Electrogenetic depolymerization of poly-gamma glutamic acid in Bacillus subtilis biofilms

Gene expression in electroactive bacteria (EAB), which sense electrochemical stimuli and elicit genetic response, can be regulated through electrogenetic methods. Although differential gene expression patterns have been observed in biofilms grown on polarized electrodes, little is known about the molecular mechanisms that sense electrochemical potential and bring about the genetic regulation in response to this potential. Here, we observe that the molecular weight of poly gamma glutamic acid (γ-PGA) produced in Bacillus subtilis PB5760 biofilms changed with the applied electrochemical potential. The application of 0.2 and 0.4 V vs. Ag/AgCl reduced the molecular weight of γ-PGA in the biofilm from 3800 to 4070 kDa at open circuit potential (OCP) to 1040–1590 kDa and 2170–2730 kDa, respectively. Under the same conditions, the relative levels of expression of pgdS, a gene that codes for a γ-PGA-specific endo-hydrolase in cells growing at OCP, 0.2 and 0.4 V vs. Ag/AgCl were 1.12 ± 0.57, 2.74 ± 0.54, 1.61 ± 0.57, respectively, which correlates with the molecular weight reduction. This is the first biotechnological application of electrogenetics for producing γ-PGA with a tunable molecular weight. Results show the feasibility of electrogenetics approach for gene regulation in EAB.