Symbiotic associations and pathogenic potential of Vibrios in the North Inlet Estuary

Abstract

Salt marshes along the South Eastern US coast are largely dominated by the macrophytes Spartina alterniflora (Loisel) and Juncus roemerianus (Scheele) which form vast stands with robust, interconnecting root systems and contribute to sediment accretion, functioning to shape intertidal zones. Large stands of these grasses are punctuated by mud flats and infaunal burrows of the fiddler crabs Uca pugnax (Bosc) and Uca pugilator (Smith); the feeding and burrowing actions of which, serve to ventilate and redistribute the marsh sediment. Bacteria belonging to the genus Vibrio are flagellated gram negative rods or curved rods common throughout marine systems. Vibrios inhabit a range of niches within the water column, attached to sediment particles and in symbiotic associations with marine animals and plants. Most commonly though, vibrios are known for their pathogenic nature and are the causative agents of many diseases of humans and other animals. In general, vibrios are understudied in natural systems free of anthropogenic influence. This investigation examined the physiological activities, biogeography and pathogenic potential of Vibrionaceae from the pristine intertidal North Inlet, SC saltmarsh. The ability of several Vibrio species isolated from S. alterniflora and J. roemerianus rhizoplanes; to synthesize the phytohormone indole-3 acetic acid via the indole-3-acetamide pathway was elucidated and quantified. An extensive study of the density and biogeography of Vibrionaceae in sediment, burrow and water microniches was conducted and a collection of 186 presumptive Vibrio parahaemolyticus strains was isolated. Sediment microenvironments were found overall to harbor the highest density (480,000 CFUs mL^-1 in the S. alterniflora growth zone) of presumptive V. parahaemolyticus and Vibrionaceae in general. A randomly selected sub-group of these strains was further characterized physiologically and phylogenetically. Presumptive V. parahaemolyticus strains were screened for the species specific marker thermolabile hemolysin (tlh) and the human virulence marker genes thermostable direct hemolysin (tdh) and thermostable direct hemolysin-related hemolysin (trh). Newly designed primers were employed for PCR reactions targeting tdh and trh which were found to be substantially more effective than older commonly employed primers. The genes encoding TDH and TRH were present in 41% and 7.3% of the Vibrionaceae strains examined shifting the paradigm of conventional wisdom on this subject.