Diversity of Cultivable Protease-Producing Bacteria in Laizhou Bay Sediments, Bohai Sea, China.

Yan Li,Wei Liu,Chaoya Wu,Jicai Ning,Mingyang Zhou,En Tao Wang,Zhenpeng Zhang,Zhihong Xie

doi:10.3389/fmicb.2017.00405

Abstract

Protease-producing bacteria are widespread in ocean sediments and play important roles in degrading sedimentary nitrogenous organic materials. However, the diversity of the bacteria and the proteases involved in such processes remain largely unknown especially for communities in enclosed sea bays. Here, we investigated the diversity of the extracellular protease-producing bacteria and their protease types in Laizhou Bay. A total of 121 bacterial isolates were obtained from sediment samples in 7 sites and their protease types were characterized. The abundance of cultivable protease-producing bacteria was about 104 CFU g−1 of sediment. Phylogenetic analysis based on 16S rRNA gene sequences suggest that the isolates belonged to 17 genera from 4 phyla including Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes, and mainly dominated by the genera Pseudoalteromonas (40.5%), Bacillus (36.3%), and Photobacterium (5.8%). The diversity and community structure varied among different sampling sites but no significant correlation was observed with soil sediment's characteristics. Enzyme activity and inhibition tests further revealed that all isolates secreted proteases that were inhibited by serine and/or metalloprotease inhibitors, and a smaller proportion was inhibited by inhibitors of cysteine and/or aspartic proteases. Furthermore, all isolates effectively degraded casein and/or gelatin with only a few that could hydrolyze elastin, suggesting that the bacteria were producing different kinds of serine proteases or metalloproteases. This study provided novel insights on the community structure of cultivable protease-producing bacteria near the Yellow River estuary of an enclosed sea bay.

Highlights

Polymeric and particulate materials, which carry abundant organic nitrogen (OrgN), are the main nitrogen sources in marine environments
Protease-producing bacteria play key roles on ecological and biochemical cycles in marine sediments, few studies have been done to understand the diversity of these species and of their extracellular proteases
Out of the 78 protease-producing bacteria isolated from the sediments of the deep South China Sea, 77 isolates belonged to Gammaproteobacteria under Alteromonas, Pseudoalteromonas, Marinobacter, Idiomarina, Halomonas, Vibrio, Shewanella, Pseudomonas, and Rheinheimera; while a single isolate belonged to Firmicutes (Bacillus), and dominated mostly by Alteromonas and Pseudoalteromonas accounting for 34.6 and 28.2% of the total relative abundance, respectively (Zhou et al, 2009)

Summary

Introduction

Polymeric and particulate materials, which carry abundant organic nitrogen (OrgN), are the main nitrogen sources in marine environments. Since proteins comprise the main component of biomass of marine organisms (Thamdrup and Dalsgaard, 2008; Lloyd et al, 2013; Moore et al, 2014), proteaseproducing bacteria are considered as the main degraders of organic nitrogen in the marine environment (Chen et al, 2003; Zhao et al, 2012) These protease-producing bacteria usually secrete extracellular proteases that degrade protein materials, for example, by hydrolyzing the OrgN into peptides and amino acids, with the latter taken up by bacteria for subsequent catabolism (Zhao et al, 2012). A similar community profile was observed in marine sediments of the eutrophied Jiaozhou Bay, China, where 69 protease-producing bacteria belonging to 9 genera from three phyla were isolated, including Bacteroidetes, Firmicutes, and Proteobacteria, in which Photobacterium, Bacillus and Vibrio were the dominant groups, mainly producing serine and/or metalloproteases with relatively low proportions of cysteine proteases (Zhang et al, 2015)

Objectives

Methods

Results