Bacterial Composition Associated With Giant Colonies of the Harmful Algal Species Phaeocystis globosa.

Zhu Zhu,Hai Doan-Nhu,Xinjun Jiang,Rui Meng,Lam Nguyen-Ngoc,Walker O. Smith Jr.

doi:10.3389/fmicb.2021.737484

Abstract

The cosmopolitan algae Phaeocystis globosa forms harmful algal blooms frequently in a number of tropical and subtropical coastal regions in the past two decades. During the bloom, the giant colony, which is formed by P. globosa, is the dominant morphotype. However, the microenvironment and the microbial composition in the intracolonial fluid are poorly understood. Here, we used high-throughput 16S rRNA amplicon sequencing to examine the bacterial composition and predicted functions in intracolonial fluid. Compared with the bacterial consortia in ambient seawater, intracolonial fluids possessed the lower levels of microbial richness and diversity, implying selectivity of bacteria by the unique intracolonial microenvironment enclosed within the P. globosa polysaccharide envelope. The bacterial consortia in intracolonial fluid were dominated by Balneola (48.6% of total abundance) and Labrezia (28.5%). The bacteria and microbial function enriched in intracolonial fluid were involved in aromatic benzenoid compounds degradation, DMSP and DMS production and consumption, and antibacterial compounds synthesis. We suggest that the P. globosa colonial envelope allows for the formation of a specific microenvironment; thus, the unique microbial consortia inhabiting intracolonial fluid has close interaction with P. globosa cells, which may benefit colony development.

Highlights

Phaeocystis globosa is a cosmopolitan marine phytoplankton that plays important roles in carbon and sulfur biogeochemical cycles (Schoemann et al, 2005)
As the intracolonial fluid samples exacted from P. globosa colonies were mixture of microbiota and P. globosa cells, co-amplification of chloroplast DNA by 338F-806R was observed and resulted in 92.1% operational taxonomic units (OTUs) annotated as P. globosa chloroplast DNA in intracolonial fluid samples (Supplementary Figure S1)
A total of 108,764 highquality 16S rRNA sequences were obtained from seawater samples (n = 3) and intracolonial fluid samples (n = 3)

Summary

Introduction

Phaeocystis globosa is a cosmopolitan marine phytoplankton that plays important roles in carbon and sulfur biogeochemical cycles (Schoemann et al, 2005). Blooms of P. globosa in temperate regions, especially in the North Sea, have been observed regularly since the 1970s and are associated with nutrient enrichment from rivers (Cadee and Hegeman, 2002). Outbreaks of P. globosa blooms have been reported in tropical and subtropical regions frequently in the past two decades, including coastal waters of China (Qi et al, 2004), Viet Nam (Tang et al, 2004; Doan-Nhu et al, 2010; Smith et al, 2014) and the Arabian Sea (Madhupratap et al, 2000). A unique feature of Phaeocystis is its polymorphic life cycle, which includes free-living solitary cells and colonies. A colony is balloon-like, with an envelope consisting of mucilaginous

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Results

Conclusion