Studies on the role of marine bacteria in the upwelling ecosystem——Ⅰ.Bacterial biomass in the upwelling regions

-Six cruises were carried out off the south bank of Fujian - Taiwan during the period of December 21, 1987 to November 15, 1988 to estimate the contribution of bacterial biomass carbon (BBC) to the totai particulate organic pools using epifluorescent microscopic technique. The results show that the standing crop of bacteria fluctuated from 0. 95 to 66. 60 mg /m3 (dry weight). Upwelling phenomena appeared in the region around Nanpeng Island in summer while in the region of Waixie in all seasons. The average value of BBC was 27. 60(±6. 08)mg/m3and 21. 32 (±2. 34) mg/m3 respectively. The seasonal and spatial distribution is discussed in relation to environmental factors as well as upwelling phenomena. The role of bacteria in the flow of material and energy in the upwelling ecosystem is emphasized.

Analysis of cultivable aerobic bacterial community composition and screening for facultative sulfate-reducing bacteria in marine corrosive steel

Anaerobic, aerobic, and facultative bacteria are all present in corrosive environments. However, as previous studies to address corrosion in the marine environment have largely focused on anaerobic bacteria, limited attention has been paid to the composition and function of aerobic and facultative bacteria in this process. For analysis in this study, ten samples were collected from rust layers on steel plates that had been immersed in seawater for diff erent periods (i.e., six months and eight years) at Sanya and Xiamen, China. The cultivable aerobic bacterial community structure as well as the number of sulfate-reducing bacteria (SRB) were analyzed in both cases, while the proportion of facultative SRB among the isolated aerobic bacteria in each sample was also evaluated using a novel approach. Bacterial abundance results show that the proportions are related to sea location and immersion time;abundances of culturable aerobic bacteria (CAB) and SRB from Sanya were greater in most corrosion samples than those from Xiamen, and abundances of both bacterial groups were greater in samples immersed for six months than for eight years. A total of 213 isolates were obtained from all samples in terms of CAB community composition, and a phylogenetic analysis revealed that the taxa comprised four phyla and 31 genera. Bacterial species composition is related to marine location;the results show that Firmicutes and Proteobacteria were the dominant phyla, accounting for 98.13% of the total, while Bacillus and Vibrio were the dominant genera, accounting for 53.06% of the total. An additional sixfacultative SRB strains were also screened from the isolates obtained and were found to encompass the genus Vibrio (four strains), Staphylococcus (one strain), and Photobacterium (one strain). It is noteworthy that mentions of Photobacterium species have so far been absent from the literature, both in terms of its membership of the SRB group and its relationship to corrosion.

Phylogenetic diversity of dimethylsulfoniopropionate-dependent demethylase gene dmdA in distantly related bacteria isolated from Arctic and Antarctic marine environments

Dimethylsulfoniopropionate(DMSP) is mainly produced by marine phytoplankton as an osmolyte, antioxidant,predator deterrent, or cryoprotectant. DMSP is also an important carbon and sulfur source for marine bacteria.Bacteria may metabolize DMSP via the demethylation pathway involving the DMSP demethylase gene(dmdA) or the cleavage pathway involving several different DMSP lyase genes. Most DMSP released into seawater is degraded by bacteria via demethylation. To test a hypothesis that the high gene frequency of dmdA among major marine taxa results in part from horizontal gene transfer(HGT) events, a total of thirty-one bacterial strains were isolated from Arctic Kongsfjorden seawater in this study. Analysis of 16S rRNA gene sequences showed that,except for strains BSw22118, BSw22131 and BSw22132 belonging to the genera Colwellia, Pseudomonas and Glaciecola, respectively, all bacteria fell into the genus Pseudoalteromonas. DmdA genes were detected in five distantly related bacterial strains, including four Arctic strains(Pseudoalteromonas sp. BSw22112, Colwellia sp.BSw22118, Pseudomonas sp. BSw22131 and Glaciecola sp. BSw22132) and one Antarctic strain(Roseicitreum antarcticum ZS2–28). Their dmdA genes showed significant similarities(97.7%–98.3%) to that of Ruegeria pomeroyi DSS–3, which was originally isolated from temperate coastal seawater. In addition, the sequence of the gene transfer agent(GTA) capsid protein gene(g5) detected in Antarctic strain ZS2–28 exhibited a genetically closely related to that of Ruegeria pomeroyi DSS–3. Among the five tested strains, only Pseudomonas sp. BSw22131 could grow using DMSP as the sole carbon source. The results of this study support the hypothesis of HGT for dmdA among taxonomically heterogeneous bacterioplankton, and suggest a wide distribution of functional gene(i.e., dmdA) in global marine environments.

Growth of marine bacteria and ammonium regeneration from substrates in different C:N ratios

Natural assemblages of marine bacteria were chosen in a batch culture experiments. The impact of varying nitrogen substrate concentrations and the substrate C：N ratios （C：Ns） on the bacterial C：N ratio （C：NB）, the bacterial growth efficiency （BGE） and ammonium regeneration was mainly examined. The C：Ns ratios varied from 5：1 （carbon limitation） to 40：1 （nitrogen limitation） with varying combinations of glucose and NO3. The C：NB ratio had positive relationship with the C：Ns ratio （r=0.93, n=8）, whose value was 3.77 when the C：Ns ratio was 5：1 but increased to 6.47 when the C：Ns ratio was 40：1. These results indicate that the C：NB ratio is a potential diagnostic tool for determining the bacterial growth in natural waters controlled by either, carbon or nitrogen. BGE decreased with the declining nitrate concentration and negatively related to C：N8 （r=-0.51, n=8）. The average value of BGE was 0.20. This value was a little lower than other reports, which could be induced by the nitrogen source used in our experiments. Finally, regeneration time of ammonium delayed with the increasing C：Ns ratio, which indicates that there were different metabolism mechanisms when bacterial growth was limited by carbon source and nitrogen source.

Exploring the Degradation Potential of Halomonas Bacteria from Oil-contaminated Marine Environment

The degradation potential of a diesel-degrading bacteria(HDMP1) isolated from the oil-contaminated marine environment was explored systematically by analyzing the environmental conditions and synergistic action with other dieseldegrading bacteria. The result indicated that HDMP1 was confirmed as a strain of Halomonas by the method of strain identification. And, HDMP1 showed good diesel degradation performance with a diesel degradation rate of up to 79.59%after 7 days. By analyzing the effect of environmental conditions on HDMP1, the best carbon and nitrogen sources were found to be lactose and peptone, respectively, at a pH value of 7.5 and a salinity of 4 g/(100 mL). Additionally, the synergistic effect of HDMP1 combined with other diesel-degrading bacteria was analyzed by orthogonal experimental design. The inocula of HDMP1, HDMP2, HDMP3 and HDMB3 were optimized, with the best results equating to 0.4%, 0.1%, 0.4% and0.9% in 100 mL of MSM, respectively, while the degradation rate of diesel was identified to be 73.5% within 5 days in the presence of optimum inocula.

Phylogenetic analysis and biological characteristic tests of marine bacteria isolated from Southern Ocean(Indian sector)water

Fifty-seven bacteria were isolated from Southern Ocean （Indian sector） water samples which were collected from different latitude and longitude of the ocean. All the isolates were able to grow at 4℃, 20℃, 37℃ and tolerable NaCI concentration up to 13.5% （w/v）. 29 out of 57 isolates were identified using 16S rDNA amplification and the sequences were submitted to National Center for Biotechnology Information （NCBI）. All the isolates were classified by using Ribosomal Database Project （RDP） and found that isolates belongs to Proteobacteria and Bacteriodes. The average G＋C content was 56.4%. The isolates were screened for the presence of extracellular enzymes, viz. amylase, catalase, urease, esterase, lipase and protease. The disc diffusion method is used to screen antibiotic production by the isolates against four pathogenic bacteria, viz. Salmonella typhimurium （NCIM 2501）, Staphylococcus aureus （NCIM 2122）, Bacillus subtilis （NCIM 2193）, and Pseudomonas aeruginosa （NCIM 2036）. Nine out of 29 were found to be antibiotic producer.

Exopolysaccharides from Marine Bacteria

Microbial polysaccharides represent a class of important products of growing interest for many sectors of indus- try. In recent years, there has been a growing interest in isolating new exopolysaccharides (EPSs)-producing bacteria from marine environments, particularly from various extreme marine environments. Many new marine microbial EPSs with novel chemical compositions, properties and structures have been found to have potential applications in fields such as adhesives, textiles, Pharmaceuticals and medicine for anti-cancer, food additives, oil recovery and metal removal in mining and indus- trial waste treatments, etc This paper gives a brief summary of the information about the EPSs produced by marine bacteria, including their chemical compositions, properties and structures, together with their potential applications in industry.

Heavy-Metal Tolerance and Antibiotic Susceptibility of Red Pigmented Bacteria Isolated from Marine Environment

This study was undertaken to determine heavy metal resistance and antibiotic susceptibility of three non-pathogenic red pigmented bacteria namely WPRA3, SM11-3j and SC-G18, isolated from marine environments of Malaysia. The bacteria isolates were identified by 16S rRNA sequencing and by biochemical and morphological tests. The 16S rRNA gene sequences of all isolates showed ≥96% similarity to Serratia spp. Antibiotic susceptibility test of isolates was assayed according to the Kirby-Bauer disc diffusion method. All isolates were highly resistant to beta-lactam antibiotics, but were susceptible to quinolone antibiotics. Minimum inhibitory concentration (MIC) of nine heavy metals (Ni2+, Co2+, Cr3+, Zn2+, Mn2+, Pb2+, Hg2+, Cd2+ and Cu2+) against the bacteria isolates were determined via the plate-dilution method. The isolates exhibited resistance to Ni2+, Co2+, Cr3+ and Zn2+. Isolates WPRA3 and SM11-3j showed higher multiple tolerances to heavy metals. The results obtained indicate that bacteria from marine environments of Malaysia present interesting metabolic activities, which should be studied and explored for potential biotechnological applications.

Antifouling Potential of Bacteria Isolated from a Marine Biofilm

Marine microorganisms are a new source of natural antifouling compounds. In this study, two bacterial strains, Kytococcus sedentarius QDG-B506 and Bacillus cereus QDG-B509, were isolated from a marine biofilm and identified. The bacteria fermentation broth could exert inhibitory effects on the growth of Skeletonema costatum and barnacle larvae. A procedure was employed to extract and identify the antifouling compounds. Firstly, a toxicity test was conducted by graduated pH and liquid-liquid extraction to determine the optimal extraction conditions. The best extraction conditions were found to be pH 2 and 100% petroleum ether. The EC50 value of the crude extract of K. sedentarius against the test microalgae was 236.7 ± 14.08 μg mL-1, and that of B. cereus was 290.6 ± 27.11 μg mL-1. Secondly, HLB SPE columns were used to purify the two crude extracts. After purification, the antifouling activities of the two extracts significantly increased: the EC50 of the K. sedentarius extract against the test microalgae was 86.4 ± 3.71 μg mL-1, and that of B. cereus was 92.6 ± 1.47 μg mL-1. These results suggest that the metabolites produced by the two bacterial strains are with high antifouling activities and they should be fatty acid compounds. Lastly, GC-MS was used for the structural elucidation of the compounds. The results show that the antifouling compounds produced by the two bacterial strains are myristic, palmitic and octadecanoic acids.

Methods Used to Study Bacterial Diversity in the Marine Environment around Qingdao

Pollution has a considerable effect on biological communities, in terms of size and diversity of the populations. Yet, the precise consequences of human activity on microbial communities in the marine environment are poorly understood. Therefore, in an ongoing collaborative research programme between Heriot-Watt University and the Ocean University of Qingdao, bacteria were isolated in 1999 and 2000 from marine sediment, seawater, seaweed, fish and shellfish, taken from locations in Shandong Province adjacent to Qingdao. Sampling locations were comprised of industrial and aquacultural sites and a clean, control site. In order to analyse microbial diversity, a polyphasic approach was adopted for characterisation of these isolates, specifically through examination of key phenotypic traits, i.e. using Biolog GN MicroPlate TM profiles, bacterial whole cell protein profiles and 16S and 23S rRNA gene sequences. These techniques yielded complex taxonomic data, which were subjected to statistical and cluster analyses. The application of these methods to studies of microbial communities is discussed.

Heterotrophic Bacterial Floras in Industrial Area and Unpolluted Marine Environments around Qingdao

From Oct. 1999 to Oct. 2000, the heterotrophic bacterial floras in the industrial marine environment around the Qingdao Power Plant (QPP) and in the unpolluted marine environments were investigated. The results showed that the numbers of the heterotrophic bacteria around QPP were much higher than those in unpolluted environments, and the average numbers in QPP Seawater, QPP Sediment, Unpolluted Seawater and Unpolluted Sediment were 5.4×104cfu(mL) -1, 5.0×105cfug -1, 3.0×102cfu(mL) -1 and 1.3×105cfug -1 respectively. Totally, 118 strains were isolated from QPP and 99 of them were Gram-negative. One hundred and twenty one strains were isolated from the unpolluted environments and 104 of them were Gram-negative. All the Gram-negative bacteria belonged to 13 genera. The distribution of the bacteria was varied in different marine environments. The results showed that the unpolluted marine environments contained much more Vibrio than seawater and sediment around QPP.

Characterisation of the Bacteria and Archaea Community Associated with Wild Oysters, At Three Possible Restoration Sites in the North Sea

With 85% of the global oyster reefs destroyed, there is an urgent need for large scale restoration to benefit from the ecosystem services provided by biogenic oyster reefs and their associated biodiversity, including microorganisms that drive marine biogeochemical cycles. This experiment established a baseline for the monitoring of the bacterial and archaeal community associated with wild oysters, using samples from their immediate environment of the Voordelta, with cohabiting Crassostrea gigas and Ostrea edulis, Duikplaats with only C. gigas attached to rocks, and the Dansk Skaldyrcentre, with no onsite oysters. The microbial profiling was carried out through DNA analysis of samples collected from the surfaces of oyster shells and their substrate, the sediment and seawater. Following 16S rRNA amplicon sequencing and bioinformatics, alpha indices implied high species abundance and diversity in sediment but low abundance in seawater. As expected, Proteobacteria, Bacteroidetes, Firmicutes and Thaumarchaeota dominated the top 20 OTUs. In the Voordelta, OTUs related to Colwellia, Shewanella and Psychrobium differentiated the oysters collected from a reef with those attached to rocks. Duikplaats were distinct for sulfur-oxidizers Sulfurimonas and sulfate-reducers from the Sva 0081 sediment group. Archaea were found mainly in sediments and the oyster associated microbiome, with greater abundance at the reef site, consisting mostly of Thaumarchaeota from the family Nitrosopumilaceae. The oyster free site displayed archaea in sediments only, and algal bloom indicator microorganisms from the Rhodobacteraceae, Flavobacteriaceae family and genus [Polaribacter] huanghezhanensis, in addition to the ascidian symbiotic partner, Synechococcus. This study suggests site specific microbiome shifts, influenced by the presence of oysters and the type of substrate.

Antibacterial activity of marine bacteria isolated from sponge Xestospongia testudinaria from Sorong,Papua

Objective:To explore secondary metabolite of bacteria-associated Xestospongia testudinaria from Tanjung Kasuari,Sorong,Papua.Methods:The antimicrobial activities of extracts against two Gram-positive bacteria(Staphylococcus aureus) and three Gram-negative bacteria(Pseudomonas aeruginosa,Eschericia coli and Salmonella typhi) were determined by disk diffusion dilution method.Results:The test showed that of 15 isolates of symbiont bacteria,6 isolates were successfully isolated and coded,namely,Xp 4.1,Xp 4.2,Xp 4.3,Xp 4.4,Xp 4.5 and Xp 4.6.Of the six bacterial isolates,isolated Xp 4.2 was found to have more powerful antibacterial activity than any other isolates of symbiont bacteria.Antibacterial activity assay for the n-hexane soluble fractions,ethyl-acetate soluble fractions,and n-buthanol soluble fractions revealed more powerful anti-bacterial activity than any other soluble fractions.Phytochemical screening showed alkaloid and steroid/triterpenoid,while identification for isolate of Xp 4.2 bacterial showed bacteria.Conclusions:Metabolites of bacterial associated with marine sponge Xestospongia testudinaria promise to be developed into antibacterial agents.

Design of Copper Oxide Nanosheets-Loaded Zeolite with Efficient Inhibition of Marine Bacteria

Copper oxide-loaded zeolite 4A nanocomposites(CuO-zeolite NCs)were successfully prepared by modifying zeolite 4A with CuSO_(4)aqueous solution as the copper source.Zeolite 4A showed an important role in hosting copper oxide,and CuO-zeolite NCs exhibited a controlled release of copper ions.XRD patterns confirmed the appearance of new diffraction peaks of copper oxide at 35.83°and 38.83°.CuO nanosheets formed on the surface of zeolite 4A were about 30–40 nm thick over a width of 200–300 nm.CuO-zeolite NCs were primarily composed of Cu,Si,Al and O,as measured by XPS.Cu 2p_(3/2) and Cu 2p_(1/2) peaks were fitted into two main peaks centered at 934.7 eV and 954.6 eV,which were attributed to Cu(II).Zeolite 4A and CuO-zeolite NC displayed reversible Langmuir isotherm(type-I)characteristics and showed maximum adsorption quantities of almost 200 cm^(3) g^(−1) at a relative pressure of 1.0 by CO_(2)adsorption-desorption experiments.The antibacterial efficiencies of the CuO-zeolite NC were 99.4%,96.7%,and 96.8%against Pseudoalteromonas tetraodonis(P.tetraodonis),Micrococcus luteus(M.luteus),and Shewanella putrefaciens(S.putrefaciens),respectively.These values showed that nano CuO-loaded zeolite 4A acted as a strong bactericide against marine bacteria.CuO-zeolite NCs can be further applied to marine antifouling coating.

Preparation of Chiral Hydroxy Esters Using Actinobacteria: Biocatalyst Activity of Marine-Derived <i>Micromonospora</i>and <i>Streptomyces</i>Strains

To research the potential ability of marine-derived actinomycetes to act as biocatalysts, 8 Micromonospora strains and 5 Streptomyces strains were screened. Two recommended media (227 and 1076 media) and 2 modified media (1076-25% and P-1076-25% media) for liquid culture of these marine-derived actinomycetes were tested. As a result, 2 Micromonospora strains (Micromonospora sp. NBRC107096 and 107097) cultured with the 1076-25% medium and 2 Streptomyces strains (Streptomyces tateyamensis NBRC105048 and Streptomyces sp. NBRC105896) cultured with P-1076-25% medium showed a good growth. The stereoselective reduction of α-keto esters using these 4 actinomycetes was tested. As a result, it was found that these strains had a reducing activity toward various α-keto esters. The introduction of L-glutamate or sucrose as an additive remarkably increased the conversion ratios in the reduction of substrates by the Micromonospora strain. Furthermore, in the presence of L-alanine, Streptomyces tateyamensis NBRC105048 reduced ethyl pyruvate, ethyl 2-oxobutanoate, ethyl 2-oxopentanoate, ethyl 2-oxohexanoate, and ethyl 3-methyl-2-oxobutyrate to the corresponding α-hydroxy ester with a high conversion ratio and with excellent enantiomeric excess. Thus, we found that these marine-derived actinomycetes have great potential to be used as biocatalysts for stereoselective reduction of carbonyl compounds.

Enrichment culture of marine anaerobic ammonium oxidation(anammox) bacteria

The present study investigates the enrichment of anaerobic ammonium oxidation(anammox)bacteria in the marine environment using sediment samples obtained from the East China Sea and discusses the nitrogen removal efficiency of marine anammox bioreactor.Enrichment of anammox bacteria with simultaneous removal of nitrite and ammonium ions was observed in the Anaerobic Sequencing Batch Reactor under a total nitrogen loading rate of 0.37kg-N m-3day-1.In this study,The nitrogen removal efficiency was up to 80%and the molar-reaction ratio of ammonium,nitrite and nitrate was 1.0:1.22:0.22 which was a little different from a previously reported ratio of 1.0:1.32:0.26 in a freshwater system.

Metabolic relationships between marine red algae and algae‑associated bacteria

Mutualistic interactions between marine phototrophs and associated bacteria are an important strategy for their success-ful survival in the ocean,but little is known about their metabolic relationships.Here,bacterial communities in the algal sphere(AS)and bulk solution(BS)of nine marine red algal cultures were analyzed,and Roseibium and Phycisphaera were identified significantly more abundantly in AS than in BS.The metabolic features of Roseibium RMAR6-6(isolated and genome-sequenced),Phycisphaera MAG 12(obtained by metagenomic sequencing),and a marine red alga,Porphyridium purpureum CCMP1328(from GenBank),were analyzed bioinformatically.RMAR6-6 has the genetic capability to fix nitrogen and produce B vitamins(B1,B2,B5,B6,B9,and B12),bacterioferritin,dimethylsulfoniopropionate(DMSP),and phenylacetate that may enhance algal growth,whereas MAG 12 may have a limited metabolic capability,not producing vitamins B9 and B12,DMSP,phenylacetate,and siderophores,but with the ability to produce bacitracin,possibly modulating algal microbiome.P.purpureum CCMP1328 lacks the genetic capability to fix nitrogen and produce vitamin B12,DMSP,phenylacetate,and siderophore.It was shown that the nitrogen-fixing ability of RMAR6-6 promoted the growth of P.pur-pureum,and DMSP reduced the oxidative stress of P.purpureum.The metabolic interactions between strain RMAR6-6 and P.purpureum CCMP1328 were also investigated by the transcriptomic analyses of their monoculture and co-culture.Taken together,potential metabolic relationships between Roseibium and P.purpureum were proposed.This study provides a bet-ter understanding of the metabolic relationships between marine algae and algae-associated bacteria for successful growth.

Identification of a marine agarolytic bacterium Agarivorans albus QM38 and cloning and sequencing its beta-agarase genes

A total of 117 agar-decomposing cultures were isolated from coastal seawater around Qingdao, China. The phenotypic and agarolytic features of an agarolytic isolate, QM38, were investigated. The strain was gram negative, strictly aerobic, curved rod and polar flagellum. On the basis of several phenotypic characters, biochemical and morphological characters and phylogenetic analysis of the gene coding for the 16S rRNA, the strain was identified as Agarivorans albus strain QM38. This strain can liquefy the agar on the solid agar plate. An excellular agarase activity was determined in liquid culture. The enzyme exhibited maximal activity at 40 ℃, pH 7.6. Its activity was greatly affected by different concentrations of agarose. The highest activity 32 U/ml was achieved in the culture supernatant. The hydrolytic product was analyzed by fluorophore-assisted carbohydrate electrophoresis （FACE）. After complete hydrolysis of agarose, a series of agaro-oligosaccharides were produced. The main products of the enzymes were oligosaccharides in the degree of polymerization （DP） of 2, 4, 6 and 8. Three genes agaD01, agaD02 and agaD03, encodingβ-agarases, had been cloned from genomic DNA of Agarivorans albus strain QM38. The open reading frame of agaDOl, consisted of 2 988 bp, and shared 95.5%-98.9% identity to the β-agarase genes of some strains of Vibrio and Agarivorans. Gene agaD02 comprised 2 868 bp and encoded a 955- amino-acid protein. It showed 97.4% and 98.7~0 identity to the β-agarase genes of strain Vibrio sp. PO-303 and strain Vibrio sp. JT0107, respectively. Only partial sequence of agaD03 gene has been cloned. It showed 96.5% identity to β-agarase gene （agaB） of Pseudoalteromonas sp. CY24, and shared 96.8% identity to β-agarase-c gene of Vibrio sp. PO-303.

Biological characteristics of marine bacterium S-9801 strain and its culture conditions of pigment production

Strain of Flavobacterium sp.(S-9801),was screened from 207 strains of marine bacteria isolated from the Bohai Sea continental shelf and the Zhujiang Estuary,for its red pigment production.The biological characteristics of strain S-9801 and culture conditions of pigment production have been checked out in this study. The color of the bacterial colony on 2216E medium was from coccineus to rose bengal. Optimum culture conditions were sodium chloride concentration(g/dm3),10～30;pH,3～8;temperature,25～28℃;tryptone and yeast extract as nitrogen sources and glucose as carbon source. Under optimum conditions,pigment accumulation started after 12 h,reaching a maximum rate of synthesis at 36 h.

Distinct influence of trimethylamine N-oxide and high hydrostatic pressure on community structure and culturable deep-sea bacteria

Trimethylamine N-oxide(TMAO)is one of the most important nutrients for bacteria in the deep-sea environment and is capable of improving pressure tolerance of certain bacterial strains.To assess the impact of TMAO on marine microorganisms,especially those dwelling in the deep-sea environment,we analyzed the bacterial community structure of deep-sea sediments after incubated under different conditions.Enrichments at 50 MPa and 0.1 MPa revealed that TMAO imposed a greater influence on bacterial diversity and community composition at atmospheric pressure condition than that under high hydrostatic pressure(HHP).We found that pressure was the primary factor that determines the bacterial community.Meanwhile,in total,238 bacterial strains were isolated from the enrichments,including 112 strains a ffiliated to 16 genera of 4 phyla from the Yap Trench and 126 strains a ffiliated to 11 genera of 2 phyla from the Mariana Trench.Treatment of HHP reduced both abundance and diversity of isolates,while the presence of TMAO mainly af fected the diversity of isolates obtained.In addition,certain genera were isolated only when TMAO was supplemented.Taken together,we demonstrated that pressure primarily defines the bacterial community and culturable bacterial isolates.Furthermore,we showed for the first time that TMAO had distinct influences on bacterial community depending on the pressure condition.The results enriched the understanding of the significance of TMAO in bacterial adaptation to the deep-sea environment.