Evaluation of antagonistic activities of Bacillus subtilis and Bacillus licheniformis against wood-staining fungi: In vitro and in vivo experiments

The antifungal activity of bacterial strains Bacillus subtilis EF 617317 and B. licheniformis EF 617325 was demonstrated against sapstaining fungal cultures Ophiostoma flexuosum, O. tetropii, O. polonicum, and O. ips in both in vitro and in vivo conditions. The crude active supernatant fractions of 7 days old B. subtilis and B. licheniformis cultures inhibited the growth of sapstaining fungi in laboratory experiments. Thermostability and pH stability of crude supernatants were determined by series of experiments. FT-IR analysis was performed to confirm the surface structural groups of lipoproteins present in the crude active supernatant. Partial purification of lipopeptides present in the crude supernatant was done by using Cellulose anion exchange chromatography and followed by Sephadex gel filtration chromatography. Partially purified compounds significantly inhibited the sapstaining fungal growth by in vitro analysis. The lipopeptides responsible for antifungal activity were identified by electrospray ionization mass spectrometry after partial purification by ion exchange and gel filtration chromatography. Four major ion peaks were identified as m/z 1023, 1038, 1060, and 1081 in B. licheniformis and 3 major ion peaks were identified as m/z 1036, 1058, and 1090 in B. subtilis. In conclusion, the partially purified lipopeptides may belong to surfactin and iturin family. In vivo analysis for antifungal activity of lipopeptides on wood was conducted in laboratory. In addition, the potential of extracts for fungal inhibition on surface and internal part of wood samples were analyzed by scanning electron microscopy.