[Microbial diversity of Pyropia haitanensis phycosphere during cultivation]

Pyropia haitanensis is of great commercial importance and wildly cultivated in Zhejiang and Fujian provinces. To observe the characteristics and changes of phycosphere microbial communities during cultivation can help us monitor the potential pathogens and microbial factors affecting the health of cultivated seaweeds.

The morphological characteristics and the diversity of phycosphere and surrounding seawater microbes were studied by pure culture method and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Similarity analysis was carried out online with the 16S rDNA (bacteria) and 18S rDNA (fungi) sequences in GenBank. The phycosphere microbial diversity during different growth stages, cultivated areas and periods was studied.

Totally 467 bacteria and 55 fungi were isolated during P. haitanensis cultivation. The diversity of fungi was smaller than that of bacteria. The bacteria were classified into 41 genera, belonging to Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. The dominant bacterial communities were Alphaproteobacteria and Gammaproteobacteria. Most of the fungi were classified into Ascomycota, only one strain belonging to the Basidiomycota, Agaricomycetes. Bacteria of 19 specific genera were isolated from P. haitanensis while 13 specific genera were isolated from the surrounding seawater. Most actinomycetes and fungi were isolated from the conchocelis cultured indoors, which was different from the microbial communities of the thalli in intertidal zone. Within the isolated microbes, we found that some strains had very high similarity with those pathogens such as Cobetia marina (C. marina, P. haitanensis red-rotting disease), Phoma porphyrae (P. yezoensis disease) and saprotrophic fungi Fusarium sp. and Aspergillus sp..

The diversity of Pyropia phycoshpere microbes during cultivation was affected by the seaweed morphology, culture time and environmental factors. The strains that shared high similarity with Pyropia pathogens were found in this study, which would cause our great attention to these potential pathogens for Pyropia diseases.