Abstract
Vibrio spp. form a part of the microbiome of copepods—an abundant component of marine mesozooplankton. The biological mechanisms of the Vibrio‐copepod association are largely unknown. In this study we compared biofilm formation of V. cyclitrophicus isolated from copepods (L‐strains related to other particle‐associated strains) and closely related strains originating from seawater (S‐strains), and visualized and quantified their attachment and growth on copepods. The S‐ and L‐strains formed similar biofilms in the presence of complete sea salts, suggesting previously unknown biofilm mechanisms in the S‐strains. No biofilms formed if sodium chloride was present as the only salt but added calcium significantly enhanced biofilms in the L‐strains. GFP‐L‐strain cells attached to live copepods at higher numbers than the S‐strains, suggesting distinct mechanisms, potentially including calcium, support their colonization of copepods. The cells grew on live copepods after attachment, demonstrating that copepods sustain epibiotic V. cyclitrophicus growth in situ. The results demonstrate that in spite of their 99.1% average nucleotide identity, these V. cyclitrophicus strains have a differential capacity to colonize marine copepods. The introduced V. cyclitrophicus—A. tonsa model could be informative in future studies on Vibrio‐copepod association.
Calcium promoted biofilms of Vibrio cyclitrophicus L‐strains relatively more compared to biofilms of closely related S‐strains. GFP‐labelled L‐strains colonized marine copepods more effectively compared to S‐strains and the cells grew epibiotically on live copepods after attachment. The results suggest strain‐level differences in biofilm formation influence bacterial associations with copepods. The results provide insights into the complexity of Vibrio spp. associations with marine animals and particles.