Biofilm formation by a Bacillus subtilis strain that produces γ-polyglutamate

The extracellular matrix produced by Bacillus subtilis B-1, an environmental strain that forms robust floating biofilms, was purified, and determined to be composed predominantly of gamma-polyglutamate (gamma-PGA), with a molecular mass of over 1000 kDa. Both biofilm formation and gamma-PGA production by B. subtilis B-1 increased with increasing Mn2+ or glycerol concentration. gamma-PGA was produced in a growth-associated manner in standing culture, and floating biofilms were formed. However, gamma-PGA was produced in a non-growth-associated manner in shaking culture conditions. When B. subtilis B-1 was grown in a microaerated culture system, floating biofilm formation and gamma-PGA production were significantly retarded, suggesting that oxygen depletion is involved in the initial steps of floating biofilm formation in standing culture. Proteomic analysis of membrane proteins demonstrated that flagellin, oligopeptide permease and Vpr protease precursor were the major proteins produced by cells in a floating biofilm and a colony.