Diversity Of Culturable Bacteria From The Mariana Trench And Their Ability To Degrade Macromolecules

The Mariana Trench,located in the Western Pacific Ocean,represents the deepest location on the earth at the depth of almost 11000 m.Due to the unique deep-sea geographic feature,such as high pressure,low temperature,low oxygen content,darkness,and lack of nutrients,microbes here likely have a specific community composition and unique metabolic characteristics.Thus,the Mariana Trench microbial community has become a hot area due to its crucial role in global biogeochemical cycle and its exploitable merit.This thesis,took the different water layers and sediment samples of the Mariana Trench as the research materials,explored the diversity of culturable bacteria in the Mariana Trench and the degradation ability of macromolecular substrates of the isolated culturable bacteria.Moreover,a novel bacterium isolated from the Mariana Trench was further taxonomically characterized using the polyphasic approaches and,based on the results,it is proposed to represent a novel genus and species within the family Alteromonadaceae.1.Diversity of culturable bacteria in different water layers and sediments of the Mariana TrenchBacterial strains,isolated from different water layer and sediment samples obtained from various operating sites of the Mariana Trench voyage in March 2019,were purified by the dilution-plate method and the streaked plate method.The classification statues of 317 culturable bacteria was determined according to their 16S rRNA gene sequences.Among the 317 strains,248 were isolated from seawater samples and 69 were isolated from sediment samples.According to the results,these culturable bacteria belong to 4 phyla,6 classes,45 genera,and 78 species.Gammaproteobacteria has the highest relative abundance in the samples,with a total of 214 strains.The dominant genera are Halomonas(80 strains)and Idiomarina(49 strains),which account for 25.2%and 15.5%of the total number of strains,respectively.Among these isolated strains,a total of 23 strains,sharing less than 98.7%16S rRNA gene sequence similarities to known bacteria,may represent new species or genera,accounting for 7.3%of the total number of isolated strains.2.Study on the ability to degrade macromolecules of culturable bacteria in Mariana Trench317 strains of culturable bacteria were investigated for the degradation ability of macromolecules by measuring the H/C ratios(the ratio of the hydrolytic zone diameter to the colony diameter)of colonies on the plates containing different substrates.The results showed that 65.9%of the isolated strains had the ability to degrade macromolecular substrates,and 39.4%of the isolated strains could degrade two or more macromolecular substrates.There were 167 gelatin-degrading bacteria,86 casein-degrading bacteria,81 agar-degrading bacteria,80 carrageenan-degrading bacteria,26 alginate-degrading bacteria,and 4 chitin-degrading bacteria.Further analysis showed that the number of protein-degrading bacteria was higher than that of polysaccharide-degrading bacteria.In addition,71.0%of bacteria from sediment samples had the ability to degrade macromolecular substrates,and 64.5%of bacteria from seawater samples had the same ability.3.Polyphasic taxonomic analysis of strain Marinifaba aquimaris SM1970TA novel Gram-negative,rod-shaped,aerobic,oxidase-positive and catalase-negative bacterium,designated strain SM1970T,was isolated from the seawater sample collected from the Mariana Trench.Strain SM1970T grew at 15-37? and with 1.0-5.0%(w/v)NaCl.It hydrolyzed agar and casein but did not reduce nitrate to nitrite.Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SM1970T formed a distinct lineage close to the genus Catenovulum within the family Alteromonadaceae,sharing the highest sequence similarity(93.6%)with type strain of Catenovulum maritimum but<93.0%sequence similarity with those of other known species in the class Gammaproteobacteria.The major fatty acids of strain SM1970T were summed feature 3(C16:1?7c and/or C16:1?6c),C16:0 and summed feature 8(C18:1?7c and/or C18:1?6c).Strain SM1970T contained phosphatidylethanolamine and phosphatidylglycerol as major polar lipids and its main respiratory quinone was ubiquinone 8.The draft genome of strain SM1970T consisted of 77 scaffolds and was 4172146 bp in length.The average amino acid identity(AAI)values between SM1970T and type strains of known Catenovulum species were 56.6-57.1%while the percentage of conserved proteins(POCP)values between them were 28.5-31.5%.The genomic DNA G+C content of strain SM1970T was 40.1 mol%.Based on all polyphasic data obtained in this study,strain SM1970T is classified into a novel species in a novel genus of the family Alteromonadaceae,for which the name Marinifaba aquimaris is proposed with the type strain being SM1970T(=MCCC 1K04323T=KCTC 72844T).In summary,this study on the diversity of culturable bacteria in Mariana Trench and their ability to degrade macromolecules can not only enhance people's understanding of the diversity and complexity of marine microorganisms,but also deepen the understanding of the circulation of materials in marine ecosystems.Moreover,this study may provide useful information on discovering and developing marine microbial resources.