Identification of bacteria in enrichment cultures of sulfate reducers in the Cariaco Basin water column employing Denaturing Gradient Gel Electrophoresis of 16S ribosomal RNA gene fragments.

BACKGROUND: The Cariaco Basin is characterized by pronounced and predictable vertical layering of microbial communities dominated by reduced sulfur species at and below the redox transition zone. Marine water samples were collected in May, 2005 and 2006, at the sampling stations A (10°30' N, 64°40' W), B (10°40' N, 64°45' W) and D (10°43'N, 64°32'W) from different depths, including surface, redox interface, and anoxic zones. In order to enrich for sulfate reducing bacteria (SRB), water samples were inoculated into anaerobic media amended with lactate or acetate as carbon source. To analyze the composition of enrichment cultures, we performed DNA extraction, PCR-DGGE, and sequencing of selected bands. RESULTS: DGGE results indicate that many bacterial genera were present that are associated with the sulfur cycle, including Desulfovibrio spp., as well as heterotrophs belonging to Vibrio, Enterobacter, Shewanella, Fusobacterium, Marinifilum, Mariniliabilia, and Spirochaeta. These bacterial populations are related to sulfur coupling and carbon cycles in an environment of variable redox conditions and oxygen availability. CONCLUSIONS: In our studies, we found an association of SRB-like Desulfovibrio with Vibrio species and other genera that have a previously defined relevant role in sulfur transformation and coupling of carbon and sulfur cycles in an environment where there are variable redox conditions and oxygen availability. This study provides new information about microbial species that were culturable on media for SRB at anaerobic conditions at several locations and water depths in the Cariaco Basin.

Biosurfactant production by marine bacterial isolates from the Venezuelan Atlantic Front.

Our purpose was to detect, isolate and characterize tensioactive agents with or without emulsifying activity from marine bacterial strains present in seawater and sediment samples from the Venezuelan Atlantic Front. Biosurfactants found in cell-free supernatants from all cultures presented high surface activity as they were able to reduce the water surface tension from 72 dynes cm(-1) to values between 41.7 and 33.9 dynes cm(-1). However, high indirect CMC values were registered for the most of these compounds (51.4%-56.1% v/v). Culture supernatants from S3 and S29 strains showed highest emulsifying activity in the dispersion assay with diesel oil (absorbance 1.06 and 1.18, respectively), while supernatant from the S10 strain induced the most stable oil-in-water emulsions with 16° and 25°API crude oils. Only culture supernatant from S3 strain was able to produce stable oil-in water emulsions with diesel oil and both type of crude oils.

Denaturing gradient gel electrophoresis analyses of the vertical distribution and diversity of Vibrio spp. populations in the Cariaco Basin.

The Cariaco system is the second largest permanently anoxic marine water body in the world. Its water column is characterized by a pronounced vertical layering of microbial communities. The goal of our study was to investigate the vertical distribution and diversity of Vibrio spp. present in the Cariaco Basin waters using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA fragments. Representatives of the Vibrio genus were detected by nested and direct PCR in seawater at 10 depths. Sequence analyses of 55 DGGE bands revealed that only 11 different operational taxonomic units (OTU) are identified as Vibrio species. Between one and five OTUs were detected at each depth and the most common OTUs were OTU 1 and OTU 2, which phylogenetically clustered with Vibrio chagasii and Vibrio fortis, respectively. OTUs 3 and 4 were only found in the anoxic zone and were identified as Vibrio orientalis and Vibrio neptunius, respectively. Several Vibrio species detected are potentially pathogenic to human, prawns and corals such as Vibrio parahaemolyticus, Vibrio fischeri and Vibrio shilonii. In the Cariaco Basin, different Vibrio species were found to be specific to specific depths strata, suggesting that this genus is a natural component of the microbial communities in this marine redox environment.