Polyphasic Taxonomy Of Fluviibacterium Aquatile SM1902T And Effect Of Starvation Treatment On The Variation Of Bacterial Community In The Open Ocean Surface Seawater

A huge number of microorganisms live in the ocean.At present,most of them have not been isolated,cultured or identified.The estuary ecosystem is one of the typical marine ecosystems near the shore.The estuary is located at the junction between the ocean and fresh water.The unique natural environment and frequent human activities increase its microbial diversity.New microbial species are often found in this area.For marine microorganisms,low nutrient concentration is a common environmental factor that limits their growth.When under starvation stress,some microorganisms can respond to environmental changes by regulating gene expression and changing phenotypes,while some microorganisms will be in a dormant state to survive.When nutrients are reintroduced,some microorganisms may recover and grow.However,it is still unclear which kind of microbial groups could survive during long time starvation and respond quickly when nutrients are subsequently available in the open ocean surface seawater.In this thesis,the strain SM1902T isolated from the sediment sample of the Jia River estuary in Yantai was taxonomically characterized using a polyphasic taxonomy approach.Meanwhile,high-throughput sequencing of 16S rRNA gene was used to analyze the variation of bacterial community in the surface seawater from Mariana Trench area after long time starvation and subsequent nutrient input.1.Polyphasic taxonomy of the strain SM1902T isolated from the sediment sample of the Jia River estuary in YantaiThe strain SM1902T was isolated from the sediment sample of the Jia River estuary,Yantai,China.Cells are Gram-reaction-negative,aerobic,non-flagellated rods or ovoid rods(1.5-4.6 ?m long and 1.3-2.6 ?m wide).It grew at 10-37?(optimum,25-30?),pH 6.0-10.0(optimum,pH 7.0)and with 0.5-13.0%(w/v)NaCl(optimum,2.5%).The strain SM1902T is oxidase-and catalase-positive.Cells are positive for hydrolysis of Tweens 20,60 and 80,but negative for hydrolysis of Tween 40,DNA,starch or casein.Nitrate is reduced to nitrite.Bacteriochlorophyll a is not produced.Cells of strain SM1102T are resistant to gentamicin.The predominant cellular fatty acids is summed feature 8(C18:1 ?7c and/or C18:1?6c)The major polar lipids are phosphatidylcholine,phosphatidylglycerol,phosphatidylethanolamine,an unidentified aminolipid and an unidentified lipid.The sole respiratory quinone is ubiquinone-10.Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SM1902T constituted a separated lineage within the family Rhodobacteraceae and was closely related with Meridianimarincocus roseus TG-679T and Phycocomes zhengii LMIT002T with 96.1%and 94.3%16S rRNA gene sequence similarities.The in silico DNA-DNA hybridization(isDDH)values between strain SM1902T and M.roseus TG-679T and P.zhengii LMIT002T are 19.6%and 19.5%,respectively,and the average nucleotide identity(ANI)values are 76.1%and 74.2%,respectively.In phylogenetic trees based on the 550 single-copy orthologous clusters and whole-genome sequences,strain SM1902T also clustered with M.roseus TG-679T and P.zhengii LMIT002T within the family Rhodoacteraceae.The genomic DNAG+C content of strain SM1902T is 58.2 mol%.Based on the polyphasic data obtained in this study,the strain SM1902T is considered to represent a novel species in a new genus within the family Rhodobacteraceae,for which the name Fluviibacterium aquatile gen.nov.,sp.nov.is proposed.The type strain is SM1902T(=KCTC 72045T=MCCC 1K03596T=CCTCC AB 2018346T).2.Effect of Starvation Treatment on the Variation of Bacterial Community in the Open Ocean Surface SeawaterAn extreme starvation stress was created by keeping the surface seawater from the Mariana Trench area in the dark for 24 months at room temperature.Then two types of nutrients were added.High-throughput sequencing of 16S rRNA gene was used to analyze the variation of bacterial community after long time starvation and subsequent nutrient input.The main groups of bacteria in the in situ seawater sample before starvation treatment were Alphaproteobacteria(37.47%),Gammaproteobacteria(24.89%),Oxyphotobacteria(21.69%),Bacteroidia(6.59%),Deltaproteobacteria(1.76%)and Acidimicrobiia(1.63%).After 24 months of starvation treatment,the main bacterial groups were Alphaproteobacteria(67.18%),Gammaproteobacteria(19.37%),Campylobacteria(2.34%),Acidimicrobiia(1.77%),Bacteroidia(1.76%),Deltaproteobacteria(1.73%),Dehalococcoidia(1.05%)and Actinobacteria(1.04%).After 24 months of starvation treatment,the relative abundance of Alphaproteobacteria,Gammaproteobacteria,Bacteroidia,Deltaproteobacteria and Acidimicrobiia was still relatively high(>1%).Among them,the relative abundance of Alphaproteobacteria increased significantly,from 37.47%to 67.18%.The number of Oxyphotobacteria dropped to almost 0.In addition,the relative abundance of Campylobacteria,Dehalococcoidia and Actinobacteria increased from 0.08%,0.48%and 0.64%to 2.34%,1.05%and 1.04%,respectively.It showed that the microbial community composition changed significantly after starvation treatment.After 24 months of starvation treatment,there were 6 dominant genera,Algiphilus,Hyphomicrobium,Nitratireductor,Parvibaculum,Sinimarinibacterium and Sulfurovum.The relative abundance of these genera after starvation was more than 1%,which was much higher than that in situ(0%-0.08%).Analysis of the Tara oceans dataset indicated that three out of the above six genera,Nitratireductor,Sulfurovum and Parvibaculum are widely distributed in the global surface seawaters.After the addition of two kinds of nutrients,Alphaproteobacteria,Gammaproteobacteria,Deltaproteobacteria and Bacteroidia were the main starvation survival bacteria responding to nutrients input.The dominant genera were Algiphilus,Alteromonas,Arenibacter,Candidatus Berkiella,Hyphomicrobium,Idiomarina,Labrenzia,Marinobacter,Muricauda,Nitratireductor,Phaeodactylibacter,Polycyclovorans,Ruegeria,Sagittula,Spittittula and Sulfurovum.Among them,Algiphilus,Hyphomicrobium,Nitratireductor and Sulfurovum were the dominant genera both in the sample after starvation treatment and in those adding nutrients,indicating that they can maintain high abundance when nutrients are scarce and sufficient.Analysis of the Tara oceans dataset showed that nine of the sixteen dominant genera responding to nutrients after starvation treatment are widely distributed in the global surface seawaters.They are Alteromonas,Idiomarina,Labrenzia,Marinobacter,Muricauda,Nitratireductor,Ruegeria,Sagittula and Sulfurovum.In this thesis,a polyphasic taxonomic study was conducted on the strain SM1902T isolated from the sediment sample of the Jia River Estuary in Yantai,and based on the results,the strain SM1902T was identified as a representative of a novel species in a new genus within the family Rhodobacteraceae.Meanwhile,the variation of bacterial community in the open ocean surface seawater during long-term starvation and subsequent nutrient input was revealed,and about 50%of the dominant bacterial genera were found to be widely distributed in the global surface seawaters.