Caracterización genética de factores de virulencia en Photobacterium damselae: bases moleculares de la actividad hemolítica

La bacteria marina Photobacterium damselae comprende dos subespecies, la subsp. piscicida y la subsp. damselae. Ambas subespecies presentan características fenotípicas claramente diferenciales. Dichas diferencias abarcan desde diferentes temperaturas de crecimiento o rango de hospedadores hasta una gran variabilidad en la composición de los productos extracelulares. Todas las cepas de P. damselae producen sideróforos, y la naturaleza química de los mismos difiere en las dos subespecies. Aunque no hemos podido descifrar la base genética que se esconde tras estos sistemas, sí hemos encontrado genes regulados por hierro. La mutación de los genes fhuE y de la O-metiltransferasa no causó disminución en la capacidad de crecimiento en déficit de hierro, lo que sugiere una redundancia de sus funciones. Cabe destacar que el gen de la O-metiltransferasa se halla regulado fuertemente por la disponibilidad de hierro extracelular a través de la proteína Fur

Cytotoxin- and chemotaxis-genes cooperate to promote adhesion of photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae (Pdd) is an emerging pathogen of marine animals that sometimes causes serious infections in humans. Two related pore forming toxins, phobalysins P and C, and damselysin, a phospholipase D, confer strong virulence of Pdd in mice. Because infections by Pdd are typically caused following exposure of wounds to sea water we investigated how salinity impacts toxin activity, swimming, and association of Pdd with epithelial cells. These activities were low when bacteria were pre-cultured in media with 3.5% NaCl, the global average salinity of sea water. In contrast, lower salinity increased swimming of wild type Pdd peaking at 2% NaCl, hemolysis, and association with epithelial cells peaking at 1–1.5%. Previously, we have found that hemolysin genes enhance the association of Pdd with epithelial cells, but the underlying mechanisms have remained ill-defined. We here searched for potential links between hemolysin-production, chemotaxis and association of Pdd with target cells at varying salt concentrations. Unexpectedly, disruption of chemotaxis regulator cheA not only affected bacterial swimming and association with epithelial cells at intermediate to low salinity, but also reduced the production of plasmid-encoded phobalysin (PhlyP). The results thus reveal unforeseen links between chemotaxis regulators, a pore forming toxin and the association of a marine bacterium with target cellsThe work was supported by an intramural grant of the University Medical Center Mainz to AR. Work in the CO laboratory is supported by grant AGL2016-79738-R (AEI/FEDER, EU) from the State Agency for Research (AEI) of Spain, and co-funded by the FEDER Program from the European UnionS