Study On Microbial Diversity And Quorum-sensing Bacteria In Mussel Symbiosis In The Indian Ocean Hydrothermal Area

As an extreme environment with large temperature changes,high toxicity,and low oxygen,the deep-sea hydrothermal area is home to a large number of organisms,including the mussel Bathymodiolus marisindicus.Studies have shown that it's stress resistance is related to associated microorganisms,but the diversity and functions of these symbiotic microorganisms are rarely studied.Although there is evidence that there is a Lux S-type quorum sensing system in hydrothermal associated microorganisms,the most known Lux I/R-type quorum sensing system in nature has not been found.Whether this type of quorum sensing system exists in hydrothermal associated microorganisms,and if it exits,how it contributes to the adaptation to extreme environments is unclear.Based on the above scientific problems,we studied the diversity characteristics of associated bacteria in the mussel gills in Tiancheng and Longqi hydrothermal areas of the southwest Indian Ocean,and isolate and identify culturable associated bacteria in mussel gills of Tiancheng hydrothermal area.Quorum-sensing bacteria were screened,and the types of quorum-sensing signal molecules,membrane-forming and DMSP utilization abilities were explored.Finally,a representative quorum-sensing bacterium was selected for whole-genome sequencing in order to analyze the functional genes and metabolic pathways associated with extreme environmental adaptation.The results show:(1)The diversity of associated microorganisms in the gills of hydrothermal mussels and shallow sea mussels shows that,at the phylum level,the dominant categories of associated microorganisms in the gills of hydrothermal and shallow sea mussels are Proteobacteria.At the subordinate level,the gills of hydrothermal mussels contain a large amount of bacteria of group Sup05,which does not exist in the gills of shallow sea mussels.The bacteria of group Sup05 are a group that exists in the deep-sea environment,which can associated with the gills of deep-sea mussels,having the function of sulfur oxidation.They can help the mussels survive in the hydrothermal environment with high H₂S.?-Diversity and?-Diversity showed that there was little difference between associated bacteria in Tiancheng and Longqi hydrothermal mussel's gill,but they were both different from Shallow Sea mussel.Due to the great difference between hydrothermal and shallow sea environment,mussels living in them also had great differences in the types of bacteria they chose to associated with in order to adapt to the environment.(2)96 strains of associated bacteria were isolated from the gills of hydrothermal mussels.According to the 16S rDNA Gene sequence,25 different strains were identified,which belong to 4 phyla,5 classes and 14 genera.Proteobacteria is the dominant flora,accounting for 64%,and Roseobacteria group accounts for 20%.Three strains of quorum sensing bacteria(Sulfitobacter pontiacus TCYB15,Sulfitobacter pontiacus TCYB21 and Roseivivax marinus TCYB24)were screened.They have the ability to produce two AHLs signal molecules called C8-HSL and C6-HSL.They all have the potential to form biofilms and utilize DMSP.This study confirmed the existence of quorum sensing bacteria in the associated microorganisms of hydrothermal mussels,and speculated that they could form biofilms in gills and participate in the sulfur cycle in the process of associated with mussels.(3)The quorum sensing bacterium TCYB15 has a genome size of 3640800 bp,including a total of 1 chromosome,4 circular plasmids and 3536 coding genes.It contains genes related to quorum sensing(luxI/luxR homologous gene),degradation of DMSP(dddL gene),Soxthiooxygenation system(soxX,soxY,soxZ,soxA,soxB,soxC),and ABC heavy metal transport system(afuA,fbpA,afuB,fbpB).