TMT-based proteomic analysis of the fish-borne spoiler Pseudomonas psychrophila subjected to chitosan oligosaccharides in fish juice system.

P. psychrophila is implicated in fish spoilage especially under cold storage. In the present study, tandem mass tag (TMT) quantitative proteomic analysis was performed to clarify the molecular mechanism for the inhibitory effect of chitosan oligosaccharides (COS) against P. psychrophila in fish juice system. The MIC and MBC of the COS against P. psychrophila were 6 and 8 mg/mL, respectively. Compared with the untreated control, a total of 370 proteins (163 up-regulated and 207 down-regulated) were identified as differentially expressed proteins (DEPs, >1.5-fold or < 0.67-fold, P < 0.05) in P. psychrophila when exposed to 6 mg/mL COS. Bioinformatics analysis indicated that the DEPs were mainly involved in the cell wall/membrane, cell motility, and electron-transport chain; DNA replication, RNA transcription and translation, posttranslational modifications of proteins; TCA cycle, and the transport and metabolism of amino acid, carbohydrate, and ion. The scanning electron microscope (SEM) and fourier-transform infrared spectroscopy (FT-IR) analysis further validated that cell structure especially the cell wall/membrane was damaged after COS treatment. The results in this study presented an important step toward understanding the response of P. psychrophila cells to COS at the proteome level.

Characterization of a cold-active bacterium isolated from the South Pole "Ice Tunnel".

Extremely cold microbial habitats on Earth (those below -30 °C) are rare and have not been surveyed for microbes as extensively as environments in the 0 to -20 °C range. Using cryoprotected growth media incubated at -5 °C, we enriched a cold-active Pseudomonas species from -50 °C ice collected from a utility tunnel for wastewater pipes under Amundsen-Scott South Pole Station, Antarctica. The isolate, strain UC-1, is related to other cold-active Pseudomonas species, most notably P. psychrophila, and grew at -5 °C to +34-37 °C; growth of UC-1 at +3 °C was significantly faster than at +34 °C. Strain UC-1 synthesized a surface exopolymer and high levels of unsaturated fatty acids under cold growth conditions. A 16S rRNA gene diversity screen of the ice sample that yielded strain UC-1 revealed over 1200 operational taxonomic units (OTUs) distributed across eight major classes of Bacteria. Many of the OTUs were Clostridia and Bacteriodia and some of these were probably of wastewater origin. However, a significant fraction of the OTUs were Proteobacteria and Actinobacteria of likely environmental origin. Our results shed light on the lower temperature limits to life and the possible existence of functional microbial communities in ultra-cold environments.

Response of the aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 to low temperature and zinc oxide nanoparticles stress.

Performance and molecular changes of an aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 have been investigated under different temperatures and ZnO nanoparticles (NPs) exposures. Strain HA-2 removed 95.7% of total nitrogen (TN) and 24.6% of phosphorus at 10 °C, which was attributed to the joint up-regulation of intracellular energy metabolism and ribosome. Moreover, with the increase of ZnO NPs from 0 to 100 mg/L, TN and phosphurs removal efficiencies decreased from 95.7% to 44.5% and 24.6% to 6.8% at 10 °C, respectively, whereas phosphorus removal rate increased from 10.5% to 24.5% at 20 °C. Further transcriptomics and proteomics revealed that significant down-regulation of purine and amino acid metabolisms was the main reason for the inhibitory effect at 10 °C, while the up-regulation of antioxidant pathways and functional genes expressions was responsible for the promoted phosphorus accumulation at 20 °C. This study provides a potential solution for improving biological nutrients removal processes in winter months.

Analysis of amino acid residues involved in the thermal properties of isocitrate dehydrogenases from a psychrophilic bacterium, Colwellia maris, and a psychrotrophic bacterium, Pseudomonas psychrophila.

Monomeric NADP+-dependent isocitrate dehydrogenase (IDH) from a psychrophilic bacterium, Colwella maris, (CmIDH) is a cold-adapted enzyme, whereas that of a psychrotrophic bacterium, Pseudomonas psychrophila, (PpIDH) is mesophilic. However, the amino acid sequence identity of the two IDHs is high (67%). To identify the amino acid residues involved in the differences in their thermal properties, such as optimum temperature and thermostability for activity, six amino acid residues located in the corresponding positions of their regions 2 and 3 were substituted by site-directed mutagenesis, and several thermal properties of the mutated IDHs were examined. CmIDH mutants, CmE538L, CmE596L and CmA741S, substituted at Glu538, Glu596 and Ala741 by the corresponding PpIDH residues of Leu, Leu and Ser, respectively, exhibited higher thermostability than wild-type CmIDH (CmWT). Furthermore, the specific activity of CmE596L and CmA741S was higher than that of CmWT. On the other hand, the corresponding mutants of PpIDH PpL536E, PpL594E and PpS739A were more thermolabile than wild-type PpIDH, and PpL594E had a lower specific activity at temperatures over 45°C. These results suggested that these amino acid residues of CmIDH and PpIDH are involved in their thermal properties.