Viewpoint pubs.acs.org/est
Halophyte-Endophyte Coupling: A Promising Bioremediation System for Oil-Contaminated Soil in Northwest China Shuai Zhao, Na Zhou, Lei Wang, and Chang-Yan Tian* State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China as 70−80 °C and the annual precipitation is just 105.6 mm, but with an annual evaporation of 3008.9 mm. The Ministry of Environmental Protection in China (MEP) has used the approach of the USEPA to deal with oil pollution by inoculating exogenous and indigenous oil-utilizing microorganisms in this area. However, their hydrocarbon-attenuation potential subjected to the environmental stress of Northwest China is limited because the alien species cannot be sustained to reach a viable population size. Phytoremediation using plant-microbe technology is a simple, cost-effective approach for cleaning oily soils, because plants can offer a stable habitat for maintaining viable populations of bacteria with remediation activities. In in vitro conditions, components of plant root exudates support growth of metabolically active bacteria in contaminated soils to degrade polycyclic aromatic hydrocarbon (PAHs).2 In in-vivo conditions, this unique plant niche provides the xenobiotic degrader strains with an ability to sustain population sizes due to reduced competition. For instance, Burkholderia cepacia L.S.2.4 is a natural endophyte of yellow lupine, the engineered strain that contains a toluene-degradation gene that strongly degrades toluene and helps reduce evapotranspiration by 50− ith the demand for crude oil as an energy source, oil 70% through the leaves.3 However, severe climate and extraction in Northwest China has been increasing hypersaline soils limit the use of these glycophytes and their dramatically from 1.94 million tons in 2000 to 7.35 million tons associated microbes in recovery efforts from oil contamination in 2012. As a result, the associated problem of oil pollution in in Northwest China. this area has reached acute dimensions. In situ bioremediation Halophytes are plants that can only grow in hypersaline using microbes has been proposed as one of the best solutions areas. Scientists have found halophytes not only host beneficial for dealing with oil contaminated soil. The United States microorganisms, such as plant growth-promoting endophytic Environmental Protection Agency (USEPA) successfully bacteria, but also harbor hydrocarbon-utilizing microflora. For introduced microbes into the oil contaminated bay area of instance, the rhizosphere of the halophyte Halonemum Alaska. However, microbial activity is sometimes constrained by strobilaceum, which occupies the coastal regions of the Arabian environmental factors such as regional climate, soil characterGulf, is equipped with extremely halophilic oil-utilizing istics, and vegetation, which are particularly problematic in microorganisms.4 We note that in oil contaminated hypersaline Northwest China. Plants can provide shelter for microbes areas of Northwest China, there exist some naturally occurring during severe environmental conditions, which also assist the halophilic plants, for example, Limonium Mill. (Plumbaginaceae). It is hoped that halophytes, as the carrier associated with microbes in reducing ambient environmental stress.1 In our appropriate rhizo- and endophytic bacteria, could overcome the opinion, planting halophytes and inoculating them with constraints of oily hypersaline drought environments. halophyte associated microbes may be a worthwhile practical Although halophyte-microbes are thought to be of potential approach for reclaiming oil contaminated hypersaline soils in benefit to the rehabilitation of oil-polluted hypersaline soils in the arid and semiarid areas of Northwest China. arid and semiarid regions of Northwest China, there are certain Oil fields in Northwest China are located within an arid and factors that cannot be underestimated due, in part, to the semiarid climatic zone, frequently in the desert, or Gobi. They complexity of the plants’ exterior and interior environments. are far from the sea and considered to be a saline basin in which evaporation exceeds fresh water influx, and contain little vegetation with great seasonal extremes in temperature. In Received: September 22, 2013 Karamay, the largest oil field in Northwest China, the monthly Revised: October 8, 2013 average temperature is −18.9 °C in January and soars to 33.9 Accepted: October 11, 2013 Published: October 24, 2013 °C in July, soil surface temperature sometimes reaches as high
W
© 2013 American Chemical Society
11938
dx.doi.org/10.1021/es404219j | Environ. Sci. Technol. 2013, 47, 11938−11939
Environmental Science & Technology
Viewpoint
Furthermore, there remains a lack of corresponding data to support this hypothesis. Since there is a singularity of species and a very low number of halophytes growing in oil-polluted hypersaline soils, further investigations are needed to examine the practicality of expanding their cultivation while growing other halophytes together with local plants. There is also a need to investigate how much water the halophytes require, while at the same time avoiding infiltration of oil pollutants. In addition, since the interior environment of halophytes differs from the exterior environment, further investigations are required to examine whether exogenous endophytes can grow and become conditioned pathogens. There are a number of investigations that can be carried out to examine these problems. First, one can screen for potentially suitable halophytes by using extensive assaying of halophytes growing on oil-contaminated soils. Northwest China contains more than 60% of the halophyte resources in China, which would provide an excellent center for such a screening procedure. With respect to water use in arid and semiarid regions, drip-irrigation has been found to be an efficient way of reducing water use and controlling irrigation volumes.5 Finally, endophytic pollutant degraders in native halophytes need to be screened, and potential halophyte−endophyte combinations tested under hypersaline oil-contaminated field conditions. Additionally, suitable non-native endophytes could be introduced into China. Only when such aspects are addressed can phytoremediation of hypersaline oil-contaminated soils using halophyte−endophyte association systems have a promising future in Northwest China.
■
AUTHOR INFORMATION
Corresponding Author
*Phone: +86-991-7885301; fax: +86-991-7885320; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■ ■
ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (31300432). REFERENCES
(1) Becerra-Castro, C.; Kidd, P. S.; Prieto-Fernandez, A.; Weyens, N.; Acea, M. J.; Vangronsveld, J. Endophytic and rhizoplane bacteria associated with Cytisus striatus growing on hexachlorocyclohexanecontaminated soil: Isolation and characterization. Plant Soil. 2011, 340 (1−2), 413−433. (2) Child, R.; Miller, C. D.; Liang, Y.; Narasimham, G.; Chatterton, J.; Harrison, P.; Sims, R. C.; Britt, D.; Anderson, A. J. Polycyclic aromatic hydrocarbon-degrading Mycobacterium isolates: Their association with plant roots. Appl. Microbiol. Biotechnol. 2007, 75 (3), 655−663. (3) Barac, T.; Taghavi, S.; Borremans, B.; Provoost, A.; Oeyen, L.; Colpaert, J. V.; Vangronsveld, J.; van der Lelie, D. Engineered endophytic bacteria improve phytoremediation of water-soluble, volatile, organic pollutants. Nat. Biotechnol. 2004, 22 (5), 583−588. (4) Al-Mailem, D. M.; Sorkhoh, N. A.; Marafie, M.; Al-Awadhi, H.; Eliyas, M.; Radwan, S. S. Oil phytoremediation potential of hypersaline coasts of the Arabian Gulf using rhizosphere technology. Bioresour. Technol. 2010, 101 (15), 5786−5792. (5) Wang, L.; Zhao, Z. Y.; Zhang, K.; Tian, C. Y. Reclamation and utilization of saline soils in arid northwestern China: A promising halophyte drip-irrigation system. Environ. Sci. Technol. 2013, 47 (11), 5518−5519. 11939
dx.doi.org/10.1021/es404219j | Environ. Sci. Technol. 2013, 47, 11938−11939
