Molecular identification and phenotypic characterization of Flavobacterium spp. from Brazilian aquaculture fish.

The genus Flavobacterium comprises several emerging and reemerging fish pathogens responsible for significant economic losses in global aquaculture. In this study, molecular and phenotypic characterization of isolates from Brazilian native fish and tilapia revealed significant taxonomic diversity, with Flavobacterium oreochromis representing most of the isolates (six of eleven isolates). Other identified species included F. davisii, F. indicum, F. inkyongense, and Chryseobacterium indicum, with metadata further linking several atypical isolates to clinical disease. Results showed a clear temperature influence on pathogenicity, with biofilm production and biomass accumulation under both static and agitated conditions being significantly optimized at 28 °C relative to 20 °C and 35 °C. While gliding motility was generally enhanced at 35 °C across the genus, notable phenotypic divergence was observed specifically; F. davisii (strain PiMG24) exhibited a loss of motility at 35 °C, which correlated with a significant increase in biofilm formation. Phylogenetic analysis of 16S rRNA supported distinct species delineation, confirming the presence of multiple emerging pathogens within the Brazilian production chain. These findings demonstrate a high degree of phenotypic plasticity and interspecific variation among Flavobacterium species, highlighting the critical need for sustained epidemiological surveillance to inform targeted biosecurity measures and host-specific vaccine development.