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Bioactive Constituents, Metabolites, and Functions
Functional Metabolome Analysis of Penicillium roqueforti by Means of DOLC-NMR Richard Hammerl, Oliver Frank, Tina Schmittnägel, Matthias Ehrmann, and Thomas Hofmann J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b00388 • Publication Date (Web): 05 Apr 2019 Downloaded from http://pubs.acs.org on April 5, 2019
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Journal of Agricultural and Food Chemistry
1
Functional Metabolome Analysis of Penicillium
2
roqueforti by Means of DOLC-NMR
3 4 5
Richard Hammerl1, Oliver Frank1, Tina Schmittnägel1, Matthias A. Ehrmann2,
6
Thomas Hofmann13*
7 8 9 1Chair
10
of Food Chemistry and Molecular Sensory Science, Technische Universität
München, Lise-Meitner-Str. 34, D-85354 Freising-Weihenstephan, Germany
11
2Chair
12
of Technical Microbiology, Technische Universität München,
Gregor-Mendel-Str.4, D-85354 Freising-Weihenstephan, Germany, and
13
3Leibniz-Institute
14
for Food Systems Biology at the Technical University of Munich,
Lise-Meitner-Str. 34, D-85354 Freising-Weihenstephan, Germany
15 16 17 18 19
*
20
PHONE
+49-8161-712902
21
FAX
+49-8161-712949
22
E-MAIL
To whom correspondence should be addressed
[email protected] 23 24 25
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ABSTRACT
27 28
UPLC-TOF-MS profiling, followed by the recently reported DOLC-NMR and
29
quantitative 1H-NMR spectroscopy led to the differential qualitative analysis and
30
accurate quantitation of L-tryptophan-induced metabolome alterations of Penicillium
31
roqueforti, which is typically used in blue-mould cheese making. Among the 24
32
metabolites identified, two tetrapeptides, namely
33
D-Phe-L-Val-D-Val-L-Phe,
34
first time as metabolites of P. roqueforti. Antimicrobial activity tests showed strong
35
effects of the catabolic L-tryptophan metabolites 3-hydroxyanthranilic acid, anthranilic
36
acid, and 3-indolacetic acid against S. cerevisiae with IC50 values between 15.6 and
37
24.0 µg/mL, while roquefortine C and cis-bis-(methylthio)-silvatin inhibited the growth
38
of Gram negative Escherichia coli and Gram positive Bacillus subtilis with IC50 values
39
between 30.0 and 62.5 µg/mL.
D-Phe-L-Val-D-Val-L-Tyr
and
as well as cis-bis-(methylthio)-silvatin are reported for the
40 41
Keywords: Penicillium roqueforti, P. roqueforti, DOLC-NMR, differential off-line
42
LC-NMR, qHNMR, ERETIC 2, NMR bucket table
43
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Journal of Agricultural and Food Chemistry
INTRODUCTION
46 47
The ascomycete P. roqueforti, an aerobe fungus related to the family of
48
Trichocomaceae, is widely used for industrial applications, e.g. the production of
49
enzymes, as well as for the manufacturing of blue mould cheeses, where it
50
contributes to the unique flavor profile of the cheese by the biogeneration of odor-
51
active methyl ketones like 2-pentanone and 2-hexanone,1–3 as well as kokumi
52
enhancing γ-glutamyl dipeptides like γ-Glu-Glu and γ-Glu-Met, respectively.4
53
Studies on the optimal fermentation temperature show the highest metabolic
54
rates for P. roqueforti between 21 and 24 °C and microbial growth of the fungi can be
55
observed up to 32 °C.5,6 Penicillium species have been reported to metabolize amino
56
acids mainly via transamination to give the corresponding α-keto acids, some of which
57
are used for energy supply or a carbon source for more complex secondary
58
metabolites, or via a lyase-catalyzed elimination reaction that, for example, may lead
59
to the release of phenol from the progenitor amino acid L-tyrosine.7,8 In addition,
60
amino acids used as a carbon source when P. roqueforti is incubated in the presence
61
of carbohydrates like
62
fermentations seems to slow-down the general metabolism, e.g. the metabolic
63
generation of odor-active methyl ketones from triacylglycerides has been shown to
64
be significantly favoured when P. roqueforti is fermented in the presence of D-glucose
65
and amino acids when compared to fermentation with D-glucose alone.9,11
D-glucose.9,10
Lacking amino acids in P. roqueforti
66
The spectrum of secondary metabolites generated by P. roqueforti comprises
67
various classes, such as, e.g. alkaloids like roquefortines A-E, marcfortine A-C,
68
agroclacvine,
69
sesquiterpenes like eremofortin A-E, Penicillium roqueforti toxins (PR-toxins), (+)-
isofumigaclavine A
and
B
and
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festuclavine,
respectively,
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70
aristolochene, and valencene, and tetracyclic triterpenes like the andrastins A-D next
71
to a range of smaller metabolites like mycophenolic acid, bortyodiplodin and penicillic
72
acid.12–16 Some secondary molecules are used for chemical communication between
73
the cells of the fungus and, at the same time, inhibit microbial growth and affect
74
viability of competing microorganisms and pathogens.12,17 Other metabolites like
75
andrastin A
76
farnesyl-transferase in the RAS protein playing a key role in the control of cell
77
proliferation.12,18–20 Roquefortine C has been demonstrated to have a neurotoxic
78
effect in mice,21 is able to inhibit the growth of Gram-positive bacteria,22 and shows
79
an inhibition of the Cytochrom P450.23 In addition isofumigaclavine A, another
80
representative of a tryptophan derived secondary metabolite16, also showed lethal
81
effects in mice (LD50: 340 mg/kg) due to neurotoxic effects.24 Also mycophenolic acid
82
is well known to show antibacterial activity, but also to exhibit immunosuppressive
83
properties to animals.25,26
84
The biosynthesis of various metabolites like eremofortine A-C or Andrastin A-D starts
85
with acetyl-CoA which is transferred into farnesyl diphosphate (FPP) followed by
86
several enzymatic steps forming the target compound from aristolochene as
87
important intermediat.12,15 All known diketopiperazine derivatives are formed in the
88
beginning via the condensation of two amino acids, like L-tryptophan and L-histidine,
89
providing the cyclic metabolite.27
are
reported
to
exhibit
anticancer
activity
by
inhibiting
the
90
While various studies focused on the toxic secondary metabolites and
91
mycotoxin production of various Penicillium species,28,29 studies on Penicillium (P.)
92
roqueforti, used for the manufacturing of blue mould cheese, have been focused
93
primarily on the formation of secondary metabolites in cheese18 and silage13 or on the
94
volatile metabolome.12,30
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To investigate the impact of individual amino acids on the generation of
96
secondary metabolites from P. roqueforti, the aim of the present study was to apply
97
the Differential Off-Line LC-NMR approach (DOLC-NMR), a recently developed off-
98
line coupling of HPLC separation and 1H-NMR spectroscopy supported by automated
99
comparative bucket analyses and quantitative
1H-NMR
to record metabolome
100
changes in Saccharomyces cerevisiae upon nutrient interventions, to capture and
101
quantify amino acid induced metabolome alterations in P. roqueforti. NMR
102
spectroscopy, the method of choice, offers the possibility to detect new and unknown
103
metabolites independent of their ionization behaviour. In combination with a very
104
quick direct metabolite quantitation without using many structural complex internal
105
standards, this method constitutes a very strong tool for metabolome analysis.
106 107
MATERIALS AND METHODS
108 109
Chemicals. The following chemicals were obtained commercially: D-glucose,
110
deuterium oxide, methanol-d4, sodium azide, anthranilic acid, 3-hydroxyanthranilic
111
acid, 3-indolacetic acid, N-formylanthranilic acid were obtained from Sigma-Aldrich
112
(Steinheim, Germany), amino acids, malt extract, potassium hydroxide, potassium
113
dihydrogen phosphate, formic acid, methanol, 2-propanol, acetonitrile were from
114
Merck (Darmstadt, Germany). Water used for fermentation and chromatographic
115
separations was purified with a Milli-Q Integral 5 system (Millipore S.A.S., Molsheim,
116
France). TMSP-d4 was supplied by Euriso-Top (Gif-sur-Yvette, France). Synthetic air
117
was from Westfalen (Westfalen AG, Münster, Germany). Tetrapeptides were
118
obtained from Peptides&Elefants (Henningsdorf, Germany).
119
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Penicillium Roqueforti Fermentation. P. roqueforti ATCC10110 (CBS
121
221.30), originally isolated from a blue cheese in USA31, was used in this study. P.
122
roqueforti was obtained in ampoules containing a pellet of the lyophilized fungus as
123
spores. For the cultivation of the active fungi cells, the ampoule was opened and the
124
suspended spores were transferred into a growth medium containing malt extract
125
(4 g) and D-glucose (2 g) in water (100 mL) adjusted to pH 5.5 with 0.1% aqueous
126
NaOH. The mixture was moved on a shaking plate (100 rpm) in a glass flask (1 L)
127
sealed with an air permeable cap for 24 h at room temperature.
128
Fermentation of Penicillium Roqueforti in the Presence of Individual Amino
129
Acids. Aliquots (5 mL) of the solution with germinated spores were spiked with
130
individual proteinogenic
131
(100 mL) and D-glucose (0.15 g, 0.83 mmol), were moved in the flasks (1 L) sealed
132
with an air permeable cap on a shaking plate (100 rpm) for 96 h at 23 °C. In addition,
133
a control experiment was performed without any amino acid. Aliquots (5 µL) of the 21
134
samples were used for UPLC-ESI-TOF/MS screening, performed in five replicates for
135
each sample.
136
L-amino
Fermentation with/without
acids (5 mmol/L) and, after addition of water
L-Tryptophan
(Trp1/Trp0). A solution with the
137
geminated spores and the mycelium of P. roqueforti (as detailed above) was placed
138
in the fermenter (Biostat A Plus fermenter, Sartorius, Göttingen, Germany),
139
containing a solution of L-tryptophan (2 g; 5 mmol/L) and D-glucose (3 g, 16.7 mmol)
140
in 2 L water (Trp1 experiment). In addition, control experiments (Trp0) were performed
141
under the identical conditions without the presence of L-tryptophan. The fermentation
142
was performed under aerobic conditions (synthetic air, 1.3 L/min) whilst stirring
143
(150 rpm) for 96 h at 23 °C. The supernatants were then separated from fungi cells
144
by filtration (0.45 µm, Sartorius Stedium Biotech GmbH; Göttingen, Germany),
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Journal of Agricultural and Food Chemistry
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freeze-dried, and the residue obtained was taken up in water (15 mL). To capture the
146
differences in the metabolomes of fermentation batches Trp1 and Trp0, the obtained
147
extracts were used for RP18-MPLC separation to collect a total of 39 fractions each
148
in 1 min intervals, which were concentrated in vacuum by means of a HT-12
149
evaporation system (Genevac Limited Ipswich, United Kingdom), the corresponding
150
fractions collected from Trp1 and Trp0 were dissolved in deuterated solvents and then
151
analyzed by means of DOLC-NMR as detailed recently.32
152
Medium Pressure Liquid Chromatography (MPLC). The separation of the
153
fermentation broths (Trp0, Trp1) were performed on a Spot Prep II System (Gilson,
154
Limburg, Germany) equipped with a preparative 250 × 21.2 mm, 5 µm Luna
155
PhenylHexyl column (Phenomenex, Aschaffenburg, Germany) as the stationary
156
phase. The effluent (21.0 mL/min) was monitored at 230 nm. The gradient separation
157
was performed with aqueous formic acid (solvent A, 0.1% formic acid in water,
158
pH = 2.5) and acetonitrile (solvent B) as follows: After isocratic elution for 6 min at
159
2% B, the content of acetonitrile was increased to 15% B within 8 min, then an
160
isocratic step with 15% B for 6 min was performed, then B was increased to 30% B
161
within 12 min and, finally, to 100% B within 5 min, then isocratic for 4 min at 100% B.
162
In total 39 fractions (F3-F41) of 1 min intervals were collected and analyzed by means
163
of DOLC-NMR and LC-MS.
164
(2), and cis-bis-(methylthio)-silvatin (3), isolated from fractions F34, F38, and F41,
165
respectively, were identified for the first time as fermentation products of P. roqueforti.
166
D-Phe-L-Val-D-Val-L-Tyr,
D-Phe-L-Val-D-Val-L-Tyr
(1),
D-Phe-L-Val-D-Val-L-Phe
1, Figure 3: LC-MS (ESI+), m/z = 527.29 [M + H]+;
167
LC-MS/MS (DP = 10 V); UPLC-TOF/MSe, m/z = 120 (100), 219 (59), 247 (20), 182
168
(12), 281 (8), 340 (3); UPLC-TOF/MS, m/z = 527.2866 (measured), m/z = 527.2870
169
(calculated for [C28H39N4O6]+); 1H-NMR (500.13 MHz, MeOD-d4, COSY): δ = 7.36 [m,
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170
2H, H-C(6,8)], 7.30 [m, 2H, H-C(5,9)], 7.29 [m, 1H, H-C(7)], 6.99 [d, J = 8.5, 2H, H-
171
C(5´´´,9´´´)], 6.67 [d, J = 8.5, 2H, H-C(6´´´,8´´´)], 4.32 [dd, J = 4.8, 6.7, 1H, H-C(2´´´)],
172
4.23 [d, J =6.3, 1H, H-C(2´´)], 4.08 [d, J =9.3, 1H, H-C(2´)], 3.74 [dd, J =7.6, 1H, H-
173
C(2)], 3.11 [dd, J = 7.5, 13.5, 1H, H-C(3α)], 3.10 [dd, J = 6.8, 13.9, 1H, H-C(3´´´α)],
174
3.01 [dd, J = 7.5, 13.5, 1H, H-C(3β)], 2.84 [dd, J = 4.7, 13.9, 1H, H-C(3´´´β)], 2.22 [m,
175
1H, H-C(3´´)], 1.90 [m, 1H, H-C(3´)], 0.86 [d, J = 6.7, 3H, H-C(4´)], 0.85 [d, J = 6.7,
176
6H, H-C(4´´,5´´)], 0.65 [d, J = 6.7, 3H, H-C(5´)];
177
HSQC, HMBC): δ = 177.6 [C-1´´´], 173.4 [C-1´], 171.9 [C-1´´], 169.7 [C-1], 156.8 [C-
178
7´´´], 135.9 [C-4], 131.8 [C-5´´´,9´´´], 130.6 [C-5,9], 130.1 [C-6,8], 129.5 [C-4´´´], 128.8
179
[C-7], 116.0 [C-6´´´,8´´´], 60.7 [C-2´], 59.7 [C-2´´], 57.3 [C-2´´´], 55.7 [C-2], 38.8 [C-3],
180
37.9 [C-3´´´], 30.6 [C-3´], 29.8 [C-3´´], 20.0 [C-4´], 19.6 [C-4´´], 18.9 [C-5´], 17.9 [C-
181
5´´].
182
D-Phe-L-Val-D-Val-L-Phe,
13C-NMR
(125 MHz, MeOD-d4,
2, Figure 3: LC-MS (ESI+), m/z = 511.30 [M + H]+;
183
LC-MS/MS (DP = 10 V); UPLC-TOF/MSe, m/z = 120 (100), 219 (40), 247 (11), 166
184
(6), 265 (6), 386 (3), 346 (2), 340 (1); UPLC-TOF/MS, m/z = 511.2918 (measured),
185
m/z = 511.2920 (calculated for [C28H39N4O5]+); 1H-NMR (500.13 MHz, MeOD-d4,
186
COSY): δ = 7.36 [m, 2H, H-C(6,8)], 7.30 [m, 1H, H-C(7)], 7.28 [m, 2H, H-C(5,9)], 7.22
187
[m, 2H, H-C(6´´´,8´´´)], 7.18 [m, 1H, H-C(7´´´)], 7.17 [m, 2H, H-C(5´´´,9´´´)], 4.42 [dd,
188
J = 4.8, 7.2, 1H, H-C(2´´´)], 4.20 [d, J =6.5, 1H, H-C(2´´)], 4.07 [d, J =9.4, 1H, H-C(2´)],
189
3.75 [dd, J =7.6, 1H, H-C(2)], 3.21 [dd, J = 4.8, 13.8, 1H, H-C(3´´´α)], 3.10 [dd, J =
190
7.6, 13.6, 1H, H-C(3α)], , 3.00 [dd, J = 7.6, 13.6, 1H, H-C(3β)], 2.90 [dd, J = 7.2, 13.8,
191
1H, H-C(3´´´β)], 2.19 [m, 1H, H-C(3´´)], 1.90 [m, 1H, H-C(3´)], 0.84 [d, J = 6.7, 3H, H-
192
C(4´)], 0.83 [d, J = 6.7, 6H, H-C(4´´,5´´)], 0.69 [d, J = 6.7, 3H, H-C(5´)];
193
(125 MHz, MeOD-d4, HSQC, HMBC): δ = 177.3 [C-1´´´], 173.2 [C-1´], 171.6 [C-1´´],
194
169.8 [C-1], 139.3 [C-4´´´], 135.7 [C-4], 130.5 [C-5´´´,9´´´], 130.3 [C-5,9], 129.9 [C-
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13C-NMR
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Journal of Agricultural and Food Chemistry
195
6,8], 129.0 [C-6´´´,8´´´], 128.8 [C-7], 127.2 [C-4´´´], 60.6 [C-2´], 59.6 [C-2´´], 56.9 [C-
196
2´´´], 55.6 [C-2], 37.5 [C-3´´´], 37.1 [C-3], 30.5 [C-3´], 29.6 [C-3´´], 19.9 [C-4´´], 19.6
197
[C-4´], 19.2 [C-5´], 17.7 [C-5´´].
198
Cis-bis-(methylthio)-silvatin, 3, Figure 3: LC-MS (ESI+), m/z = 431.15
199
[M + Na]+; LC-MS/MS (DP = 10 V); UPLC-TOF/MSe, m/z = 337 (100), 107 (58), 217
200
(40), 245 (15), 293 (4), 361 (3); UPLC-TOF/MS, m/z = 431.1453 (measured), m/z =
201
431.1439 (calculated for [C20H28N2O3S2Na]+);
202
COSY): δ = 6.99 [d, J = 8.7, 2H, H-C(9/13)], 6.80 [d, J = 8.7, 2H, H-C(10/12)], 5.42
203
[ddqq, J = 1.3, 6.5, 1H, H-C(15)], 4.48 [d, J = 6.5, 2H, H-C(14)], 4.46 [s, 1H, H-C(3)],
204
3.34 [d, J = 14.1, 1H, H-C(7α)], 3.22 [s, 3H, H-C(19)], 3.20 [d, J = 14.1, 1H, H-C(7β)],
205
3.00 [s, 3H, H-C(20)], 2.29 [s, 3H, H-C(20)], 2.14 [s, 3H, H-C(22)], 1.78 [s, 3H, H-
206
C(18)], 1.73 [s, 3H, H-C(17)];
207
166.9 [C-2], 166.3 [C-5], 160.1 [C-11], 138.8 [C-16], 131.8 [C-9/13], 127.4 [C-8], 121.3
208
[C-15], 115.9 [C-10/12], 76.7 [C-6], 66.4 [C-3], 66.3 [C-14], 42.9 [C-7], 33.9 [C-20],
209
30.9 [C-19], 25.9 [C-18], 18.2 [C-17], 16.4 [C-21], 13.6 [C-22].
210
13C-NMR
1H-NMR
(500.13 MHz, MeOD-d4,
(125 MHz, MeOD-d4, HSQC, HMBC): δ =
Ultra Performance Liquid Chromatography Electrospray Ionization-
211
Time-of-Flight
Mass
Spectrometry
(UPLC-ESI-TOF/MS).
212
supernatant (5 µL) obtained from the P. roqueforti fermentation broths containing
213
individual amino acids were analysed by UPLC-ESI-TOF/MS on a Waters Synapt
214
G2-S HDMS mass spectrometer (Waters, Manchester, United Kingdom) coupled to
215
an Acquity UPLC core system (Waters, Milford, MA, USA) equipped with a 2 x
216
150 mm, 1.7 μm, BEH C18 column (Waters, Manchester, United Kingdom).
217
Chromatography was performed with a flow rate of 0.4 mL/min at 50 °C using a
218
solvent gradient starting with 99% aqueous formic acid (0.1% in water, pH = 2.5;
219
solvent A) and 1% acetonitrile containing 0.1% formic acid (solvent B) and increasing
9 ACS Paragon Plus Environment
Aliquots
of
the
Journal of Agricultural and Food Chemistry
220
solvent B to 100% within 4.5 min. Scan time for the MSe method (centroid) was set
221
to 0.1 s. Analysis were performed with negative and positive ESI+ in high-resolution
222
mode using the ion source parameters given in parenthesis: capillary voltage
223
(−2.0 kV), sampling cone (50 V), source off set (30 V), source temperature (120 °C),
224
desolvation temperature (450 °C), cone gas flow (2 L/h), nebulizer gas (6.5 bar),
225
desolvation gas (800 L/h). Data processing was performed by using MassLynx 4.1
226
SCN 9.16 (Waters, Manchester, United Kingdom) and the elemental composition tool
227
for determining the accurate mass. All data were lock mass corrected on the
228
pentapeptide leucine enkephaline (m/z = 554.2615, [M – H]-; m/z = 556.2771,
229
[M + H]+) in a solution (1 ng/μL) of acetonitrile/0.1% formic acid in water (1/1, v/v).
230
Scan time for the lock mass was set to 0.3 s, at intervals of 15 and 3 scans to average
231
with a mass window of ± 0.3 Da. Calibration of the Synapt G2-S in the range from
232
m/z 50 to 1200 was performed using a solution of sodium format (5 mmol/L) in
233
2-propanol/water (9:1, v/v). The collision energy ramp for MSe was set from 20 to
234
40 eV. The raw data of all fungi samples and replicates obtained from
235
UPLC-ESI-TOF/MS analysis were processed with Progenesis QI using the following
236
workflow: data import, review alignment, experiment design setup, peak picking (all
237
runs, limits automatic, sensitivity 3), review deconvolution, review compounds,
238
compound statistics and retention time limits 0.5-4.75 min. Compounds used for
239
principal component analysis (PCA) were filtered by means of ANOVA p value ≤ 0.05
240
and a fold change of ≥ 2. The processed data were exported to EZinfo, where the
241
matrix was analysed by PCA with pareto scaling.33,34 The same UPLC-TOF/MS
242
system with an identical solvent gradient was used for the determination of the exact
243
masses from the metabolites in the collected fractions.
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244
Nuclear Magnetic Resonance (NMR) Spectroscopy. 1D- and 2D-NMR
245
(COSY, HSQC, HMBC) experiments of the supernatant fractions of the fermentation
246
broth and purified compounds, respectively, were recorded at 300 K on a Bruker
247
AVANCE III 500 MHz System equipped with a cryo-TCI Probe and Topspin 3.2
248
software.35
249
DOLC-NMR Analysis. After concentration of each MPLC fraction in vacuum by
250
means of a HT-12 evaporation system (Genevac Limited, Ipswich, UK), the residues
251
obtained from fractions F3 - F23 were dissolved in D2O (1 mL) and aliquots (540 µL)
252
were, then, prior to NMR analysis, mixed with an aliquot (60 µL) of NMR-buffer, which
253
was prepared by dissolving KH2PO4 (10.2 g) in D2O (40 mL), adding KOH (1.5 g),
254
TMSP-d4 (50 mg), and NaN3 (5 mg), followed by pH-adjustment 7.0 with a solution of
255
KOH (4 mol/L) in D2O and making up to 50 mL with D2O. The more hydrophobic
256
fractions F24 - F41 were dissolved in MeOD-d4 (1 mL) and aliquots (600 µL) used for
257
NMR analysis. The individual fractions were analysed in 5 mm x 7’’ NMR tubes
258
(Z107374 USC tubes, Bruker, Faellanden, Switzerland). A 1H-NMR spectrum was
259
acquired using the Bruker standard water suppression pulse sequence (1D
260
noesygppr1d).36 The 90° pulse length (P1), power level for presaturation of the water
261
resonance (PL9) and O1 were adjusted individually on each sample and 16 scans
262
(NS) with 4 dummy scans (DS) were collected into 64 K data points using a spectral
263
width of 10273.97 Hz. The relaxation time (T1) was set to 20 s to allow all excited
264
nuclei to re-establish their equilibrium z-magnetization prior to the application of the
265
next pulse.35 To ensure high-quality spectra, the NMR probe was manually tuned and
266
matched (atmm) to 50 Ω resistive impedance to minimize radio frequency (RF)
267
reflection, with the sample in place. After automatic optimization of the lock phase,
268
each sample was shimmed (z1 − z5, xyz, z1 − z5), the 90° pulse width was determined
11 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
269
individually for each sample using the AU program pulsecal sn. All spectra were
270
acquired without spinning the sample and referenced to TMSP-d4 (0.0 ppm, fraction
271
F3-F23) or MeOD-d4 (3.31 ppm; fraction F24-F41). The free induction decay (FID)
272
was multiplied with a 0.3 Hz exponential line-broadening factor and zero-filled prior
273
to Fourier transformation. In case that the result of the automatic phase correction
274
with apk0.noe was not satisfying, a careful manual zero- and first-order phase
275
correction was performed. Baseline correction was done automatically with the
276
command absn. Integration was carried out manually and whenever required;
277
adjustment of the integrals was executed by the software functions SLOPE and
278
BIAS.35
279
NMR Bucketing. Corresponding to literature,37,38 NMR-buckets were calculated
280
using the Amix Viewer V3.9.13 Software (Bruker, Rheinstetten, Germany). Each
281
spectrum was referenced to TMSP-d4 (0.0 ppm; fraction F3-F23) or MeOD-d4
282
(3.31 ppm; fraction F24-F41). After checking the baseline offset and application of the
283
underground removal tool, the spectra were used to determine the buckets. Covering
284
the chemical shift region from -1 to 11 ppm, the width of each bucket was set to
285
0.1 ppm and the area between 4.5 and 5 ppm was excluded from bucketing (water
286
signal). The calculation of the absolute integral value for each of the 115 buckets was
287
performed successfully when the signal to noise ratio was higher than 10. The noise
288
was calculated in the region from 10 to 11 ppm, where no signals appeared. The
289
corresponding buckets from the fermenations Trp1 and Trp0, showing an integral ratio
290
(Trp1/Trp0) of >2 or 98% LC-MS) and analyzed by means of a
544
serial dilution microplate method39 to determine the minimum inhibitory concentration
545
(MIC) and the half-maximal inhibitory concentration (IC50) for each compound when
546
applied to Gram negative E. coli, the Gram positive B. subtilis, and the yeast
547
S. cerevisiae as test organisms.
548
Roquefortine C showed a MIC value of 62.5 and a IC50 value of 31.5 µg/mL for
549
B. subtilis (ATCC 6633), respectively (Table 2), thus being well in line with data
550
reported in literature (0.1 mg/mL) for Gram positive B. subtilis (IMM 313).54 For E. coli
551
(ATCC 23226) a IC50 value of 62.5 µg/mL and a MIC value of 125 µg/mL could be
552
detected. Previously performed studies on E. coli regarding an inhibitory effect
553
caused by roquefortine C showed no effect against E. coli (ATCC 11775) at
554
100 µg/mL.22 Another undefined E.coli was not inhibited at 30 µg/disk.55 Comparing
555
the strains to each other, differences between the microorganisms can be observed
556
regarding the occurring enzymes which may explain the differences in the growth
557
rates in the presence of the inhibitor.
558
In comparison, cis-bis-(methylthio)-silvatin (3) showed a lower IC50 value of 30 µg/mL
559
for for E. coli and B. subtilis, respectively. Interestingly, the catabolic L-tryptophan
560
metabolites anthranilic acid (4), 3-indolacetic acid (5) and 3-hydroxyanthranilic acid
561
(6), which induced growth inhibition of the yeast S. cerevisiae with a MIC value of
562
62.5, 31.5 and 31.5 µg/mL, respectively, while N-formylanthranilic acid (11) showed
563
a significant higher MIC value at 250 µg/mL. These data confirm previous reports on
564
the inhibitory activity of 3-hydroxyanthranilic acid on the growth of S. aureus,
565
S. epidermidis, respectively.56 An inhibitory effect on the fungi C. albicans was not
23 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
Page 24 of 46
566
detectable56,57 but the inhibition of S. cerevisiae has been reported for the first time.
567
The mode of action is probably similar to preservatives due to structural similarity.
568
The weak acid enters the microorganism and after the dissociation step, the
569
metabolism is disturbed because of a intracellular reduced pH value.58
570
In this study the growth of E. coli (ATCC 23226) was not affected by
571
3-hydroxyanthranilic acid. Data from literature showed a inhibition of another strain of
572
E. coli (ATCC 11775) at 102.4 µg/mL.56 Due to different enzymatic systems between
573
the analysed strains, the differences may be explained.
574
Moreover, anthranilic acid is reported as effective preservative for animal fodder in
575
concentration of 0.3 to 0.4%59 and suppresses cell proliferation of mesangial cells by
576
32% at 10-6 M.60 The sesquiterpene eremofortin B (8) showed a MIC value of
577
125 µg/mL for the growth inhibition of S. cerevisiae, which has not yet been reported
578
in literature. Also andrastin A (10) showed inhibited the growth of S. cerevisiae (MIC
579
= 62.5 µg/mL), which may be explained by the inhibition of the protein
580
farnesyl-transferase as reported for eukaryotic cells.20 Comparatively, high IC50
581
values of 187
582
tetrapeptides
583
acids with D-conformation are formed via racemisation of L-amino acids. Peptides
584
containing the L-conformer are more stable against proteolytic degradation, which
585
leads to higher half-life periods in organisms.61 Many antibiotics like penicillin G or
586
food toxins like isocereulides derivatives own D-amino acids.62,63 In addition, small
587
peptides with aromatic residues of D-phenylalanine, D-tyrosine or D-tryptophan are
588
described to have a high binding possibility to proteins accompanied with an inhibition
589
of its functionality, respectively.64
and 250 µg/mL, respectively, were found for the identified
D-Phe-L-Val-D-Val-L-Tyr
(1) and
D-Phe-L-Val-D-Val-L-Phe
24 ACS Paragon Plus Environment
(2). Amino
Page 25 of 46
Journal of Agricultural and Food Chemistry
590
In conclusion, DOLC-NMR spectroscopy, followed by qHNMR using
591
ERETIC 2, has been successfully used to monitor metabolome alterations in
592
P. roqueforti induced upon an intervention with
593
metabolites identified, two tetrapeptides, namely
594
D-Phe-L-Val-D-Val-L-Phe
595
for the first time as metabolites of P. roqueforti. Antimicrobial activity tests showed
596
strong effects of the catabolic
597
3-indolacetic acid (5) and 3-hydroxyanthranilic acid (6) against S. cerevisiae with IC50
598
values between 15.6 and 24.0 µg/mL. In comparison, roquefortine C (7) and
599
cis-bis-(methylthio)-silvatin (3) inhibited the growth of Gram negative E. coli and
600
Gram positive B. subtilis with IC50 values between 30.0 and 62.5 µg/mL. Future
601
studies will focus on the one hand on the concentrations of these compounds in
602
P. roqueforti fermented dairy products like blue mould cheeses and on the other hand
603
on inhibitory effects of the identified compounds regarding pathogens and food
604
related microorganisms.
L-tryptophan.
Among the 24
D-Phe-L-Val-D-Val-L-Tyr
(1) and
(2), as well as cis-bis-(methylthio)-silvatin (3) are reported
L-tryptophan
metabolites anthranilic acid (4),
605 606 607
SUPPORTING INFORMATION AVAILABLE
608
Fermentation conditions and NMR data are available free of charge via the Internet
609
at http://pubs.acs.org.
610 611 612 613
25 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
614
Table 1.
Concentration of Key Metabolites in the P. roqueforti ferment in the absence (control, Trp0) and presence of L-tryptophan (Trp1).
615
conc. (μmol/L) in
metabolite
a
Trp1
Trp0
D-Phe-L-Val-D-Val-L-Tyr
(1)
n.d.a
2.4 (±0.2)
D-Phe-L-Val-D-Val-L-Phe
(2)
n.d.a
0.53 (±0.05)
cis-bis-(methylthio)-silvatin (3)
0.86 (±0.09)
n.d.a
anthranilic acid (4)
29.4(±3.0)
n.d.a
3-indolacetic acid (5)
4.1 (±0.4)
n.d.a
3-hydroxyanthranilic acid (6)
442.7 (±45.6)
n.d.a
roquefortine C (7)
1.6 (±0.2)
0.53 (±0.05)
eremofortin B (8)
n.d.a
1.7 (±0.2)
scytalone (9)
n.d.a
1.6 (±0.2)
andrastin A (10)
0.79 (±0.08)
0.92 (±0.09)
67.4 (±7.0)
n.d.a
trehalose
15.9 (±1.7)
14.4 (±1.5)
nicotinic acid
21.0 (±2.2)
n.d.a
uridine
6.5 (±0.7)
n.d.a
tyrosine
6.5 (±0.7)
1.8 (±0.2)
fumaric acid
3.5 (±0.4)
n.d.a
succinic acid
20.2 (±2.1)
6.4 (±0.7)
β-hydroxyisobutyric acid
3.9 (±0.4)
7.0 (±0.7)
kynurenine
7.9 (±0.8)
n.d.a
isopropylmalic acid
2.4 (±0.2)
n.d.a
catechol
58.1 (±6.0)
n.d.a
tyrosol
n.d.a
0.60 (±0.06)
kynurenic acid
43.1 (±4.4)
n.d.a
p-hydroxy-2-phenylacetic acid
2.4 (±0.2)
n.d.a
N-formylanthranilic
616
Page 26 of 46
acid (11)
not detectable
617
26 ACS Paragon Plus Environment
Page 27 of 46
618
Journal of Agricultural and Food Chemistry
Table 2.
Minimum Inhibitory Concentration (MIC) and Half-Maximal Inhibitory
619
Concentration (IC50) of P. roqueforti Metabolites Isolated from the
620
Fermentation broths Trp0 and Trp1 against different microorganisms. MIC and IC50 values (µg/mL) metabolite S. cerevisiae IC50
MIC a
D-Phe-L-Val-D-Val-L-Tyr
(1)
187
n.i.
D-Phe-L-Val-D-Val-L-Phe
(2)
250
n.i.
b
a b
B. subtilis IC50 a
n.i.
a
E. coli
MIC a
n.i.
a
n.i.
n.i. n.i.
b
IC50 a
n.i.
a
MIC a
n.i.
a
n.i.
n.i.
30
n.i.
250
n.i.
187
250
b
cis-bis-(methylthio)-silvatin (3)
n.i.
n.i.
30
anthranilic acid (4)
24
62.5
n.i.
n.i.
3-indolacetic acid (5)
15.6
31.5
250
n.i.
3-hydroxyanthranilic acid (6)
15.6
31.5
250
n.i.
n.i.
n.i.
roquefortine C (7)
250
n.i.
31.5
62.5
62.5
125
eremofortin B (8)
62.5
125
250
n.i.
250
n.i.
scytalone (9)
n.i.
n.i.
n.i.
n.i.
andrastin A (10)
47
62.5
200
n.i.
N-formylanthranilic
b
a
b
a
b
a
acid (11)
a a a
a b a
a
b
a
a
a b
n.i.
n.i.
250
n.i.
a
a a
621
225 250 n.i. n.i. 250 n.i. a No inhibition observable until a tested maximum concentration of 250 µg/mL; b No
622
inhibition observable until a tested maximum concentration of 60 µg/mL.
623
27 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
624
Page 28 of 46
Figure Captions
625 626
Figure 1. Principle component Analysis of UPLC-ESI-TOF/MS full scan data
627
(50−1200 Da, ESI−) of medium broths of P. roqueforti fermented for 96 h at 23 °C in
628
the absence and presence of individual proteinogenic L-amino acids (five replicates
629
per sample).
630 631
Figure 2. (A) RP-MPLC chromatograms of the P. roqueforti fermentation performed
632
in the presence (Trp1) and absence of L-tryptophan (Trp0); (B) Differential NMR
633
bucket analysis of fractions F3−F41 showing the integral ratio (Trp1/Trp0) and
634
chemical shift of metabolites affected by the L-tryptophan intervention.
635 636
Figure 3.
Chemical
structures
of
identified
secondary
metabolites
637
D-Phe-L-Val-D-Val-L-Tyr
638
(3), anthranilic acid (4), 3-indolacetic acid (5), 3-hydroxyanthranilic acid (6),
639
roquefortine C (7), eremofortin B (8), scytalone (9), andrastin A (10) and
640
N-formylanthranilic
(1), D-Phe-L-Val-D-Val-L-Phe (2), cis-bis-(methylthio)-silvatin
acid (11), respectively.
641 642
Figure 4. 1H-NMR (500.13 MHz, MeOD-d4, 300 K, zg30) excerpts (6.5 - 7.7 ppm, 3.5
643
- 4.5 ppm) of (A) D-Phe-L-Val-D-Val-L-Tyr (1) isolated from Trp0 fermentation fraction
644
F34,
645
D-Phe-L-Val-D-Val-L-Phe
646
the synthetic reference D-Phe-L-Val-D-Val-L-Phe; 1H-NMR signal assignment is done
647
according to Figure 3.
(B)
the
synthetic
reference
D-Phe-L-Val-D-Val-L-Tyr,
(C)
(2) isolated from the Trp0 fermentation fraction F38, and (D)
28 ACS Paragon Plus Environment
Page 29 of 46
Journal of Agricultural and Food Chemistry
648
Figure 5. Excerpt of the HMBC spectrum (500.13 MHz, 125 MHz, MeOD-d4, 300 K;
649
3.7-4.4 ppm, 125-180 ppm) of D-Phe-L-Val-D-Val-L-Tyr (1) showing the sequence of
650
the single amino acids in the tetrapeptide backbone.
651
with arrows.
2/3J
H-C-correlations
are marked
652 653
Figure 6. (A) MSe spectra (ESI+) of D-Phe-L-Val-D-Val-L-Phe (2) including the exact
654
mass, calculated elemental composition and chemical formula with a1/2/3, b1/2/3 and
655
y1/2/3 cleavage of the tetrapeptide; (B) MS2 spectra (ESI+) of peptide 6 showing the
656
cleavage fragments.
657 658
Figure 7. Excerpt of the HMBC spectrum (500.13 MHz, 125 MHz, MeOD-d4, 300 K;
659
2.8-7.2 ppm, 10-180 ppm) of cis-bis-(methylthio)-silvatin (3) showing the key
660
correlations of H-C(3), H-C(7) and H-C(14) marked with arrows.
2/3J
H-C
661 1H-NMR
662
Figure 8. Quantitative
spectroscopy (500.13 MHz, MeOD-d4, 300 K,
663
noesygppr1d) to determine the concentration of andrastin A (10) via the quantifier
664
signal at 5.24 ppm (H-(11), s, 1H) and cis-bis-(methylthio)-silvatin (3) via the quantifier
665
signal at 6.80 ppm (H-(10/12), d, 2H) in fraction F41.
666 667 668
29 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
669
Hammerl et al. (Figure 1)
670 671
672 673 674 675 676 677 678 679
30 ACS Paragon Plus Environment
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Page 31 of 46
680
Journal of Agricultural and Food Chemistry
Hammerl et al. (Figure 2)
681 682
683 684 685
31 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
686
Hammerl et al. (Figure 3)
687 688
689 690 691 692 693
32 ACS Paragon Plus Environment
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Page 33 of 46
694
Journal of Agricultural and Food Chemistry
Hammerl et al. (Figure 4)
695 696
697 698 699 700 701 702 703 704 705 706
33 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
707
Hammerl et al. (Figure 5)
708
709 710 711 712 713
34 ACS Paragon Plus Environment
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Page 35 of 46
714
Journal of Agricultural and Food Chemistry
Hammerl et al. (Figure 6)
715 716
717 718 719 720
35 ACS Paragon Plus Environment
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721
Hammerl et al. (Figure 7)
722
723 724 725
36 ACS Paragon Plus Environment
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Page 37 of 46
726
Journal of Agricultural and Food Chemistry
Hammerl et al. (Figure 8)
727
728 729 730 731 732 733 734 735 736 737 738
37 ACS Paragon Plus Environment
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739
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