Biofilm development and cell viability: An undervalued mechanism in the persistence of the fish pathogen Tenacibaculum maritimum

Tenacibaculum maritimum is a bacterial pathogen that causes tenacibaculosis outbreaks in major commercial marine fish worldwide. However, scarce knowledge exists regarding T. maritimum life strategies that could act as potential mechanisms for environmental persistence and transmission, such as surface-attached biofilms. This study used high-throughput analyses to quantitatively and qualitatively characterize biofilm formation and activity in T. maritimum strains ACC50.1, PC424.1, PC503.1, and CECT 4276. Additionally, cell-surface properties of the T. maritimum strains, such as hydrophobicity, were determined before inducing biofilm formation. We also briefly examined if pathogenicity against fish varied among T. maritimum strains with differing cell-surface properties. All strains were moderately hydrophobic and rapidly formed biofilms on polystyrene surfaces in a three-step process, with live and dead cells in multilayered-like bacterial aggregates. Virulence in turbot (Scophthalmus maximus) was assessed through a prolonged-immersion challenge. Turbot exhibited the classical signs of tenacibaculosis and mortalities for the T. maritimum strains PC424.1, CECT 4276, and ACC50.1, but no symptoms or mortalities were recorded against PC503.1 or non-challenged controls. Interestingly, while all T. maritimum strains tended to develop profuse biofilms over time, all biofilms showed a decreasing tendency in cell viability. (i.e., a range of fluorescent ratios of live-to-dead sessile cells of ca. 17–51 at 24 h versus 12–22 at 96 h). The fast kinetics of T. maritimum biofilm formation suggests that aquaculture settings can harbor these cellular accretions as transient reservoirs for virulent strains, possibly contributing to tenacibaculosis prevalence to a degree thus far unknown.