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.

This paper retrieved categorical mainland coastline information in the Bohai Rim from 1980, 1990, 2000 and 2010 utilizing remote sensing and GIS technologies and analyzed the characteristics and causes of the spatial–temporal variation over the past 30 years. The results showed that during the research period, the length of the coastline of the Bohai Rim increased continuously for a total increase of 1071.3 km. The types of coastline changed significantly. The amount of artificial coastlines increased continuously and dramatically from 20.4 % in 1980 to 72.2 % in 2010, while the length of the natural coastlines decreased acutely. Areas that had coastlines that changed significantly were concentrated in Bohai Bay, the south and west bank of Laizhou Bay and the north bank of Liaodong Bay. Due to the comprehensive effects of natural and anthropogenic factors, the coastline mainly expanded seaward. Coastal engineering construction were the leading factor in coastal evolution. Furthermore, the reclamation of aquaculture pond, salt field and harbor construction were the top three construction activities. Additionally, the driving force caused coastline change showed significant temporal heterogeneity.