Microbial community structure and its relationship with environmental factors on Hole-Rotten disease of Saccharina japonica in coastal Putian

In order to explore microbial community structure and the correlation between environmental factors and community structure on Hole-Rotten disease of kelp Saccharina japonica in coastal regions of Putian, in this study, 16S rRNA gene amplicon sequencing technology was used to analyze the samples of healthy (HT) S. japonica, S. japonica with Hole-Rotten disease (DT), seawater from area of cultivated healthy S. japonica (HS) and seawater from area of cultivated S. japonica with Hole-Rotten disease (DS). The interactions between seawater microbial and environmental factors were analyzed by redundancy analysis (RDA) as well. The results showed that the Ace index, Shannon index and Heip index were significantly different between HT and DT samples (P<0.05), the Ace index and Shannon indes were significantly different between HS and DS samples (P<0.05), while the Heip index was not significantly different (P>0.05). The results of principal co-ordinate analysis showed that the microbial community of each sample was obviously partitioned. Microbial community composition analysis showed the relative abundance of Halomonadaceae in the HT and DT samples were 1.63% and 49.01%, the relative abundance of Cyanobacteria in the HS and DS samples were 74.45% and 3.89%, respectively. The relative abundance of Pseudoalteromonadaceae in DS samples is 30.87%, nevertheless, less than 1% in HS samples. The results of correlation analysis of environmental factors showed the salinity and temperature were significantly different in the association between HS and DS samples (P<0.05), and the explanations for the variation of seawater microbial communities were 46.75% and 42.42%, respectively. The dominant Cyanobacteria in seawater was positively correlated with salinity and negatively correlated with temperature; the dominant Flavobacteriaceae, Rhodobacteraceae, Pseudoalteromonadaceae and Vibrionaceae, were negatively correlated with salinity and positively correlated with temperature. In summary, the occurrence of Hole-Rotten disease may be intimately related to the Halomonas in S. japonica epiphytes and the Cyanobacteria and Pseudoalteromonadaceae in seawater microorganisms. Salinity and temperature might be the key environmental factors leading to the change of seawater microflora.