Ecological stability and plasticity of culture associated bacterial communities from distinct strains of the benthic dinoflagellate <i>Coolia malayensis</i>

<p style="line-height: 1.6;"> Dinoflagellate harbors diverse associated bacterial communities (ABCs) that play crucial roles in host physiology and ecological interactions. <i>Coolia malayensis</i> is a benthic dinoflagellate distributed from temperate to tropical regions. Despite growing knowledge about the morphology, distribution, and toxicity of <i>C. malayensis</i>, little is known about its associated bacteria, particularly under changing environmental conditions. Given that climate change alters microbial interactions through temperature shifts, this study investigated the composition, diversity, and dynamics of ABCs across four <i>C. malayensis</i> strains, under varying temperatures and growth time. Despite differences in strain origin, a stable core microbiome, comprising <i>Alteromonas</i>, <i>Marinobacter</i>, <i>Muricauda</i>, and <i>Ruegeria</i>, was consistently observed, suggesting these taxa are functionally important members of the ABC. However, strain-specific differences and temperature-driven shifts were also detected, especially among low-abundance bacterial taxa. Negative interactions among abundant amplicon sequence variants, such as those between <i>Ruegeria</i> and <i>Muricauda</i>, and between <i>Alteromonas</i> and <i>Marinobacter</i>, were conserved across conditions, suggesting stable patterns of co-occurrence. Functional predictions and Kyoto Encyclopedia of Genes and Genomes pathway analysis suggested potential involvement of ABCs in chemoheterotrophy, fermentation, hydrocarbon degradation, energy metabolism, and the metabolism of cofactors and vitamins, implying potential diverse metabolic exchanges between the bacteria and <i>C. malayensis</i>. These findings highlight both the ecological stability and environmental sensitivity of <i>C. malayensis</i> culture-associated microbiomes, with important implications for host health and ecosystem dynamics under climate change. </p>