Signaling herbicide toxicity in Pseudomonas via quorum sensing

With the increase in the human population, agriculture tends to increase its productivity to meet this demand, making the insertion of agrochemicals a common practice. The increased use of herbicides causes environmental contamination and selective pressure on microbiomes. Environmental contamination can be minimized by microbiological degradation of herbicides through selected strains. New lines of research indicate the potential for greater efficiency in the degradation of xenobiotic compounds, even absent from the isolation site, through the gene regulation of microbial consortia behavior and quorun sensing (QS) signaling molecules organized in biofilms. Thus, this work aimed to evaluate the association between QS signaling molecules and biofilm formation, as bacterial responses to herbicide toxicity, which may open the possibility of controlling gene expression by chemical signals in bacterial consortia. The strain Pseudomonas fluorescens CMA55 was used, collected from the biofilm of water storage tanks used to wash herbicide containers. The treatments were performed with herbicide Heat® (active ingredient saflufenacil), present in the tank, and with Roundup Transorb R® (active ingredient glyphosate) absent from the isolation site, to evaluate the effect of previous selective pressure on bacterial responses. Herbicide tolerance tests, bacterial growth curve, cell viability and bacterial biofilm growth analysis were performed in cell culture supplemented with variations in the concentration used in the field of herbicides. None of the treatments inhibited the growth of P. fluorescens, indicating that this strain has tolerance mechanisms for the herbicide that exerted selective pressure in the isolation environment, as well as for the one that did not. There was a significantly greater growth of bacterial culture in the presence of herbicide Heat in relation to Roundup, except for the concentration equivalent to 50x. At this concentration, viability data indicated that Heat was more toxic, unlike other concentrations. The CMA55 strain demonstrated the ability to produce biofilm in quantities inversely proportional to the viability. The data obtained showed that none of the treatments could inhibit the growth of P. fluorescens CMA55, since they did not show significant differences compared with controls. The highest biofilm production was observed in the doses of herbicides with the highest toxicity, according to the viability data, which may indicate the relationship of this structure in the toxicity response system. Therefore, the relationship between QS and biofilms in this experimental model should be studied.