Microbial communities in coastal seawater during Heterosigma akashiwo and Alexandrium catenella blooms in Chilean Patagonian fjords

Abstract

Harmful algal blooms (HABs) are recurring events in Chilean coasts where free-living and associated microbiota (also known as HAB holobiont) may play a crucial role for occurrence, monitoring and prediction of HAB. Here, we investigated the associated microbial communities with Heterosigma akashiwo and Alexandrium catenella blooms in the Chilean Patagonia fjords by microscopic observations and rRNA metabarcoding sequencing. By microscopic observations, H. akashiwo and A. catenella cells were accompanied by abundant diatoms (Skeletonema) and athecate dinoflagellates, and diatoms (Thalassiosira and Leptocylindrus) and dinoflagellates (Heterocapsa), respectively. By 16S rRNA- and 18S rRNA-based metabarcoding sequencing, our results not only revealed significant differences in richness, diversity, and taxonomic structure of microbial communities between blooms but also between the studied seawater fractions (1 and 0.2 μm). In 18S rRNA-based communities, H. akashiwo bloom was generally dominated by eukaryotic Stramenopiles, Raphidophyceae_X and Heterosigma, while A. catenella bloom was dominated by eukaryotic Alveolata and protists Syndiniales (Dino-Group-I) at the phylum, order, and genus level, respectively. Proteobacteria (Rhodobacteriales), Bacteroidota (Flavobacteriales) and Cyanobacteria (Synechococcales) were dominant taxa in the structure of 16S rRNA-based communities in both blooms and both seawater fractions. Our study also suggested a high and differentiated interaction between 16S rRNA- and 18S rRNA-based microbial communities in both blooms, with the bacteria Blastopirellula and the dinoflagellate Dino-Group-I-Clade-1 as keystone taxa in A. catenella bloom.

Keywords: Bacterioplankton; Harmful algal bloom; Marine microbiome; Phycosphere; Phytoplankton.