Microbiota of the Digestive Gland of Red Abalone (Haliotis rufescens) Is Affected by Withering Syndrome.

Alejandro Villasante,Jaime Romero,Rodrigo Rojas,Natalia Catalán,Karin B Lohrmann

doi:10.3390/microorganisms8091411

Abstract

Withering syndrome (WS), an infectious disease caused by intracellular bacteria Candidatus Xenohaliotis californiensis, has provoked significant economic losses in abalone aquaculture. The pathogen infects gastroenteric epithelia, including digestive gland, disrupting the digestive system and causing a progressive wilting in abalone. Nonetheless, our knowledge about WS implications in digestive gland microbiota, and its role in diseases progress remains largely unknown. This study aims to determine whether digestive gland-associated microbiota differs between healthy red abalone (Haliotis rufescens) and red abalone affected with WS. Using high-throughput sequencing of the V4 region of the 16S rRNA gene, our results revealed differences in microbiota between groups. Bacterial genera, including Mycoplasma, Lactobacillus, Cocleimonas and Tateyamaria were significantly more abundant in healthy abalones, whilst Candidatus Xenohaliotis californiensis and Marinomonas were more abundant in WS-affected abalones. Whilst Mycoplasma was the dominant genus in the healthy group, Candidatus Xenohaliotis californiensis was dominant in the WS group. However, Candidatus Xenohaliotis californiensis was present in two healthy specimens, and thus the Mycoplasma/Candidatus Xenohaliotis californiensis ratio appears to be more determinant in specimens affected with WS. Further research to elucidate the role of digestive gland microbiota ecology in WS pathogenesis is required.

Highlights

In Chile, aquaculture has become one of the larger food productive sectors, with a sustained expansion rate that has positioned the country in the top ten major aquaculture producers worldwide [1]
306,616 reads were measured in the group of healthy red abalones and 339,477 reads were measured in the group of red abalones with Withering syndrome (WS)
It has been said that the causative agent is a rickettsia-like organism known as Candidatus Xenohaliotis californiensis, which initially infects the epithelium of the gastroenteric system followed by a progressive deterioration in the mussel pedal muscle [5,10]

Summary

Introduction

In Chile, aquaculture has become one of the larger food productive sectors, with a sustained expansion rate that has positioned the country in the top ten major aquaculture producers worldwide [1]. Some infectious diseases have their origin in the disruption of the established community structure and subsequent function changing the overall balance between the microbiota and host, resulting in altered infection susceptibility [8] Taking this antecedent into account, it is of interest to determine whether WS affects the composition of digestive tract microbiota in abalone, since this is a first step to elucidate how does microbial community respond to WS. Knowing this aspect of the disease can contribute to a better understanding of the pathogenesis of WS as well as help to implement strategies, including the use of probiotics and/or prebiotics to improve growth performance, inhibition of adherence and colonization of pathogenic bacteria, immune response and WS resistance in red abalone farming

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