Halophilic Bacteriovorax (Bx), formerly known as the marine Bdellovibrio, are Gram-negative, predatory bacteria found in saltwater systems. To assess their genetic diversity and geographical occurrence, the small subunit rRNA (ssu-rRNA) gene sequences were analysed from 111 marine, salt lake and estuarine isolates recovered from 27 locations around the world. Phylogenetic analysis of these isolates using Geobacter as the outgroup revealed eight distinct ribotype clusters each with at least two isolates. Each cluster was composed of isolates with >or= 96.5% similarity in ssu-rRNA sequences. Three single isolate outliers were observed. Many of the Bx ribotypes were widely dispersed among different types of ecosystems (e.g. cluster III was recovered from the Great Salt Lake, the Atlantic Ocean, Pacific Ocean, Chesapeake Bay and gills of aquarium fish). However, cluster V was only recovered from a single ecosystem, estuaries. Cluster V was originally detected in the Chesapeake Bay and subsequently in the Pamlico Sound/Neuse River system. Principal coordinate analysis revealed that the sequences of the isolates from different environments were distinct from each other. The results of this study reveal the saltwater Bx to be phylogenetically and environmentally more diverse than was previously known.

In aquatic systems, bacterial community succession is a function of top-down and bottom-up factors, but little information exists on ''sideways'' controls, such as bacterial predation by Bdellovibriolike organisms (BLOs), which likely impacts nutrient cycling within the microbial loop and eventual export to higher trophic groups. Here we report transient response of estuarine microbiota and BLO spp. to tidal-associated dissolved organic matter supply in a riverdominated estuary, Apalachicola Bay, Florida. Both dissolved organic carbon and dissolved organic nitrogen concentrations oscillated over the course of the tidal cycle with relatively higher concentrations observed at low tide. Concurrent with the shift in dissolved organic matter (DOM) supply at low tide, a synchronous increase in numbers of bacteria and predatorial BLOs were observed. PCR-restriction fragment length polymorphism of small subunit rDNA, cloning, and sequence analyses revealed distinct shifts such that, at low tide, significantly higher phylotype abundances were observed from ␥-Proteobacteria, ␦-Proteobacteria, Bacteroidetes, and high G؉C Gram-positive bacteria. Conversely, diversity of ␣-Proteobacteria, ␤-Proteobacteria, and ChlamydialesVerrucomicrobia group increased at high tides. To identify metabolically active BLO guilds, tidal microcosms were spiked with six 13 C-labeled bacteria as potential prey and studied using an adaptation of stable isotope probing. At low tide, representative of higher DOM and increased prey but lower salinity, BLO community also shifted such that mesohaline clusters I and VI were more active; with an increased salinity at high tide, halotolerant clusters III, V, and X were predominant. Eventually, 13 C label was identified from higher micropredators, indicating that trophic interactions within the estuarine microbial food web are potentially far more complex than previously thought.Bdellovibrio-like organisms (BLOs) ͉ dissolved organic matter ͉ predator-prey interactions ͉ stable isotope probing ͉ tidal microbiota M arine dissolved organic matter (DOM) is one of the largest active reservoirs of reduced carbon at the earth's surface and, to a large extent, as the primary consumers of this DOM, bacteria control its fate via assimilation and/or remineralization processes (1, 2). The fate of DOM is a also a function of physiologic status and taxonomic composition of the autochthanous microbiota as well as the relative DOM lability supplied to the system, all of which vary both spatially and temporally in response to physiochemical conditions (1, 3, 4). DOM that is assimilated into bacterial biomass is potentially available for trophic transfer via the microbial loop (5) and as such must be accounted for in estimates of marine carbon flux.Bacterial groups that mineralize DOM are taxonomically diverse (2, 3, 6), which is often a function of niche variability (1-3). Specifically, estuarine systems exhibit high spatiotemporal and physiochemical variability, often resulting in short-lived blooms of some bacterial spp....

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Microbiol. 68:6129-6137, 2002). The present study utilized a combination of culture-and non-culture-based approaches to study differences in composition of assemblages of syntrophic and methanogenic microbial communities in eutrophic, transition, and oligotrophic areas along the phosphorus gradient. Methanogenesis rates were much higher in eutrophic and transition regions, and sequence analysis of 16S rRNA gene clone libraries constructed from samples taken from these regions revealed differences in composition and activities of syntroph-methanogen consortia. Methanogens from eutrophic and transition regions were almost exclusively composed of hydrogenotrophic methanogens, with approximately 10,000-fold-greater most probable numbers of hydrogenotrophs than of acetotrophs. Most cultivable strains from eutrophic and transition regions clustered within novel lineages. In non-culture-based studies to enrich syntrophs, most bacterial and archaeal clones were either members of novel lineages or closely related to uncultivated environmental clones. Novel cultivable Methanosaeta sp. and fatty acid-oxidizing bacteria related to the genera Syntrophomonas and Syntrophobacter were observed in microcosms containing soil from eutrophic regions, and different lines of evidence indicated the existence of novel syntrophic association in eutrophic regions.