Expression of essential genes for biosynthesis of antimicrobial peptides of Bacillus is modulated by inactivated cells of target microorganisms

Certain Bacillus strains are important producers of antimicrobial peptides with great potential for biological control. Antimicrobial peptide production by Bacillus amyloliquefaciens P11 was investigated in the presence of heat-inactivated cells of bacteria and fungi. B. amyloliquefaciens P11 exhibited higher antimicrobial activity in the presence of inactivated cells of Staphylococcus aureus and Aspergillus parasiticus compared to other conditions tested. Expression of essential genes related to biosynthesis of the antimicrobial peptides surfactin (sfp), iturin A (lpa-14 and ituD), subtilosin A (sboA) and fengycin (fenA) was investigated by quantitative real-time PCR (qRT-PCR). The genes lpa-14 and ituD were highly expressed in the presence of S. aureus (inactivated cells), indicating induction of iturin A production by B. amyloliquefaciens P11. The other inducing condition (inactivated cells of A. parasiticus) suppressed expression of lpa-14, but increased expression of ituD. A twofold increase in fenA expression was observed for both conditions, while strong suppression of sboA expression was observed in the presence of inactivated cells of S. aureus. An increase in antimicrobial activity was observed, indicating that synthesis of antimicrobial peptides may be induced by target microorganisms.