Studies On Microbial Biodiversity Of Toxic Alexandrium Catenella And Their Potential Algae-bacterial Interactions

The aquatic ecological problems caused by harmful algal blooms(HABs)have occurred widely,which not only greatly hindered the development of coastal economy and polluted drinking water resources,but also endangered human health and safety through bioaccumulation,and even led to death.Among them,paralytic shellfish poisoning(PSP)has the strongest toxicity,the widest distribution and the greatest harm among the toxins produced by harmful algal blooms.However,the source of PSP is still an unsolved mystery.The relationship between algae and bacteria is an important breakthrough to reveal the source of PSP,and the first prerequisite is to analyze the structure and function of microbial flora producing PSP dinoflagellate.In this study,the second-generation sequencing(16S r RNA V3-V4 variable region gene)and the third-generation sequencing(16S r RNA full-length gene)were used to study the bacterial diversity of the representative PSP-producing dinoflagellate,Alexandrium catenella ALC,and to analyze the structural characteristic microbial community of the toxic Alexandrium catenella ALC.PICRUST1.1.0 software was used to predict the function of its bacterial community,so as to have a preliminary understanding of the function of its microflora.The results were as follows: 7 phyla,15 classes,35 orders,54 families and 82 genera were identified by second-generation sequencing.The proportions of unknown genera and new species were 12.65% and 92.89%,respectively.There were 2 phyla,3classes,8 orders,9 families and 13 genera in the sequencing annotation of the third generation.The unknown genera accounted for only 1.05%,but the proportion of new species was as high as 99.21%.The dominant phylum,class,order,family and genus of the sequencing of the second and third generations were consistent,which were Proteobacteria,Alphaproteobacteria,Rhodobacterales,Rhodobacteraceae,and Marivita,respectively.16 S r RNA function prediction showed that carbohydrate enzymes were mainly glycosyltransferase(GT)and glycoside hydrolase(GH),and polysaccharide lyase(PL)was very little.Comparison between KEGG and COG databases showed that in addition to the basic biological processes,the functions mainly focused on the genes related to amino acid and carbohydrate metabolism.Two strains of bacteria were obtained from the toxigenic Alexandrium catenella ALC by microorganism isolation and pure culture technology.And their genera were identified as Marivita and Maritimibacter by 16 S r RNA sequence alignment.The strain LZ-15-2 was selected for polyphasic taxonomic identification,and it was confirmed that LZ-15-2 was a new member of Marivita cryptomonadis.Based on COG functional annotation,KEGG metabolic pathway annotation and selection of gene clusters for the synthesis of secondary metabolites,the following symbiosis mechanisms between strain LZ-15-2 and toxigenic Alexandrium catenella ALC were speculated from the gene level: 1,vitamin B2 and B6(essential growth factors)can be synthesized;2,detoxification and drug resistance mechanisms exist(degradation of toxic substances and efflux pump of multidrug resistance);3,Providing and exchanging nutrients or participation in their synthesis(metabolism of sulfur and nitrogen,existence of photosynthesis and carbon sequestration);4,Chemical defense(biosynthesis of antibiotics,polyketones and terpenoids);5,Presence of quorum sensing signal molecule(N-acyl homoserine lactone),with information exchange mechanism between algae and bacteria.