Application of a novel bacterial consortium BDAM for bioremediation of bispyribac sodium in wheat vegetated soil
Graphical abstract
Introduction
Herbicides are phytotoxic chemicals belonging to various classes, used for destroying weeds or inhibiting their growth and increasing agricultural production. The use of herbicides has increased dramatically during the last two decades, corresponding to changes in farming practices. Usually, herbicides interfere with certain biochemical reactions, and hence may hamper seed germination, establishment of seedlings and development/growth of plants [1]. Once released into the environment, the fate of herbicides is dependent on their physicochemical properties like water solubility, vapor pressure, soil organic carbon coefficient (Koc) and octanol-water partition coefficient (Kow), and most importantly the biological transformation [[2], [3], [4]]. Most of the herbicides or their metabolites persist in the environment, remain active there and cause soil and water contamination.
Bispyribac-sodium (sodium 2,6-bis[(4,6-dimethoxypyrimidine-2-yl)oxy]benzoate) (BS) is a broad spectrum herbicide of the class pyrimidinyl benzoic acid. It is a post-emergence, systemic and selective herbicide which is absorbed by underground and aerial parts of the plants [5]. Like other pyrimidinyl benzoic acid herbicides, BS hinders the acetolactate synthase (ALS) pathway in plants and microbes which is responsible for the synthesis of branched-chain amino acids, e.g. leucine, isoleucine and valine [6,7].
Studies regarding weed control efficacy showed that BS is highly proficient against a number of weeds including Murdannia keisak [8,9] and is widely used for the effective control of weeds in the transplanted and direct seeded rice crops worldwide [10,11]. Runoff and leaching from agricultural soils, or accidental spills can cause contamination of water bodies with BS [12,13]. Toxicity of BS to different fresh water life forms has already been reported [14,15]. In addition, the presence of BS residues in agricultural soil can affect the establishment of subsequent crop [16,17]. Furthermore, just like many other herbicides [18], presence of BS and its metabolites in agricultural soil can inhibit abundance and metabolic activities of native microbes [19,20].
The problems related to the contamination of soil and water with BS residues, emphasize that remediation of this herbicide is imperative. Such, environmental issues also denote that herbicide need to be degraded in agricultural soils, i.e., at point source, before it enters the environment especially water bodies.
Exploitation of plant-microbial associations for the remediation of contaminated soil has been reported as cost-effective, restorative of soil texture and less invasive technique [[21], [22], [23]]. Our previous findings showed that inoculation of plants with selected bacterial strains enhanced their phytoremediation efficiency for pesticides [24,25]. Inoculated pollutant degrading bacteria help the host plants to acclimatize in the polluted environment by reducing the level of contamination through mineralization and increasing plant growth and development [26]. In such systems, plant root exudates enhance the activity and density of the inoculated pollutant-degrading bacteria within the rhizosphere and rhizosheath [27]. Also, plants can absorb toxic organic compounds from the polluted soil through their underground parts [25]. In the plant endosphere, these pollutants may have different fates, for example; some get metabolized by the plants or endophytic bacteria while others may translocate to various plant parts through xylem and phloem [28]. Although the success of plant-bacterial associations in the mitigation of a number of toxic organic contaminants including pesticides has been reported [[29], [30], [31]]. To the best of authors knowledge, no report has yet been published regarding remediation of bispyribac sodium (BS) using plant-bacteria partnerships.
In this work, we used previously isolated highly efficient BS degrading bacterial consortium BDAM [32] to investigate its bioremediation potential in wheat (Triticum aestivum) vegetated soil. Effect of the consortium BDAM on plant growth parameters, and the potential of plant-bacterial partnership for remediation of BS in rhizo- and endosphere of the wheat plant was investigated.
Section snippets
Chemicals, enzymes and growth media
Technical grade (96%) and analytical standard (99%) bispyribac sodium used in this study were obtained from Four Brother Group, Pakistan and Sigma-Aldrich respectively. Dichloromethane (DCM), n-hexane, methanol, acetone and HPLC grade acetonitrile were purchased from Merck Pvt Ltd/Sigma-Aldrich. Restriction enzymes (Hind-III) and primers were purchased from Fermentas. Tryptone, yeast extract, and sodium chloride with their respective concentrations of 10 g L−1, 5 g L−1, and 5 g L−1, used to
Biomass of the plant
Efficiency of the bacterial consortium BDAM for growth and development of wheat plants (W1) vegetated in BS contaminated and native soil was studied. Plant growth parameters including seed germination (SG), root length (RL), shoot length (SL), root dry weight (RDW) and shoot dry weight (SDW) are presented in (Table 1, Table 2). Results showed that in the spiked soil (P-UI), the rate of seed germination was significantly (P < 0.05) less, i.e., 20% and 22% as compared to the control (C1) i.e.,
Discussion
Plant-bacterial association seems to be an effective, inexpensive and environment-friendly approach for the degradation of hazardous xenobiotics including insecticides and herbicides [34,35]. Many reports are available showing manipulation and exploitation of beneficial plant-microbe interactions to increase the plant growth and crop yields sustainably [36,37]. Harnessing plant microbe interactions for other applications e.g. bioremediation of organic pollutants including insecticides and
Conclusion
Bacterial consortium BDAM and wheat rhizosphere proved to be an 'ecological remediation unit' to treat BS contaminated soils by virtue of plant-bacterial partnerships as indicated by complete removal of the added BS from soil. Successful colonization and survival of bacterial strains namely Achromobacter xylosoxidans BD1 and Achromobacter pulmonis BA2 was observed in the rhizosphere, while Ochrobactrum intermedium BM2 colonized both in rhizo- as well as plant endosphere.
Decreased BS
Conflict of interests
The authors declare that they have no conflict of interest.
Acknowledgment
Authors greatly acknowledge Dr. Sajjad Mirza NIBGE for granting access to the HPLC.
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