Vibrio vulnificus is an autochthonous inhabitant of coastal marine environments where predation by protozoa is a shaping force in the evolution of antiprotozoal mechanisms. These protective mechanisms may also function as virulence factors in animal and human hosts. This study investigates the grazing resistance mechanisms expressed by V. vulnificus against protozoa and the potential role of these antiprotozoal factors in providing fitness in the environment.
The resistance to predation by Tetrahymena pyriformis of clinical and environmental isolates of V. vulnificus with different genotypes was evaluated. The resistance of planktonic cells of V. vulnificus isolates to predation by T. pyriformis was investigated by determining the numbers of planktonic cells after exposure to T. pyriformis. Data shows that place of isolation or genotype did not correlate with grazing resistance of V. vulnificus isolates. However, an oyster isolate, V. vulnificus Env1, showed significant grazing resistance and toxicity towards T. pyriformis.
The whole genome sequence of Env1 was completed, annotated and compared to grazing sensitive strains to identify Env1 unique features that may contribute to grazing resistance. These unique genes include a putative internalin, a putative rearrangement hotspot toxin (rhs), an ankyrin protein, a type 1 secretion system-associated agglutinin RTX membrane protein and a suppressor for copper-sensitivity ScsD. In order to assess the role of these genes in grazing resistance, site-directed mutagenesis was performed and mutants were exposed to predation by different protozoan models. We will discuss the role of each of these genes in predation resistance of V. vulnificus.