Study On The Diversity And Community Structure Of Marine Vibrio In The Beibu Gulf

Marine Vibrio is a kind of heterotrophic Gram-negative bacteria,which is short and facultative anaerobic with halophilic,motility and positive oxidase and widely distributed in estuarine,coastal,sediment,aquaculture areas and marine animals.It is well known that pathogenic Vibrio is closely related to the development of aquaculture and human health.Besides,Vibrio also plays an important role in the element cycle of marine ecosystem.Therefore,the pure culture,classification and identification and community structure diversity of marine Vibrio have always been one of the hot topics on microbial ecology.Beibu Gulf is a natural semi-enclosed bay and traditional fishing ground in the northwest of the South China Sea,with rich in biodiversity.Recently,due to the impact of runoff input and human activities,its eutrophication is not optimistic,resulting in frequent outbreaks of marine Vibriorelated disasters.In this study,we isolated the Vibrio by Thiosulfatecitrate-bile salts-sucrose(TCBS)agar medium from the whole Beibu Gulf.The Vibrio species was identified by 16 S rRNA and related functional genes.The high-throughput sequencing technology and bioinformatics methods were used to analyze the diversity of marine Vibrio community,seasonal variation of Vibrio and its key environmental control factors.The main results are as follows:1.We isolated 1,037 strains of Vibrio from 45 seawater and biological samples from Maowei Sea,Qinzhou Bay and Beibu Gulf open sea,and identified 18 different Vibrio species and potential species(16S r DNA gene similarity below 90%).Vibrio alginolyticus,V.cyclitrophicus,V.tasmaniensis,V.brasiliensis,and V.splendidus were the dominant species(>10%).The results showed that culturable Vibrio had regional distribution characteristics.Salinity,nitrogen,and phosphorus were the main factors affecting the diversity of culturable Vibrio.2.A total of 20 strains of V.parahaemolyticus that came from seawater and aquatic animals in Maowei Sea aquaculture area were identified by DNA sequencing of 16 S rRNA genes and specific function gene toxin regulations(tox R)after PCR amplification,with a detection rate of 18.3%.Virulence gene tdh analysis showed that 4 of the 20 strains of V.parahaemolyticus carried the virulence gene thermostable direct hemolysin(tdh),with a detection rate of 20%.In addition,phylogenetic analysis also revealed horizontal gene transfer happened in both the tox R and tdh gene sequences of V.parahaemolyticus.3.Shannon diversity of the Vibrio community that came from Maowei Sea seasonal water samples was highest in summer,while ?-diversity analysis showed that Vibrio community structures were significantly different between seasons.Distance-based redundancy analysis(db RDA)and Mantel test analysis suggested that total dissolved nitrogen(TDN),total dissolved phosphorus(TDP),dissolved inorganic nitrogen(DIN),salinity,and temperature were the key environmental factors shaping Vibrio community structure,indicating a strong environmental filtering effect of trophic condition on the Vibrio communities.Furthermore,through random forest analysis,V.fluvialis,V.alginolyticus,V.proteolyticus,V.splendidus and the other eight Vibrio species were more sensitive to the eutrophic changes.In summary,this study fills the gap on the Vibrio diversity in Beibu Gulf,and provides data theoretical support for preventing the outbreak of pathogenic Vibrio and analyzing the ecological function of Vibrio.