Particle size shapes the prokaryotic microbial communities in mangrove sediments:A case study of Sanya,China

The prokaryotic microbial communities in the sediments play crucial roles in the ecological functions of mangrove ecosystems.Therefore,the environmental factors that affect the structures of these prokaryotic microbial communities could indirectly participate in the regulation of mangrove functions,which is of great value for mangrove studies.The particle size(PS)of soils is recently demonstrated as a key environmental factor for shaping the microbial communities;however,this hypothesis has rarely been tested for mangrove environments.A case study of three tropical mangroves from Sanya,China was performed in this work to assess the influence of PS on the prokaryotic microbial community structures of bacteria,archaea,diazotrophs,and denitrifiers in the sediments.Results showed the variability in the spatial scale and the stability in the temporal scale for the prokaryotic communities,indicating that the tropical mangrove sediments could be a versatile but stable environment.Among the collected environmental factors,PS,salinity,and humidity had the greatest impacts,and PS mostly affected the structures of these prokaryotic communities based on its highest R^2 values of canonical correspondence analysis,Mental test,and linear fitting(p≤0.05).Furthermore,PS was positively correlated with the diversity and abundance of diazotrophic communities and negatively correlated with the abundances of methanogenic communities including Methanobacteriaceae,Methanospirillaceae,Methanoregulaceae,and Methanosaetaceae.Former studies show the increasing trend of PS caused by the rise of sea level and the intensification of human activities.Therefore,our findings indicate that PS could be a potential intermediate that links climate change and human activities with the possible ecological function migration of mangroves;meanwhile,the increase of PS could in turn release the stress of these environmental changes by increasing the abundance and diversity of the diazotrophic community and decreasing the abundances of methanogens.

Enhanced cold active lipase production by metagenomic library recombinant clone CALIP3 with a step-wise temperature and dissolved oxygen level control strategy

A metagenomic library recombinant clone CAPL3, an Escherichia coli strain generated by transformed with metagenomic library from deep-sea sediments, can efficiently produce cold active lipase. The effects of both temperature and dissolved oxygen（DO） on cold active lipase production by batch culture of metagenomic library recombinant clone（CAPL3） from deep-sea sediment were investigated. First, a two-stage temperature control strategy was developed, in which the temperature was kept at 34 ℃ for the first 15 h, and then switched to30 ℃. The cold active lipase activity and productivity reached 315.2 U·ml^-1and 8.08 U·ml^-1·h^-1, respectively,increased by both 14.5% compared to the results obtained with temperature controlled at 30℃. In addition, different DO control modes were conducted, based on the data obtained from the different DO control strategies and analysis of kinetics parameters at different DO levels. A step-wise temperature and DO control strategy were developed to improve lipase production, i.e., temperature and DO level were controlled at 34℃, 30% during 0–15 h;30 ℃, 30% during 15–18 h, and 30 ℃, 20% during 18–39 h. With this strategy, the maximum lipase activity reached 354.6 U·ml^-1at 39 h, which was 28.8% higher than that achieved without temperature and DO control（275.3 U·ml^-1）.