Biodiversity Study Of Symbiotic Bacterial Community Associated With Toxic Dinoflagellate Alexandrium Minutum(Amtk4)and Phylogenetic Gene Analysis

Harmful algal blooms(HABs)and paralytic shellfish poisoning(PSP)toxins is global ecological disasters and major environmental issue.Alexandrium minutum is a typical global red-tide causing marine dinoflagellate producing PSP toxins and others toxins,it was able to frequently trigger red tides in the East China Sea.Moreover,transmitted through food chain and seriously endangering the seafood safety,once people eated the seafood polluted by PSP that were eriously endangering human life and health.However,the orign of PSP is a controversial issue that was produced by host algae or algal associated bacterial.Therefore,it is essensial to go into the PSP toxins biosynthesis and orign for preventing and controlling PSP.Algae-bacteria interaction has laid a foundation for revealing the role of algal symbionts in the production of PSP and the biosynthesis of PSP.At present,there is no systematic investigated for this issue.The whole genome of the dinoflagellate is too large to gene sequencing,but the algal associated bacterial features are easier to culture and small whole genome.Therefore,it is easier to breakthrough bottleneck in the orign and bilsynthesis of PSP from the perspective of self-produced strains.In this study,the species types and relative abundance of the algal associated bacterial community of Alexandrium minutum amtk-4 were analyzed by high-throughput sequencing.Five cultivable bacterial strains of amtk-4 were also isolated;identitied the strain Z1-D by polyphasic taxonomy methods;analized gene evolution of sxtA1 gene of the novel species strain Z1-D.Based on the results obtained,the algal associated bacterial community of amtk-4 includes 6 gates,14 classes,28 orders,45 families and 64 genera,with 6 dominant genera including Lactococcus(25.5%),Dinoroseobacter(19.8%),Roseovarius(8.6%),Bacillus(6.2%),and Rhodobacteraceae(6.1%).Total 59.7%of the bacteria belonged to novel genus.Two cultivable bacterial strains including Z1-4 and Zl-D were identified as novel species of Sulfitobacter and Mesorhizobium,respectively.The strain Z1-D was identified as a new species of genus Ponticoccus by bacterial polyphasic taxonomy,named Sulfitobacter Alexandri Z1-DT;gene fragment of orf01498 of strain Z1-D with the production ability of saxitoxin(STX)showed high similarity with sxtAl genes from the cyanobacteria,such as Aphanizomenon flos-aquae and Cylindrospermopsis raciborskii.Predicted protein tertiary structure of eight sxtAl highly homologous gene fragments in the strain Zl-D genome conforms to the typical structural features of SAM-methlyl transferase.It is indicated that the new species of strain Z1-D has a genetic basis for PSP initiation synthesis.This study provided strain materials for the orign of PSP and scientific basis for the toxigenic gene analysis of the associated bacteria.