Co-producing lipopeptides and poly-gamma-glutamic acid by solid-state fermentation of Bacillus subtilis using soybean and sweet potato residues and its biocontrol and fertilizer synergistic effects.

A Bacillus subtilis strain B6-1, previously isolated from the rhizosphere of vegetable, selectively produced antibiotics or poly-gamma-glutamic acid (gamma-PGA) in two kinds of liquid media and their co-productions were obtained when using soybean and sweet potato residues in solid-state fermentation. The antibiotics were purified and identified as fengycins. After these residue cultures were introduced, cucumber wilts were effectively suppressed. The introduction also significantly increased the dry weights of roots and shoots of cucumber seedlings, and the roots to shoots ratio, especially at lower nutrition, which indicated the fertilizer synergistic effects. So the product of soybean and sweet potato residues, cultivated with B6-1 co-producing lipopeptides and gamma-PGA, can be expected to be used as both biocontrol agents and fertilizer synergists.