Electrofermentation increases concentration of poly -glutamic acid in Bacillus subtilis biofilms

Fluctuations in redox conditions in bioprocesses can alter the end-products, reduce their concentration, and lengthen the process time. Electrofermentation enables rapid metabolic modulation of biosynthesis and allows control of redox imbalances in biofilm-based fermentation processes. In this study, electrofermentation is used to boost the production of the bacterial biopolymer poly-gamma-glutamic acid (gamma-PGA) from Bacillus subtilis ATCC 6051. When compared to control experiments (3.3 +/- 0.99 g L-1), the application of an electrode potential E = 0.4 V versus Ag/AgCl results in a more than two-fold increase in the production of gamma-PGA (9.13 +/- 1.4 g L-1). Using an engineered B. subtilis strain, in which gamma-PGA production is driven by isopropyl beta-d-1-thiogalactopyranoside, electrofermentation improves polymer concentrations from 15.4 +/- 1.5 to 23.1 +/- 1.6 versus g L-1. These results confirm that electrofermentation conditions can be adopted to increase the concentration of gamma-PGA and perhaps other extracellular biopolymers in industrial strains.