Compositional Shifts of Bacterial Communities Associated With Pyropia yezoensis and Surrounding Seawater Co-occurring With Red Rot Disease.

Yong-Wei Yan,Lei Tang,Jie Li,Zhao-Lan Mo,Hui-Chao Yang,Yun-Xiang Mao

doi:10.3389/fmicb.2019.01666

Abstract

Pyropia yezoensis is commercially the most important edible red alga in China, and red rot disease is viewed as one of the major constraints for its cultivation. Microbes within the oomycetic genus Pythium have been reported as the causative agents for this disease; however, little is known about the interactions between the disease and the epiphytic and planktonic bacterial communities. In the present study, bacterial communities associated with uninfected, locally infected, and seriously infected thalli collected from cultivation farms, and within seawater adjacent to the thalli, were investigated using in-depth 16S ribosomal RNA (rRNA) gene sequencing in conjunction with assessing multiple environmental factors. For both thalli and seawater, uninfected and infected communities were significantly different though alpha diversity was similar. Phylogenetic differences between epiphytic bacterial communities associated with P. yezoensis were mainly reflected by the relative changes in the dominant operational taxonomic units (OTUs) assigned as genus Flavirhabdus, genus Sulfitobacter, and family Rhodobacteraceae. The prevalent OTUs in seawater also differed in relative abundance across the communities and were affiliated with diverse taxa, including the phyla Actinobacteria, Verrucomicrobia, and Bacteroidetes, and the classes Alpha- and Gamma-proteobacteria. The differentiation of bacterial communities associated with P. yezoensis and seawater was primarily shaped by reactive silicate (RS) content and salinity, respectively. In particular, 14 potential indicators (two OTUs on P. yezoensis and twelve OTUs in seawater) were identified that significantly differentiated P. yezoensis health statuses and correlated with environmental changes. Overall, the present study provides insights into the alterations of bacterial communities associated with P. yezoensis and surrounding seawater co-occurring with red rot disease. Observed changes were closely associated with health status of algal host, and highlight the potential of using community differentiation to forecast disease occurrence.

Highlights

The red algae Pyropia (Bangiales, Rhodophyta), known as laver, is a globally popular food because of its high nutritional and medical value (Noda et al, 1990; MacArtain et al, 2007; Smith et al, 2010), and Pyropia yezoensis (Ueda) is a species of considerable commercial importance in East Asia
A total of 65 and 336 bacterial operational taxonomic units (OTUs) were obtained for P. yezoensis and seawater samples, respectively, which could be assigned into 5 and 17 phyla, respectively, according to the SILVA database
We provide insights into the compositional shifts of P. yezoensis-associated bacterial communities co-occurring with the outbreak of red rot disease, and the alterations of bacterial communities in the surrounding water column

Summary

Introduction

The red algae Pyropia (Bangiales, Rhodophyta), known as laver, is a globally popular food because of its high nutritional and medical value (Noda et al, 1990; MacArtain et al, 2007; Smith et al, 2010), and Pyropia yezoensis (Ueda) is a species of considerable commercial importance in East Asia. Pyropia species have subsequently been rendered susceptible to several diseases, including red rot disease (Arasaki, 1947; Takahashi, 1977; Ding and Ma, 2005; Lee et al, 2017), Olpidiopsis disease (Arasaki, 1960; Ding and Ma, 2005; Kwak et al, 2017), and green spot disease (Fujita, 1990; Kim et al, 2016) in the blade stage, in addition to yellow spot disease (Guan et al, 2017) and white spot disease (Guan et al, 2013) in the shell-boring conchocelis stage These diseases have caused a significant decline in Pyropia production in recent years, leading to heavy economic losses (Kim et al, 2014). The infection spreads quickly in the farm and leads P. yezoensis rot to different degree, from red patches to numerous small holes on the blades, and the whole cultivation net in a few days, by which time the disease can be observed (Ding and Ma, 2005; Kim et al, 2014)

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