Expression and enzymatic characterization of a cold-adapted β-agarase from Antarctic bacterium Pseudoalteromonas sp.NJ21

An agar-degrading bacterium,designated as Pseudoalteromonas sp. NJ21,was isolated from an Antarctic sediment sample. The agarase gene a ga1161 from Pseudoalteromonas sp. NJ21 consisting of a 2 382-bp coding region was cloned. The gene encodes a 793-amino acids protein and was found to possess characteristic features of the Glyco_hydro_42 family. The recombinant agarase(r Aga1161) was overexpressed in Escherichia coli and purified as a fusion protein. Enzyme activity analysis revealed that the optimum temperature and pH for the purified recombinant agarase were 30–40°C and 8.0,respectively. rAga1161 was found to maintain as much as 80% of its maximum activity at 10°C,which is typical of a coldadapted enzyme. The pattern of agar hydrolysis demonstrated that the enzyme is an β-agarase,producing neoagarobiose(NA2) as the final main product. Furthermore,this work is the first proof of an agarolytic activity in Antarctic bacteria and these results indicate the potential for the Antarctic agarase as a catalyst in medicine,food and cosmetic industries.     

Purification and characterization of a new thermostable κ-carrageenase from the marine bacterium Pseudoalteromonas sp. QY203

A new extracellular κ-carrageenase, namely CgkP, 34.0 kDa in molecular weight, was purified from Pseudoalteromonas sp. QY203. CgkP showed relatively high activity at acidities ranging from pH6.0 to pH9.0 and temperatures ranging from 30℃ to 50℃ with the highest activity at 45℃ and pH7.2. Sodium chloride increased its activity markedly, and KCl increased its activity slightly. The divalent and trivalent metal ions including Cu2+ , Ni2+ , Zn2+ , Mn2+ , Al3+ and Fe3+ significantly inhibited its activity, while Mg2+ did not. CgkP remained 70% of original activity after being incubated at 40℃ for 48 h, and remained 80% of the activity after being incubated at 45℃ for 1 h. It exhibited endo-κ-carrageenase activity, mainly depolymerizing the κ-carrageenan into disaccharide and tetrasaccharide. CgkP was more thermostable than most of previously reported κ-carrageenases with a potential of being used in industry.     

Characterization of Fe(Ⅲ)-Reducing Enrichment Cultures and Isolation of Enterobacter sp.Nan-1 from the Deep-Sea Sediment,South China Sea

To characterize the Fe(Ⅲ)-reducing bacteria, enrichment cultures were initiated by inoculating deep-sea sediment from the South China Sea(SCS) into the media with hydrous ferric oxide(HFO) as the sole electron acceptor. As indicated by Meta 16 S rDNA Amplicon Sequencing, the microorganisms related to Fe(Ⅲ)-reduction in the enrichment cultures were mainly Shewanella and Enterobacter. A new facultative Fe(Ⅲ)-reducing bacterium was obtained and identified as Enterobacter sp. Nan-1 based on its 16 S rRNA gene sequence and physiological characterizations. Enterobacter sp. Nan-1 was not only a mesophilic bacterium capable of reducing HFO with a wide range of salinity(4, 34, 40, 50 and 60 g L~(-1)) efficiently, but also a piezotolerant bacterium that can proceed Fe(Ⅲ)-reduction sustainedly at hydrostatic pressures between 0.1 and 50 MPa using glucose and pyruvate as carbon source. Furthermore, the geochemical characteristics of deep-sea sediment indicated that the microbial metabolism and iron reduction both remain active in the well-developed Fe(Ⅲ)-reducing zone where the strain Nan-1 was obtained. To our knowledge, Enterobacter sp. Nan-1 could serve as a new applicative Fe(Ⅲ)-reducing bacterium for future investigation on the iron biogeochemical cycle and diagenetic process of organic matter in the deep-sea environment.