Isolation and identification of a keratinase-producing strain of Aeromonas bacterium

Abstract:

Not all of Aeromonas species were pathogenic, and some bacteria of this genus were found to have important utilization value in recent years. Effective utilization of discarded feather by microorganism-decomposing method could meet the requirements of environment and Low-carbon economy. However, screening and evaluation of more microbe resources should be favourable for solving the thorny problem on poor efficiency and low speed of biodegradation. In the study, keratinase-producing strains were isolated from decaying feather using feather selective medium, casein plate and enzyme activity assay of keratinase in fermentation liquid of feather. The morphological observation of cell and colony, sugar fermentation experiments, Gram stain, PCR and sequence analysis of 16S rDNA were performed for taxonomic classification. The strain named FD41 with the highest relative keratinase activity (RKA, viz. the ratio of keratinase activity unit to A₆₀₀ value of feather fermentation liquid) of 3.864 U/OD₆₀₀ was isolated. The BLAST using the 16S rDNA sequence (GenBank accession No. HM587254) of FD41 showed that the first 100 sequences, all from Aeromonas, shared high homology to HM587254 with 99% identity. According to the results of taxonomic classification, the strain FD41 was identified as an Aeromonas bacterium. This is the first report on keratinase-producing strain of Aeromonas bacterium. The measurement values of keratinase activity of fermentation liquid were found to be influenced signally by cell proliferation. The different strains and inoculation amounts resulted in very distinct proliferation curves of bacterium in liquid medium. These results suggested that the RKA was appropriate index and equalizing inoculation amount was prerequisite for screening and identifying of strains with high enzyme activity at same condition of liquid culture.