Dynamics ofVibrioPopulations and Their Role in Environmental Nutrient Cycling

Molecular surveys of bacterioplankton communities in coastal regions and open oceans have yielded similar 16S rRNA sequences, although coastal sites can differ significantly from the open ocean with respect to primary production rates and terrestrial influence. While obligate “ultramicrobacteria” have been described from oligotrophic open ocean environments and hypothesized to substantially contribute to environmental nutrient cycling, the extent to which facultative “ultra-micro” Vibrio cells contribute to microbial diversity and nutrient cycling in oligotrophic environments has not been addressed; this may reflect the limitation of DNA-based studies that are based on a collection of planktonic biomass on a 0.2-μm-pore-size filter. Association with larger host organisms may mediate the environmental dynamics of symbiotic or commensal Vibrio populations. Chitinase activity may reflect one of the most important extracellular enzymatic processes in the marine environment. A facultatively anaerobic bacterium originally described as a denitrifying Vibrio was recently classified as an alphaproteobacterium based upon DNA sequence data. Comparative genomic approaches between nonpathogens and pathogenic strains can help explain the unifying themes underlying bacterial-host interactions and mechanisms by which pathogenic interactions may emerge. Environmental genomic approaches to explore the metabolic diversity associated with phylogenetic clades can shed light on how widespread certain features, such as N2 fixation, bioluminescence, and cell signaling, are among the Vibrionaceae and whether vibrios are capable of as-yet- undiscovered metabolic transformations (e.g., denitrification, phototrophy, chemoautotropy). The dynamics and distribution of bacterioplanktonic Vibrio populations are determined by adaptations to environmental gradients, including temperature, salinity, and nutrient concentration.