AUTHOR=Hu Lidan , Peng Xingyue , Zhou Jingyan , Zhang Yanmei , Xu Shanghui , Mao Xiaomei , Gao Yahui , Liang Junrong 

TITLE=Characterizing the Interactions Among a Dinoflagellate, Flagellate and Bacteria in the Phycosphere of Alexandrium tamarense (Dinophyta)

JOURNAL=Frontiers in Marine Science

VOLUME=2

YEAR=2015

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2015.00100

DOI=10.3389/fmars.2015.00100

ISSN=2296-7745

ABSTRACT=<p>A small flagellate alga was isolated from the phycosphere of a toxic red tide dinoflagellate <italic>Alexandrium tamarense</italic>. Phylogenetic analysis and ultrastructural observations demonstrated that the small flagellate alga is a species belong to Ochrophyte <italic>Ochromonas</italic> sp. The process of ingesting bacteria by <italic>Ochromonas</italic> sp. was recorded by a time lapse capture under a light microscope. Through the use of different assemblages in the co-culture experiment, the species interactions in this phycosphere microenvironment were analyzed. We demonstrated that the growth of <italic>Ochromonas</italic> sp. was supported by bacteria. Three strains of bacteria ingested by <italic>Ochromonas</italic> sp. were isolated and identified to belong to α-, δ- and γ-Proteobacteria. The growth of <italic>A. tamarense</italic> was suppressed when co-cultured with bacteria. In contrast, <italic>Ochromonas</italic> sp. triggered the growth of <italic>A. tamarense</italic> by inhibiting the growth of algicidal bacteria. This result firstly demonstrated a positive effect of a flagellate on a dinoflagellate in the phycosphere of <italic>A. tamarense</italic>. Combined with other negative effects between dinoflagellates and bacteria or bacteria and flagellates, this study showed a series of clear interactions among dinoflagellate, bacterium, and flagellate in the dinoflagellate microenvironment.</p>