adsorption/catalytic antagonists in that the AHLs responsible for quorum sensing

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activity in some bacteria were either separated out by adsorption or were catalytically broken

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down by the active site in clay surface.

Reducing the concentration of quorum sensing

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molecules in the bacterial system either by physical separation or chemical transformation into

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non-active molecules using clays demonstrate possible way of disrupting quorum sensing in

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bacteria which could have a possible impact on controlling bacterial ability to produce toxins or

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virulence as such functions in bacteria are control through quorum sensing.

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2. Materials

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2.1 Clays and chemicals

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The clay samples were obtained from Amlan international/Oil-Dri corporation of America [13].

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Calibrin-A and Z are type of processed montmorillonite clays and their details have been

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described earlier [11, 12]. All the other chemicals were obtained from Sigma-Aldrich, USA and

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used as-received.

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3. Methods

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3.1 Clay Characterization

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Clays were characterized by X-ray diffraction (XRD) on a Bruker D2 Phaser instrument using

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Cukα as the X-ray source. A wet slide method of sample preparation was used for the analysis

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(Data not shown). A Quantachrome NOVA 4200 instrument was used to measure the total pore

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volume of Calibrin A and Calibrin Z samples by N2 adsorption/desorption method. The sample

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was degassed at 110 oC for 12 h under vacuum followed by nitrogen adsorption/desorption study

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at 77 K. Pore volume was estimated by Density Functional Theory (DFT) method of analysis

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using NovaWin 11.03. Specific surface areas of the materials were evaluated using Brunner

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Emmett Taylor (BET) method from N2 data.

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The acidity of the clay samples was measured on a Chemisorb 2720, Micromeritics instrument

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using ammonia as a probe molecule. Typically, 25–100 mg of the sample (100 mesh) was held

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between small lumps of inert quartz wool taken in a quartz tube. The sample tube was connected

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to the device and heated to 120oC, 12 h, to remove adsorbed water and other volatile impurities.

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After cooling to 25oC, dry ammonia gas [20 % NH3 balance He (UHP); 20 mL/min] was then

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passed over the sample for 15 minutes. The physically adsorbed ammonia was flushed out by He

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carrier gas at 25oC. The sample was heated from 25oC to 600oC at a heating rate of 5oC/min and

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the desorbed ammonia was measured using a thermal conductivity (TC) detector connected to

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the sample tube in a loop.

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3.2 in vitro catalysis experiments

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N-(3-Oxooctanoyl)-DL-homoserine lactone was used as a model compound in this study for in

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vitro testing of clay performance. Typically, a fixed amount of aqueous lactone solution (200

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ppm) was taken in a small vial containing a fixed amount (1mg – 500 mg) of clay or solid. The

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formed suspension was then agitated at 100 rpm for 15 minutes, and successively centrifuged (a

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Thermo Scientific Sorvall Legend T+ unit) at 3,500 rpm for 30 minutes. The supernatant was

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analyzed using an Agilent 1260 Infinity HPLC equipped with diode array detection (DAD) and

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Agilent Zorbax RX-C8 column (150mm x 4.6mm x 5µm). The identity of the products was

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confirmed on an Agilent LC/MS coupled to a Bruker AmaZon X ESI-ion trap mass

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spectrometer.

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3.3 Catalytic activity in biological system/disruption of quorum sensing in bacteria

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Method 1

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Five µl of Vibrio harveyi (ATCC14126, a luminous strain) bacterial culture (prepared overnight)

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was inoculated with 5 ml of Luria-Bertani broth (LB) + (LB + 2% NaCl) broth and at different

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clay loadings (10 to 10,000 µg/mL) in the system. A non-luminescent Vibrio parahaemolyticus

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strain was included as an additional negative control. Bacterial culture was incubated at 30oC

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with agitation (200 rpm) for 10 h. During the culturing period, bacterial growth was monitored

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by both optical density measurements at 600 nm (BioPhotometer, Eppendorf) and by a viable

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bacterial cell count on agar plates. The luminescent emission was detected and quantified by a

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luminescence detector (MiniLumat, EG &G Berthold) every hour. Blank experiments were also

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conducted to check if LB and clay would interfere with the detection of bacterial luminescence.

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Luminescent bacteria were added to LB at different amounts of clay, and the mixtures were

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immediately subjected to luminescence detection, which indicated no variation in the detected

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luminescence upon the addition of clay to the bacterial medium, signifying no interference in

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luminescence measurement.

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Method 2

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Five µl of Vibrio harveyi (ATCC14126, a luminous strain) bacterial culture prepared overnight

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was inoculated with 5 ml of LB+ broth and incubated at 30oC for 4 h. The cultured bacteria were

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separated (pellet) by centrifugation at 4000g for 10 min. The supernatant was collected and

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filtered through a syringe filter with a 0.45 µm pore size (PALL). The purpose of this step was to

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harvest quorum sensing molecules in the supernatant. Five ml of the filtrate was then mixed with

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different amounts of Calibrin Z to reach a final concentration of 0.5, 1, 10 and 50 mg/ml of

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Calibrin Z in the system. These suspensions were then incubated at 30oC for 1 h with agitation

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(200 rpm). A blank filtrate containing no added clay was also included as a control in each

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experiment. After incubation, the clays were separated from the filtrate by centrifugation at 5000

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RPM, followed by filtration of the supernatant through a 0.45 µm syringe filter as described

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above. It is expected that different amounts of clay would impact the separation of quorum

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sensing molecules differently, thereby, delaying the bioluminescence from a culture containing

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the least number of quorum sensing molecules. A 4 µl aliquot of a new and growing Vibrio

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harveyi bacterial culture (not yet luminescing) was inoculated into 4 ml of above filtrates, and

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the mixture was incubated at 30oC. The luminescent emission and the bacterial growth were

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quantified by a luminescence detector (MiniLumat, EG &G Berthold) and the optical density at

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600 nm (BioPhotometer, Eppendorf), respectively, at various time of the inoculation intervals.

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4. Results and discussion

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The removal of N-(3-Oxooctanoyl)-DL-homoserine lactone was studied in aqueous

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solutions at different temperatures (5-25oC) and at varying concentrations of lactone and clay

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amount (changing the ratio of lactone and clay), Table 1 shows one such representative data

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collected in triplicates at clay/lactone ratio of 50 (mg/mg) at 25 oC and 30 min reaction time. The

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concentration of the lactone in the reaction system was monitored using HPLC and LC-MS

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instrumental techniques. The percentage removal (% R) term in Table 1 indicates the extent of

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lactone removal from the aqueous solution. It was observed that clay catalysts degraded the

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lactone molecule to smaller fragments on the surface acid sites on the catalyst. The structure and

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mineralogy of Calibrin clays was described previously [11-12]. Other clays used here were

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commercial samples and their structures and mineralogy were confirmed by standard

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characterization methods. In the case of precipitated silica and kaolinite, the small amount of

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lactone removal happened totally through the adsorption process only as these materials did not

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have the required active sites/surface area for the degradation of lactone, the % lactone removal

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was 100% due to adsorption. Seemingly, the Lewis and Bronsted acid sites on the catalyst

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surface were active in degrading the lactone ring in the N-(3-Oxooctanoyl)-DL-homoserine

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lactone. As an example, Table 2 shows the structures and molecular weights of the lactone

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degradation products on Calibrin Z. Although the data shown in Table 1 was collected at 25oC,

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Calibrin clays were substantially active even at low temperature (up to 5 oC). Furthermore, there

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existed an optimum level (amount of the solid material) to function as a catalyst, and below that

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level the material just operated as an adsorbent. The two Calibrin products started to function as

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catalysts at a catalyst/lactone ratio of 15 (mg/mg) and above. In fact, Calibrin Z showed near

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100% catalytic degradation of lactone at a catalyst/lactone ratio of ~500.

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From the percentage lactone removal shown in Table 1 the strong activity of Calibrin

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clays for degrading the quorum sensing lactone is very clear. Generally, the surface area,

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porosity and the surface acid sites of the clay catalyst have a stronger influence on its

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performance in a catalytic reaction. The basic catalyst characterization data shown in Table 1

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correlated very well with their performance in the lactone removal and degradation under the

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given experimental conditions. The catalytic cleavage of N-(3-Oxooctanoyl)-DL-homoserine

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lactone molecule is mostly promoted by the acid sites, the number of such sites and their

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distribution in the solid material are crucial parameters to decide the progress of the reaction.

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Both the Calibrin clays have higher acidity, pore volume and surface area leading to their higher

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performance as catalysts/adsorbents in lactone removal. Silica, illite and kaolinite materials fared

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poorly in lactone removal which was probably due to their lower surface area, pore volume and

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weaker acidity. The N-(3-Oxooctanoyl)-DL-homoserine lactone used here is an organic

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molecule with an amide group linked to a saturated C8 fatty acid containing an oxo group at C3

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position (entry 6, Table 2). The molecule underwent catalytic cleavages at several positions in

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the molecule during the degradation as evidenced from the nature of the products (Table 2)

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formed and identified using LC-MS procedure described by Nievas et al. [14]. Some

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polymerized products of the original AHL molecules were also observed in LC-MS of the

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reaction mixture.

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At the next stage, we evaluated the performance of Calibrin Z clay in disrupting

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quorum sensing in a live/growing Vibrio harveyi bacteria. It is reported that the marine

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bacterium Vibrio harveyi ATCC BAA-1116, for example, channels the information of three AI

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signals into one QS cascade. Three receptors perceive these AIs, the hybrid histidine kinases

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LuxN, Lux(P)Q and CqsS, to transduce the information to the histidine phosphotransfer (HPt)

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protein LuxU via phosphorelay, and finally to the response regulator LuxO [15]. Recently, many

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other bacteria have been shown to control cell density-dependent functions through the excretion

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of and response to acyl-homoserine lactone autoinducers and the quorum sensing activity of such

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bacteria can be directly evaluated by measuring bioluminescence in bacterial cultures [16, 17].

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Besides, Vibrio harveyi is also a common pathogen causing vibriosis—a major disease of

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shrimps, fish, and shellfish that results in serious productivity and economic losses for

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aquaculture industry [18, 19].

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We used two different methods (1 and 2) to directly monitor [20, 21] the amount of

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luminescence emitted by the bacteria as the measure of catalytic quorum quenching performance

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of Calibrin Z. As shown in Figure 1, in method 1, Calibrin Z, at and above the inclusion level of

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1 mg/mL in the bacterial broth, starts to reduce the overall luminescence produced by the

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bacteria in comparison to the control (system without any added clay). In fact, at the clay

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concentrations of 10 mg/ml, the bacterial luminescence was reduced by 55% (from the area

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under the curves), respectively, which indicated a significant catalytic quorum quenching or

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interference in the overall quorum sensing of Vibrio harveyi by Calibrin Z clay. There already

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exist reports linking the bacterial population and luminescence reduction because of quorum

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quenching using different approaches [20, 21]. Importantly, as seen from Figure 2, the bacterial

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count during the measurement period was not reduced upon clay addition, confirming

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accomplishment of catalytic quorum quenching by transformation/separation of quorum sensing

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molecules or interference of quorum sensing process, and not by killing (antibacterial) of the

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bacteria in the system. Of course, the quorum sensing in bacteria is regulated by several factors

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and the presence of N-acylhomoserine lactones play a major role in this bacterial

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communication; clays could also have impacted chemical transformation and disruption of the

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overall quorum sensing process in some way or the other. The elucidation of the exact role of

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clays in impacting bioluminescence produced because of quorum sensing in Vibrio harveyi needs

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to be further investigated to confirm clay’s role in chemical transformations but direct

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interference of clays in impacting quorum sensing activity of the bacteria is confirmed from this

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study as luminescence is reduced without the loss of bacterial population in the Vibrio harveyi

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system.

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In method 2, the just formed quorum sensing molecules or their precursors in the Vibrio harveyi

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bacterial culture were first separated out in the form of a supernatant by centrifugation. The

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collected supernatant containing quorum sensing molecules was treated with different amounts

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of Calibrin Z clay and the luminescence was monitored with time. As seen in Figure 3, those

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systems that originated from clay-treated filtrates showed reduction in luminescence after 1h of

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growth, after which the intensity began to catch up. By 3 h of culture period, the luminescence

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recovered to the original level of the medium control. The amount of the clay impacted

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significantly the luminescence produced by the bacteria. Higher the clay amount, lower was the

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relative luminescence after 1 and 2 hours of bacterial cultures. The results proved that Calibrin Z

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clay caused a delay in the emission of luminescence by selectively interfering with the quorum

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sensing system of Vibrio harveyi without causing any change in bacterial population (Figure 4).

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As mentioned above, the exact role of the clay in disintegrating or transforming the quorum

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sensing molecules needs to be further explored and currently is beyond the scope of this paper.

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To the best of our knowledge, the disruption of quorum sensing molecules by catalysis of

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quorum sensing molecule is not reported thus far. As clays are regulatory compliant and safe for

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inclusion in animal feed, our approach of using clays as antagonists or catalysts to quench

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quorum sensing and thus bacterial communication could be a very promising method for

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controlling bacterial diseases caused to toxin secretion or other bacterial secretion resulting from

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quorum sensing activity.

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In conclusion, clays can be used as antagonists in quorum quenching of N-(3-

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Oxooctanoyl)-DL-homoserine lactone, a quorum sensing molecule by means of catalytic

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degradation of the lactone. Quorum sensing disruption activity of clays was also demonstrated in

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Vibrio harveyi wherein delaying of the bioluminescence gene expression was observed in these

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Gram-negative bacteria. In

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breakdown

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physicochemical properties such as structure, surface area, porosity, acidity, etc.

of

in vitro study, the performance of the clays towards catalytic

N-(3-Oxooctanoyl)-DL-homoserine

lactone

was

correlated

with

their

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3. Williams, P., Quorum Sensing, Communication and Cross-Kingdom Signalling in the

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12. Li, Y.; Lin, Y.; Yang, Y.; Wan X.; Chi, F. Effects of Naturally Mycotoxin-Contaminated

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Poult. Res., 2012, 21, 806-815.

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14. Nievas, F.; Bogino, P.; Sorroche F.; Giordano, W., Detection, Characterization, and

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15. Lorenz, N.; Shin, J.; Jung K., Activity, Abundance, and Localization of Quorum Sensing

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Receptors in Vibrio harveyi Front Microbiol. 2017; 8, 634, 1-10.

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16. Bassler, B.; Greenberg, E.; Stevens, A.; Cross-species induction of luminescence in the

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quorum-sensing bacterium Vibrio harveyi, J. Bacteriol., 1997, 179,12, 4043–4045.

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17. Fuqua, W. C., S. C. Winans, and E. P. Greenberg. Quorum sensing in bacteria: the LuxR-

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List of Tables and Figures

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Table 1. Physicochemical characteristics of clays and % Removal (R) of N-(3-Oxooctanoyl)-

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DL-homoserine lactone at 25oC and 30 min reaction time (catalyst/lactone = 50).

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Table 2. LC-MS data showing structures of various N-(3-Oxooctanoyl)-DL-homoserine lactone

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degradation products obtained on Calibrin Z at 25oC and 30 min reaction time (clay/lactone =

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50).

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Figure 1. Bacterial luminescence from the culture treated at different concentrations of Calibrin

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Z in the Vibrio harveyi culture; medium control, Vibrio parahaemolyticus. This data was

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obtained through method 1.

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Figure 2. Bacterial count measured as concentration (CFU/ml) of viable bacterial cells at each

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time point from Vibrio harveyi culture at different concentrations of Calibrin Z; medium control,

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Vibrio parahaemolyticus. This data was obtained through method 1.

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Figure 3. Relative luminescent emission (%) Vibrio harveyi cultures treated with initial Vibrio

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harveyi culture filtrates that were treated with various amounts of Calibrin Z. This data was

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obtained through method 2. The relative luminesce is based of luminesce measure at zero

370

amount of clay.

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Figure 4. Growth of Vibrio harveyi after mixing the initial Vibrio harveyi culture filtrates

372

treated with different concentrations of Calibrin Z. This data was obtained through method 2.

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373 374 375 376 377 378 379 380 381 382 Material

BETa

Pore volume,

surface area

DFTb

2

(m /g)

TPDc-NH3 acidity

%R

(150-350oC), mmol/g

(cm3/g)

Calibrin-A

141

0.32

0.025

53

Calibrin-Z

110

0.26

0.024

60

Illite

70

0.06

0.022

36

Kaolinite

32

0.04

0

5

Precipitated

340

1.0

0

25

SiO2 383

a

Brunauer–Emmett–Teller; b Density Functional Theory; c Temperature Programmed Desorption

384 385

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Journal of Agricultural and Food Chemistry

386 387 388 389

Table 1

390 391 392 393

Entry

m/z (amu)

1

86

2

102

3

114

4

141

5

157

6*

264

Proposed Structure

394 395 396 397 398 399 400 401 402 403 404 405 406

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*Starting (reactant) QS molecule Table 2

409 410

411 412

Figure 1

413

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414 415

Figure 2

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416 417

Figure 3

418

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419 420 421 422

Figure 4

423 424 425 426 427 428 429 430

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431

432 433 434 435

Figure : TOC Graphic

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Journal of Agricultural and Food Chemistry

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