A marine lipopeptides-producing Bacillus amyloliquefaciens HY2-1 with a broad-spectrum antifungal and antibacterial activity and its fermentation kinetics study

The antagonistic Bacillus amyloliquefaciens HY2-1 was a marine microbiology that was isolated previously from the seabed silt of Beibu Gulf in China by dual culture with Penicillium digitatum. As a continuous study, the present work focused on evaluating the antimicrobial activity, identifying the produced active components, and revealing the fermentation characteristics of B. amyloliquefaciens HY2-1, respectively. It was found that B. amyloliquefaciens HY2-1 exhibited a broad-spectrum antimicrobial activity against the tested seven phytopathogenic fungi and five pathogenic bacteria by producing Bacillus lipopeptides such as fengycin A (C-14 to C-19 homologues) and surfactin (C-14 and C-15 homologues). Morphological observation of P. digitatum under light microscope, scanning electron microscopy, transmission electron microscopy, and fluorescence microscope inferred that B. amyloliquefaciens exerted the antagonistic activity by damaging the fungal cell membrane, thus inhibiting the mycelium growth and sporification of phytopathogenic fungi. As a marine microbiology, our results showed that B. amyloliquefaciens could survive and metabolize even at the culture condition with 110 g/L of NaCl concentration, and the produced antimicrobial compounds exhibited excellent thermostability and acid-alkali tolerance. The dynamic models were further constructed to theoretically analyze the fermentation process of B. amyloliquefaciens HY2-1, suggesting that the synthesis of antimicrobial compounds was coupled with both cell growth and cell biomass. In conclusion, the marine lipopeptides-producing B. amyloliquefaciens HY2-1 showed a promising prospect to be explored as a biocontrol agent for plant disease control of crops and postharvest preservation of fruits and vegetables, especially due to its outstanding stress resistance and the broad-spectrum and effective antagonist on various phytopathogenic fungi.