Environmental Heterogeneity Drives Ecological Differentiation in Vibrio Populations Across Subtropical Marine Habitats.

Elucidating how environmental gradients structure bacterial communities remains fundamental to microbial ecology. We investigated Vibrio population dynamics across contrasting subtropical marine environments in Hong Kong over a year period. Using an integrated approach combining cultivation techniques with molecular analyses of Hsp60 and 16S rRNA genes, we characterised the population structure between a coastal site (Clear Water Bay) and an estuarine site (Deep Bay). The estuarine environment consistently harboured higher Vibrio abundances (10-10 copies/mL) compared to coastal waters (10-10 copies/mL), with significantly greater phylogenetic diversity. Multivariate analyses revealed salinity as the primary driver of community differentiation between sites, while temperature governed seasonal succession patterns. Phylogenetic analysis of 1521 Vibrio isolates identified three distinct ecological groups corresponding to specific temperature-salinity niches, with evidence of habitat-specific thermal adaptations among closely related strains. Experimental characterisation of thermal performance curves confirmed physiological differentiation between warm- and cool-temperature adapted strains despite high genetic similarity (> 97% Hsp60 gene sequence identity). Several abundant species detected via amplicon sequencing (including V. navarrensis and V. mimicus) displayed site-specific ecotypes but remained uncultivated, highlighting methodological constraints in community characterisation. Our findings demonstrate how environmental heterogeneity drives fine-scale ecological differentiation in Vibrio populations, providing insights into mechanisms of bacterial adaptation in dynamic marine environments.