Diversity Of Porites.Associated Bacteria And Its Pure Culture Study

Coral reef ecosystem is one of the most productive ecosystems in the world.It provides food and income for millions of people along the coast with less than1%of the area covered.However,current research shows that global living coral coverage is being drastically reduced due to the impact of human activities and natural environment changes,such as overfishing,large-scale mechanical damage,global warming caused by excessive CO₂ emissions,and coral bone erosion caused by ocean acidification.A large number of studies at home and abroad have pointed out that when corals are under environmental pressure,the composition of coral associated bacterial community will change,which may be related to the health maintenance and recovery of corals.The study of coral associated bacteria will help us to understand the relationship between bacteria and coral health,understand the intrinsic mechanism of coral degradation,and create conditions for coral reef recovery.However,the study of coral associated bacteria started late and needs to be further explored.At present,massive coral represented by Porites replace branched coral as the dominant species in multiple Marine areas.It proves that massive coral have stronger adaptability and anti-interference ability to the current environment.Therefore,Porites lutea and Porites lobata were selected as research objects in this paper to analyze the diversity of coral associated bacteria and to conduct pure culture research on coral associated bacteria.Firstly,the diversity of Porites associated bacteria was studied by using High-Throughput sequencing technology.High-Throughput sequencing results of V3-V4 high variation region of 16S rRNA gene showed that the main bacterial groups of the two Porites and the highest proportion are Proteobacteria,86.11%,Bacteroidetes,23.13%,Cyanobacteria,16.05%,Actinobacteria,4.87%,Firmicutes,2.4%and so on.At the same time,the study showed that the host species and the growing environment of corals had a significant impact on the community structure of coral associated bacteria.In addition,the data indicate that a large number of suspected pathogens Vibrio sp.and probiotics Pseudoalteromonas sp.,Ruegeria sp.coexist in healthy corals.Secondly,the pure culture research was used to cultivate the coral associated bacteria of cultured Porites.sp sampled in Weizhou island.A total of 302 strains were obtained from oligotrophic culture,among which 123 strains were obtained from marine agar 2216E medium,66 strains were obtained from seawater GYP agar medium,113 strains were obtained from seawater R2A agar medium.After the preliminary identification of 16S rRNA gene,these strains were divided into6 phylum,Proteobacteria,Bacteroidetes,Actinobacteria,Acidobacteria,Firmicutes,respectively.11 class,18 order,30 family,63 genus.18 suspected new species have been identified.The culturable bacteria were concentrated in?-proteobacteria,Bacteroidetes and Flavobacteria,however,The result obtained by High-Throughput sequencing were mainly concentrated in?-Proteobacteria and Bacteroidetes.In addition,the High-Throughput sequencing technology found a large number of Ralstonia,but can't be pure culture.Thirdly,4 potential new species were identified by polyphasic classification.It turned out that the 4 potential new strains represented 3 new genera and 4 new species,namely,Sulfidibacter coralliicola gen.nov.,sp.nov.,Poritesiphilus weizhouensis gen.nov.,sp.nov.,Prasibacter corallicola gen.nov.,sp.nov.,Aliikangiella coralliicola sp.nov..Among them,the H₂S production of sulfide producing bacteria in corals is controlled by nutritional conditions,and eutrophication will lead to the production of a large number of H₂S,which may cause damage to the coral reef ecosystem.Finally,through culture-independent and culture-dependent methods,this study found that suspected pathogens and probiotics coexist in healthy corals,and changes in environmental conditions may affect the health of corals by changing the bacterial community structure through microbial metabolism.However,this study has only uncovered the tip of the iceberg of coral associated bacteria,and the functions of coral associated bacteria such as Ralstonia sp.,which are restricted by pure culture,need to be further studied.