Abstract
Although protease-producing bacteria are key players in the degradation of organic nitrogen and essential for the nitrogen recycling in marine sediments, diversity of both these bacteria and their extracellular proteases is still largely unknown. This study investigated the diversity of the cultivable protease-producing bacteria and their extracellular proteases in the sediments of the eutrophied Jiaozhou Bay, China through phylogenetic analysis and protease inhibitor tests. The abundance of the cultivable protease-producing bacteria was up to 104 cells/g in all six sediment samples. The cultivated protease-producing bacteria mostly belonged to the phyla Proteobacteria and Firmicutes with the predominant genera being Photobacterium (39.4%), Bacillus (25.8%), and Vibrio (19.7%). Protease inhibitor tests revealed that extracellular proteases secreted by the bacteria were mainly serine proteases and/or metalloproteases with relatively low proportions of cysteine proteases. This study represents the first comprehensive analysis on the diversity of protease-producing bacteria and their extracellular proteases in sediments of a eutrophic bay.
Highlights
Organic matters deposited at the sea floor, mostly in the polymeric and particulate forms, serve as the main nitrogen sources in sediments (Thamdrup and Dalsgaard, 2008)
Screening of Extracellular Protease-producing Bacteria from Sediments There were a number of colonies appearing on the screening plates of the 10−1–10−3 diluted samples after cultivation at 15◦C for 2–5 days
There was no obvious difference in the richness of the cultivable protease-producing bacteria among the stations the Organic carbon (OrgC) and OrgN contents and the C/N ratios in these stations were different
Summary
Organic matters deposited at the sea floor, mostly in the polymeric and particulate forms, serve as the main nitrogen sources in sediments (Thamdrup and Dalsgaard, 2008). As proteins constitute large fractions of marine organic matters (Wakeham et al, 1997; Thamdrup and Dalsgaard, 2008; Lloyd et al, 2013; Moore et al, 2014), proteaseproducing bacteria are recognized as key players in the microbial degradation of SON (Herbert, 1999; Zhao et al, 2008, 2012; Chen et al, 2009; Zhou et al, 2009) They secrete extracellular proteases to hydrolyze complex proteinaceous substances into small peptides and amino acids suitable for cellular uptake (Zhao et al, 2008, 2012), initiating the mineralization of SON and driving the nitrogen cycle in marine ecosystem. Despite of their ecological and biogeochemical importance, there are only few studies to date investigating the diversity of sedimentary proteaseproducing bacteria and their extracellular proteases. Olivera et al (2007) screened 19 proteaseproducing bacteria from sub-Antarctic sediments and found them be affiliated with the genera
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