Characterization of a multifunctional feather-degrading Bacillus subtilis isolated from forest soil

In this study, we isolated and characterized a novel feather-degrading bacterium that shows keratinolytic, antifungal and plant growth-promoting activities. A bacterium S8 was isolated from forest soil and confirmed to belong to Bacillus subtilis by BIOLOG system and 16S rRNA gene analysis. The improved culture conditions for the production of keratinolytic protease were 0.1% (w/v) sorbitol, 0.3% (w/v) KNO₃, 0.1% (w/v) K₂HPO₄, 0.06% (w/v) KH₂PO₄ and 0.04% (w/v) MgCl₂·6H₂O (pH 8.0 and 30°C), respectively. In the improved medium containing 0.1% (w/v) feather, keratinolytic protease production was around 53.3 ± 0.3 U/ml at 4 day; this value was 10-fold higher than the yield in the basal feather medium (5.3 ± 0.1 U/ml). After cultivation for 5 days in the improved medium, intact feather was completely degraded. Feather degradation resulted in free -SH group, soluble protein and amino acids production. The concentration of free -SH group in the culture medium was 15.5 ± 0.2 μM at 4 days. Nineteen amino acids including all essential amino acids were produced in the culture medium; the concentration of total amino acid produced was 3360.4 μM. Proline (2809.9 μM), histidine (371.3 μM) and phenylalanine (172.0 μM) were the major amino acids released in the culture medium. B. subtilis S8 showed the properties related to plant growth promotion: hydrolytic enzymes, ammonification, indoleacetic acid (IAA), phosphate solubilization, and broad-spectrum antimicrobial activity. Interestingly, the strain S8 grown in the improved medium produced IAA and antifungal activity, indicating simultaneous production of keratinolytic and antifungal activities and IAA by B. subtilis S8. These results suggest that B. subtilis S8 could be not only used to improve the nutritional value of feather wastes but also is useful in situ biodegradation of feather wastes. Furthermore, it could also be a potential biofertilizer or biocontrol agent applicable to crop plant soil.