Diversity of protease-producing bacteria in the Bohai Bay sediment and their extracellular enzymatic properties

Protease-producing bacteria play key roles in the degradation of organic nitrogen materials in marine sediments. However, their diversity, production of proteases and other extracellular enzymes, even in situ ecological functions remain largely unknown. In this study, we investigated the diversity of cultivable extracellular protease-producing bacteria in the sediments of the Bohai Bay. A total of 109 bacterial isolates were obtained from the sediments of 7 stations. The abundance of cultivable protease-producing bacteria was about 104 CFU/g of sediment in all the samples. Phylogenetic analysis based on 16S rRNA gene sequences classified all the isolates into 14 genera from phyla Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria, with Pseudoalteromonas (63/109, 57.8%), Bacillus (9/109, 8.2%), Sulfitobacter (8/109, 7.3%) and Salegentibacter (6/109, 5.5%) as the dominant taxa. Enzymatic inhibition tests indicated that all the tested isolates produced serine and/or metalloprotease, with only a small proportion producing cysteine and/or aspartic proteases. Several extracellular enzyme activities, including alginase, lipase, amylase and cellulose, and nitrate reduction were also detected for strains with higher protease activities. According the results, the protease-producing bacteria could also be participate in many biogeochemical processes in marine sediments. Our study broadened understanding and knowledge on the potential ecological functions of protease-producing bacteria in marine sediments.