Microbial degradation has been considered as a rapid, green, and cost-effective technique to reduce insecticide pollutions in a contaminated environment. However, the instability and low efficacy of non-indigenous microorganisms hampers their further exploitation when being introduced into a real environmental matrix. In order to overcome the restriction that these functional microorganisms are under, we investigated the optimal conditions to improve the pyrethroid-degrading ability of one previously isolated bacterium Bacillus cereus BCC01, where 9.6% of the culture suspension (with cell density adjusted to OD600 = 0.6) was inoculated into 50 mL media and cultivated at pH 8 and 30 °C, and its metabolic pathway was illuminated by analyzing the main metabolites via gas chromatography mass spectrometry (GC-MS). Most importantly, a key pyrethroid-hydrolyzing carboxylesterase gene estA was identified from the genomic library of strain BCC01, and then expressed in Escherichia coli BL21 (DE3). After purification, the recombinant protein EstA remained soluble, displaying high degrading activity against different pyrethroids and favorable stability over a wide range of temperatures (from 15 °C to 50 °C) and pH values (6.5–9). Therefore, the EstA-associated biodegradation of pyrethroids was determined, which could provide novel insights to facilitate the practical application of B. cereus BCC01 in the microbial detoxification of pyrethroid contamination.

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The well-studied quorum sensing (QS) mechanism has established a complex knowledge system of how microorganisms behave collectively in natural ecosystems, which contributes to bridging the gap between the ecological functions of microbial communities and the molecular mechanisms of cell-to-cell communication. In particular, the ability of agrochemical degradation has been one most attractive potential of functional bacteria, but the interaction and mutual effects of intracellular degradation and intraspecific behavior remained unclear. In this study, we establish a connection between QS regulation and biodegradation by harnessing the previously isolated Bacillus subtilis BSF01 as a template which degrades various pyrethroids. First, we characterize the genetic and transcriptional basis of comA-involved QS system in B. subtilis BSF01 since the ComQXPA circuit coordinates group behaviors in B. subtilis isolates. Second, the genetic and transcriptional details of pyrethroid-degrading carboxylesterase CesB are defined, and its catalytic capacity is evaluated under different conditions. More importantly, we adopt DNA pull-down and yeast one-hybrid techniques to reveal that the enzymatic degradation of pyrethroids is initiated through QS signal regulator ComA binding to carboxylesterase gene cesB, highlighting the synergistic effect of QS regulation and pyrethroid degradation in B. subtilis BSF01. Taken together, the elucidated mechanism provides novel details on the intercellular response of functional bacteria against xenobiotic exposure, which opens up possibilities to facilitate the in-situ contaminant bioremediation via combining the QS-mediated strategies.

Background Massive techniques have been evaluated for developing different pest control methods to minimize fertilizer and pesticide inputs. As “push-pull” strategy utilizes generally non-toxic chemicals to manipulate behaviors of insects, such strategy is considered to be environmentally friendly. “Push-pull” strategy has been extraordinarily effective in controlling stem borers, and the identification of new “pushing” or “pull” components against stem borers could be significantly helpful. Results In this study, the results of field trapping assay and behavioral assay showed the larvae of C.auricilius, one kind of stem borers, could be deterred by rice plant under tilling stage, its main host crop. The profiles of volatiles were compared between rice plants under two different developmental stages, and α-pinene was identified as a key differential component. The repelling activity of α-pinene against C.auricilius was confirmed by Y-tube olfactometer. For illuminating the olfactory recognition mechanism, transcriptome analysis was carried out, and 13 chemosensory proteins (CSPs) were identified in larvae and 19 CSPs were identified in adult of C.auriciliu, which was reported for the first time in this insect. Among these identified CSPs, 4 CSPs were significantly regulated by α-pinene treatment, and CSP8 showed good binding affinity with α-pinene in vitro. Conclusions Overall, C.auricilius could be repelled by rice plant at tilling stage, and our results highlighted α-pinene as a key component in inducing repelling activity at this specific stage and confirmed the roles of some candidate chemosensory elements in this chemo-sensing process. The results in this study could provide valuable information for chemosensory mechanism of C.auricilius and for identification of “push” agent against rice stem borers.

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