Electrolysis Environment Affected the Expression of Conjugative Transfer Relevant Genes
Transcriptome enrichment analysis showed that 1171 genes of the donor bacteria and 560 genes of the recipient bacteria were up-expressed under the electrolysis stimulation in comparison to that of the control, respectively. The contact between bacteria is a premise for the plasmid-mediated conjugation. The flagella and pilus exerted important role in driving cell-cell contact. The flagella involving in locomotion can increase the encounter probability of bacteria in environment. As for the pilus, they exert a vital role in the adhesion between bacteria. Especially, sex pilus can develop into the conjugation bridge which allows the ARG-carrying plasmid to shuttle between bacterial cells. Therefore, flagella and pilus are important in determining the occurrence of plasmid-mediated conjugation. Zhang et al. found that copper nanoparticles promoted the RP4 plasmid-mediated conjugation through up-regulating the expression of genes relating to the flagella and pilus assembly. In another study, when the bacteria were exposed to an agricultural fungicide namely prochloraz, the flagella and pilus regulatory genes were also up-regulated, which increased the conjugation frequency. Similarly, in our study, the expression of genes annotated as flagella or pilus assembly was significantly enhanced under the electrolysis stimulation. Cell communication referring to the phenomenon signal transmission between adjacent cells through chemical molecules, is essential for plasmid-mediated conjugation. Here, the expression of genes with the function of cell communication were dramatically increased under the electrolysis stimulation.Plasmid-mediated conjugation needs cell membrane transporters as carrier. Studies have demonstrated that some emerging contaminants, such as trichloromethane, dichloroacetonitrile, triclosan, sertraline, duloxetine, fluoxetine, and bupropion could facilitate the plasmid-mediated conjugation via promoting the expression of outer membrane porin regulatory genes. The similar phenomenon was also found in this study. Specifically, for the donor bacteria E. coli, the electrolysis stimulation up-regulated the expression of outer membrane porin regulatory genes bamA, ompA, ompC, ompF, ompW, ompT and slyB, prophage lipoprotein gene borD, murein lipoprotein gene lpp, lipopolysaccharide assembly protein gene lptD, osmotically-inducible lipoprotein gene osmB, and nucleoside-specific channel-forming protein gene tsx. Similar results were also found in the recipient bacteria P. putida. Interestingly, in our study, the expression of ATP synthesis related genes atpA, atpB, atpC, atpF, atpG, atpH, and pykA was found to be promoted by the electrolysis stimulation . This is because the plasmid-mediated conjugative transfer is an active transport that requires ATP for supplying energy. However, it is still not known that whether the electrolysis stimulation affects energy metabolism or conjugation first.