Species Diversity And Bacteria Influence On The Production Of Paralytic Shellfish Toxins By Toxin Dinoflagellate Alexandrium Catenella

Harmful algal blooms?HABs?is a serious marine ecological disaster globally and a major hot environmental issue.Marine red-tide toxins arise from HABs cause great harm to the health of the human beings.Among the diverse red-tide toxins,paralytic shellfish poison?PSP?is most widespread and have strong toxicity.However,the issue of the real source of PSP remains unsolved.Algae-bacterial interaction?ABI?is the key to reveal PSP production mechanism.Moreover,the study of the biodiversity of the bacterial community associated with toxin dinoflagellate is a necessary prerequisite for the furthering ABI study.In this study,to reveal the biodiversity of the bacterial community associated with a typical toxic red-tide dinoflagellate,Alexandrium catenella?LZT09?,the species types and their relative abundance were analyzed using high-throughput sequencing.The result showed that the bacterial community belong to 6 phylums,which the three dominant were proteobacteria?53.95%?,Bacteroidetes?27.52%?and Cyanobacteria?16.81%?.Furthermore,these 6 phylums were classified to 34 genus,while the dominant includes unknown species in family Cryomorphaceae?22.86%?,unknown species in Cyanobacteria?16.81%?,Saccharospirillum sp.?14.65%?,unknown species in family Rhodobacteraceae?7.93%?and Maricaulis sp.?5.64%?.The total proportion of unknown species is about 50.6%,indicating that Alexandrium catenella?LZT09?has great potential to discover new species.Pure culture was also carried out and 12 cultivable bacterial strains were obtained,among which the strain LZ-16-1 can produce dcneoSTX toxin.The polyphasic taxonomy analysis was performed on the possible novel species,strain LZ-7.The results showed that strain LZ-7 is a Gram-negative,coccoid to short rod-shaped,strictly aerobic bacterium.The strain grew optimally in the presence of 6%sea salts,at a temperature of 28?and at pH 7.The polar lipid profile of strain LZ-7 comprised phosphatidylglycerol,phosphatidylethanolamine,phosphatidylcholine.The major fatty acids were C_18:1?7c?65.33%?C_16:0?9.27%?,C_18:0?7.56%?,C_18:1?7c11-metyl?5.6%?,C_17:0?3.83%?,C_12:0-3OH?3.75%?,C_12:1-3OH?2.20%?.Ubiquinone10 was the major quinone.The DNA G+C content was 68.2 mol%.Strain LZ-7 exhibited highest 16S rRNA gene sequence similarity to Ponticoccus litoralis CL-GR66^T?98.37%?.Therefore,strain LZ-7 is identified as a novel species of Ponticoccus,the proposed name is Ponticoccus sp.LZ-7.The result obtained by ABI study showed that the pretreatment of Alexandrium catenella?LZT09?with 30?g/mL of cefotaxime sodium and 50?g/mL vancomycin removed most of the epipsymbiotic bacteria of the host dinoflagellate.The PSP toxins profile in both the culture treated by the antibiotics and the control group remained the same,except for that the PSP yield of the treatment group was about 78%lower than that of the original group.