Study On Polyphasic Taxonomy And Cold-adapted Mechanism Of Antarctic Marine Bacterium Poseidonibacter Antarcticus SM1702~T

The ocean is the largest ecosystem on the earth.About 71%of the earth surface is covered by the ocean,which contains a large number of microbial resources.The unique environmental characteristics of the Antarctic sea,such as low temperature,high radiation and high salinity,determines the novelty and diversity of the microorganisms living in it.However,there are still many microbial resources in Antarctica that have not been developed and utilized.Psychrotrophs that could grow at low temperature are widespread in the Antarctic region.How psychrotrophs adapt to low temperature is now a hot topic of microbial research.In this thesis,a novel bacterium isolated from Antarctic intertidal sediment was taken as the object of study,and its taxonomic position was identified through the polyphasic taxonomy research.In addition,its cold-adapted mechanism was further investigated.The following results were obtained:1.Polyphasic taxonomy of Antarctic marine bacterium Poseidonibacter antarcticus SM1702TChe Antarctic sea is one of the most special geographical environments on the earth,and contains a large amount of precious microbial resources.Strain SM1702T isolated from the Arctic Antarctic sediment sample by our laboratory is suspected to be a representative of a new species.Cells of strain SM1702T were Gram-negative,aerobic,and flagellated coccoid.Cells grew at 0-30?(optimum at 25?),at pH 5.5-8.0(optimum at 7.5)and with 0.5-5.5%NaCl(w/v,optimum with 1.0%).Major cellular fatty acids(>5%of total fatty acids)are summed feature 3(C16:1?7c and/or C16:1?6c),summed feature 8(C18:1?7c and/or C18:1?6c),Ci6:o and summed feature 2(Ci4:o 3-OH and/or iso-C16:1 I)-Polar lipids comprise phosphatidylethanolamine and phosphatidylglycerol.The genomic DNA G+C content of the type strain is 27.1%.Strain SM1702T was affiliated with the genus Poseidonibacter,sharing the highest 16S rDNA sequence similarity(95.6%)with the type strain of Poseidonibacter lekithochrous.The phylogenetic tree based on 16S rRNA gene sequence showed that strain SM1702T was clustered with Poseidonibacter lekithochrous,and they formed an independent evolutionary branch.Based on the polyphasic evidence presented in this study,strain SM1702T represents a novel Poseidonibacter species,for which the name Poseidonibacter antarcticus sp.nov.is proposed.The type strain is SMV1702T(=CCTCC AB 2019008T=MCCC 1K03471T=KCTC 62796T).2.Cold-adapted mechanism of Antarctic marine bacterium Poseidonibacter antarcticus SM1702TIn order to study the cold-adapted mechanism of the Antarctic marine bacterium Poseidonibacter antarcticus SM1702T,the transcriptomes and proteomes were sequenced and compared when this strain was cultured at high and low temperatures.The results showed that up-regulated proteins of strain SM1702T were mainly related to the material transport pathway of the cell membrane.This indicates that maintenance of membrane protein functions is the key to cold-adaptation of this strain.By increasing the amounts of transporters,bacteria can resist the pressure of material transport impairment caused by low temperature and improve the ability to transport and acquire nutrition at the low temperature.The physiological and biochemical characteristics of strain SM1702T at different temperatures were further investigated.the generation time of the strain grown at 0?was 12.2 times more than that at 25?.Activities of two intracellular enzymes of strain SM1702T were determined at different temperatures.The results showed that from 25?to 0?,the activity of isocitrate dehydrogenase(IDH)decreased by 1.6 times,and the activity of phosphoglycerate kinase(PGK)decreased by 1.4 times.The decrease of enzyme activity at low temperature was much less than that of growth rate.This suggests that the decrease of enzyme reaction rate is not the main factor limiting the growth of bacteria at low temperature.The membrane fatty acid composition of strain SM1702T cultured at different temperatures were determined.The results showed that the contents of monounsaturated fatty acids,branched fatty acids and short chain fatty acids increased at low temperature to maintain the membrane fluidityIn conclusion,our results implied that impairment of the membrane proteins function caused by low temperature is the main threat to the strain SM1702T living at cold environment.This strain may thrive by changing the membrane fatty acid compositions and increasing the transporter numbers to maintain the normal transport function at low temperature.