Conchocelis Microflora And Environmental Factors Of Seedling Pools Associated With Yellow-spot Disease Of Pyropia Yezoensis

Pyropia is an important marine crop.It has a more than 20 billion per year yield scale all over the world which accounts for 60 percent of the whole seaweed industry.China is a major Pyropia producing country,in which more than 60000 tons?dry weight?were annually produced.P.yezoensis is the most economically valuable species of Pyropia due to its high quality and added value.However,with rapid expansion of the industrial cultivation,disease problems are increasingly obvious.Yellow spot disease of shell-boring conchocelis of Pyropia yezoensis usually causes enormous losses to aquaculture Industry.However,little is known about microbiota of conchocelis under health status and of its transformation after disease.In this study,bacterial composition and variation were compared between healthy and diseased conchocelis by using next-generation sequencing and 16S rRNA gene sequences.A total of 1.6 Gb paired-end reads were generated,which is also the first high-throughput dataset for microbial communities of shell-boring conchocelis.Totally 7,833 unique OTUs and 18 bacterial phyla were identified.Compared with the healthy samples,microbial diversities of the diseased samples increased significantly.Both PCoA and UPGMA tree divided these samples into two distinct groups.Distance within health group was remarkably smaller than within disease group,indicating the similar community composition between samples of the former.Significant difference between two groups was shown in 39 genera,29 of which were more abundant in healthy samples.Our study detected microbiota of shell-boring conchocelis at community-wide,and will provide valuable information for detection and prevention of yellow spot disease.Shell conchocelis cultivation is a crucial step in the industrial growth of Pyropia.However,our knowledge of the seawater microbiology community in Pyropia seedling pools is limited.This study investigated the temporal changes in seedling pool microbiota during outbreaks of yellow spot disease in Pyropia yezoensis conconcelis.A total of 18 water samples were collected to assess seedling pool health status,followed by the sequencing of microbiota 16S rRNA.Analysis of 16,760,224 16S rRNA gene sequences indicated that the core microbe group comprised 207 genera.The microbial diversity of samples gradually increased from May to July.The bacterial diversity of seawater samples from diseased P.yezoensis seedling pools was significantly higher than samples from healthy seedling pools,and each pool group had a distinctive microbial community composition.The relative abundance of two dominant bacteria genera,Sediminicola and Roseivirga,increased over time in healthy seedling pools,peaking in August,while Vibrio remained at constantly low levels.However,the abundance of Vibrio and Polaribacter increased sharply in diseased P.yezoensis seedling pools,and decreased after fresh seawater exchange.This indicates that these bacteria are probably associated with the filament disease.Many disease associated bacteria are negatively related to the HCO₃^-concentration in seawater and positively related to pH.Changes in bacteria and environmental factors reflect the characteristics of microbial community succession in seedling pools,and can therefore be used as biomarkers and environmental signals for Pyropia disease monitoring.