Effects of Ocean Acidification, Hypoxia, and Warming on the Gut Microbiota of the Thick Shell Mussel Mytilus coruscus Through 16S rRNA Gene Sequencing

Menghong Hu,Youji Wang,Hui Kong,Amina Zuberi,Xueqing Chang,Xingzhi Zhang,Jinxia Peng,Fahim Ullah Khan,Yueyong Shang,James K H Fang,Wei Liu

doi:10.3389/fmars.2021.736338

Abstract

Gut microbiota play a very important role in the health of the host, such as protecting from pathogens and maintaining homeostasis. However, environmental stressors, such as ocean acidification, hypoxia, and warming can affect microbial communities by causing alteration in their structure and relative abundance and by destroying their network. The study aimed to evaluate the combined effects of low pH, low dissolved oxygen (DO) levels, and warming on gut microbiota of the mussel Mytilus coruscus. Mussels were exposed to two pH levels (8.1, 7.7), two DO levels (6, 2 mg L−1), and two temperature levels (20, 30°C) for a total of eight treatments for 30 days. The experiment results showed that ocean acidification, hypoxia, and warming affected the community structure, species richness, and diversity of gut microbiota. The most abundant phyla noted were Proteobacteria, Bacteroidetes, and Firmicutes. Principal coordinate analysis (PCoA) revealed that ocean acidification, hypoxia, and warming change microbial community structure. Low pH, low DO, and increased temperature can cause shifting of microbial communities toward pathogen dominated microbial communities. Linear discriminant analysis effect size (LEfSe) showed that the significantly enriched biomarkers in each group are significantly different at the genus level. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis revealed that the gut microbiome of the mussels is associated with many important functions, such as amino acid transport and metabolism, transcription, energy production and conservation, cell wall, membrane and envelope biogenesis, and other functions. This study highlights the complexity of interaction among pH, DO, and temperature in marine organisms and their effects on the gut microbiota and health of marine mussels.

Highlights

The phenomenon in which pH reduction occurs in seawater due to atmospheric CO2 diffusion into the surface waters of oceans is called ocean acidification (Orr et al, 2005)
An operational taxonomic unit (OTU) was classified with a sequence similarity of 97%, and 1,878 operational taxonomic units (OTUs) were identified from gut samples of the mussels
We found that increased temperature, low pH, and low dissolved oxygen (DO) have affected the microbiome diversity, relative abundance and community structure, and composition of gut microbiota populations

Summary

Introduction

The phenomenon in which pH reduction occurs in seawater due to atmospheric CO2 diffusion into the surface waters of oceans is called ocean acidification (Orr et al, 2005). The temperature fluctuations can affect growth, metabolism, and development of marine bivalve mollusks, and in the case of thermal stress conditions, it can cause increased mortality and decreased growth in the bivalve mussels (Dickinson et al, 2012). The digestive physiology and energetic budget of bivalves can be affected by dissolved oxygen concentrations (Wang et al, 2015). The previous studies found that the digestive function and antioxidant response of Mytilus coruscus were affected by hypoxia, acidification, and warming of the ocean (Khan et al, 2020, 2021). It is worth noting that in recent years, more and more scholars have paid attention to the potential combined effects of ocean hypoxia, acidification, and warming on marine life (Sampaio et al, 2021)

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Discussion

Conclusion