Species Diversity And Screening Of Toxin Strains Of Symbiotic Bacteria From Toxic Dinoflagellate Alexandrium Tamarense

Harmful algal bloom(HABs) is a global ecological disasters and major environmental problems. Alexandrium tamarense is one of the typical world-wide red-tides dinoflagellates, which produces paralytic shellfish poison(PSP) toxicin. PSP is known to possing the strongest toxicity, most widespread, most harmful, most frequenency among the known red-tide toxins. In recent years, the marine ecological environment pollution along China coasts become increasingly aggravated, directly leading to frequent red-tides occurrence. It has brought huge threat to marine fisheries, aquaculture and aquatic products quality and safety, and can cause human poisoning and death through the food chain transfer.Therefore, applied basic research on harmful algal bloom will realize its scientific prevention & control. But the issue of the ture PSP source has remained unsolved yet. Bacteria and algae interaction is the key to reveal PSP production mechanism. The toxic dinoflagellates have huge genome(3-245 Gbp, 1-80 times of the human genome), is still difficult to effectively carry out the whole genome sequencing analysis, which causes the research progress on the PSP producing mechanism isat relativeslowerrate. Compared with the host algae, symbiotic bacteria has smaller genome size, easy to cultivate, simpler to genetic operation.So, performingits PSP synthesis mechanism studycan gain breakthrough in a simpler & easier way compared with its host dinoflagellates.In this study, the toxic dinoflagellate, Alexandrium tamarense(880#),was chosen as the research material, the high-throughput sequencing analysis of the symbiotic bacteria was performed by species and abundance of species. its symbiotic bacteria strains were isolated through microbial pure culture method.The potential new species was identified by polyphasic taxonomy analysis. Through genetic testing and chemical analysis, the toxic symbiotic bacteria were screened. Results showed thattotal 87 matching data were obtained with 5% unknown spicies. Its biodiversity includes 57 genera and five dominant genus including Rhodobacteraceae sp., Marinobacter sp., Methylophaga sp.,Nitratireductor sp and Phycisphaera sp.. In addition, 11 cultivated bacterial strains were isolated by microbial pure culture method, belonging to 6genuses including Nitratireductor sp., Roseibacterium sp., Paracoccus sp.,seabacillus sp., Amorphus sp., Arthrobacter sp.. Two bacteria strains are potential new species with their 16 S rRNA gene sequence homology are97.0% and 97.64%, respectively. The optimization of PSP genetic analysis for the toxin bacteria strains was performed and 11 cultivated strains werescreened. The results showed that 4 positive strains were found. Meanwhile,LC-MS analysis of PSP toxins for the fermentation metabolites was detected. As a result, this study can provide a scientific reference strategy for the optimization of cultivated symbiotic bacteria in toxic dinoflagellates,and it can provide important support of materials and biological background information for subsequent research on algae-bacteria interaction research.