Analysis Of Epiphytic Bacterial Diversity Of Cultured Saccharina Japonica At Different Growth Stages

Saccharina japonica is a kind of economic kelp that has been cultivated on a large scale in China.The bacteria attached to its surface play an important role in the growth and development of S.japonica.In this study,kelp cultured artificially in Rongcheng was taken as the research object.The kelp,the seawater of aquaculture area and the seawater outside the aquaculture area were collected at different stages of aquaculture.The 16S rRNA gene amplicon sequencing technology was used to study the diversity and dynamic changes of the bacterial community structure on the surface of kelp and the seawater body.The culturable groups were isolated and cultured from the samples of the lowest and highest bacterial community diversity.It was found that the structure of bacterial community on the surface of S.japonica was significantly different from that in seawater.Bacterial communities on the surface of S.japonica were Proteobacteria,Bacteroidetes,Verrucomicrobia and Planctomycetes.At the same time,the bacterial community composition on the surface of S.japonica showed the difference in time distribution.The bacterial community composition was in the process of dynamic change.The bacterial community structure on the surface of kelp was significantly different in different culture periods,and each culture period had unique dominant bacteria.The diversity and richness of the bacterial community on the surface of the S.japonica in mature stage were the lowest,and the diversity and richness of the bacterial community on the surface of the S.japonica in senescence stage were the highest.Meanwhile,it was found that the bacteria of Persicirhabdus,Granulosicoccus and Loktanella were the core microbiome on the surface of kelp and they had a certain abundance in each period sampled of culture.The abundance and diversity of bacterial communities in seawater are higher than those on the surface of S.japonica.The bacterial communities in seawater mainly include the following groups,Proteobacteria,Bacteroidetes,Campilobacterota,Dadabacteria,Marinimicrobia_SAR406 Clade,Verrucomicrobia,Chloroflexi,Firmicutes,SAR324 cladeMarine_group_B,Cyanobacteria,and Nitrospinota.The bacterial community composition of seawater showed temporal and spatial distribution differences.On the one hand,the composition of the bacterial community in seawater was significantly different at different periods of culture.On the other hand,S.japonica culture has a certain influence on the composition of bacterial community in aquaculture seawater.Especially in the thickening and mature stage,the composition of bacterial community in the seawater water body of S.japonica culture area and outside the culture area had a great difference.Nutrient concentration in seawater is significantly correlated with bacterial community composition,bacterial community diversity in seawater is significantly positively correlated with NH4+and NO3-concentrations,and community richness is significantly positively correlated with NO3-,NO2-and PO43-concentrations.When inorganic nitrogen and phosphorus are abundant in seawater,the number and variety of microorganisms are more.With thickening and senescence stage japonica as the strain separation work samples.By improving the isolation and culture method,total separation for 774 strains that distribution in the following six phylum,Proteobacteria,Bacteroideter,Actinobacteriota,Planctomycetes,Firmicutes and Verrucomicrobia.Including 148 novel strains that enriched the algae associated bacteria resource.Comparing the diversity of culturable groups in the two stages of S.japonica,it was found that the number and diversity of culturable groups on the surface of the thickening stage were higher than that of the senescence stage.