Glucose limitation and glucose uptake rate determines metabolite production and sporulation in high cell density continuous cultures of Bacillus amyloliquefaciens 83

Bacillus amyloliquefaciens spores have been used as the principal ingredient of biocontrol products. However, during the process of spore production, wild-type strains produce poly-gamma-glutamic acid (gamma-PGA), an undesirable byproduct that increases broth viscosity and hinders recovery and drying. This work examined the influence of specific glucose uptake rates (q(Gluc)) in glucose-controlled overflow metabolism. Diverse scenarios, from glucose limitation to glucose sufficiency, were evaluated in continuous cultures to control qGluc. Cell yields of glucose were higher at low qGluc, while the opposing trend was found for gamma-PGA and other overflow metabolic byproducts yields. However, gamma-PGA production was still detectable in cultures with the highest glucose limitation (D = 0.06 h(-1)), even though high sporulation incidence was observed in these cultures. Indeed, in such conditions, nonsporulating vegetative cells seem to maintain glucose overflow metabolism, allowing limited gamma-PGA production. These findings can be used to establish fed-batch culture strategies for high cell density Bacillus amyloliquefaciens cultures where gamma-PGA production (and apparent viscosity) is significantly reduced. This is the first time that the dependence of qGluc on growth, sporulation and carbon overflow metabolism of a spore and biofilm producer, Bacillus amyloliquefaciens strain, has been reported.