Production of poly‐gamma‐glutamic acid and spore formation in Bacillus velezensis 83 are affected by acidic growing conditions and glucose uptake rate

Abstract

AbstractBACKGROUNDBacillus velezensis 83 is a biocontrol agent and plant growth promoting bacteria that produces antifungal compounds (surfactin and bacilomycin D), plant growth stimulation metabolites such as acetoin and butanediol and the polymer poly‐gamma‐glutamic acid (γ‐PGA), which is essential for bacterial plant colonization. Bacillus sporulation is an important trait in order to obtain long shelf‐life formulations for biocontrol purposes. γ‐PGA production and sporulation are closed‐related processes controlled by glucose availability and modulated by quorum sensing. High spore production (and its recovery) in B. velezensis 83 cultures is limited by the high viscosity oxygen‐limited broths resulting from γ‐PGA accumulation. This work studied the influence of acidic growing conditions and glucose specific uptake rate on growth, quorum sensing‐related metabolites production and sporulation of B. velezensis 83.RESULTSIn batch cultures developed at pH = 5, no bacterial sporulation was detected and quorum sensing related metabolites as γ‐PGA (not detected) and surfactin and bacillomycin were significantly decreased. Instead, acetoin and butanediol were the main products. In contrast, in continuous cultures developed at pH = 5, spores were detected at D = 0.06 h−1. The results indicate that sporulation at pH = 5 is not inhibited by affectations on quorum sensing signals but could be due to a low availability/transport of energy sources (i.e., glucose or acetoin/butanediol) or an affectation on Rap‐Phr system.CONCLUSIONThe findings in this study allow to establish a two‐stage process for Bacillus velezensis 83 spore production: bacterial growth at pH = 5 and sporulation at pH = 6.8. © 2023 Society of Chemical Industry (SCI).