Isolation and identification of a protease-producing bacterium from abalone intestines and its application for...

The gastrointestinal tracts of aquatic animals provide a unique environment for microbial growth. Proteases derived from microorganisms in aquatic taxa are particularly valuable owing to their stability under various temperature and salinity conditions. The aim of this study was to isolate and identify protease-producing bacteria from the intestines of abalone (Haliotis discus hannai) and to evaluate their potential applicability to fishery waste degradation. Specifically, bacteria with high protease activity were isolated from the abalone intestine and identified through 16S rRNA sequencing, followed by the optimization of culture conditions for protease production using response surface methodology (RSM). In total, 15 bacteria were isolated from the intestines of abalone, including six bacteria with protease activity. Among these, T14 showed the highest protease activity at 2.42 ± 0.19 units/mL and was selected for protease production. T14 displayed 99.71% similarity to Vibrio fluvialis NBRC 103150. The optimal culture conditions were pH 7.85, 29.49 °C, and 2.69% NaCl, as determined through RSM modeling. The predicted and validated protease activities were 3.20 and 3.19 ± 0.12 units/mL, respectively. PMSF showed the strongest inhibition, suggesting that strain T14 mainly exhibited serine protease-like activity. The crude enzyme from strain T14 was applied to representative fishery waste materials, including fish skin, bones and intestines. SDS-PAGE analysis showed decreased intensities of several protein bands and the appearance of lower-molecular-weight bands after treatment, indicating partial protein degradation. These results suggest that the crude enzyme from strain T14 has potential for the biological pretreatment and partial degradation of fishery waste materials.