Novel microbiome dominated by Arcobacter during anoxic excurrent flow from an ocean blue hole in Andros Island, The Bahamas.

Andros Island, The Bahamas, composed of porous carbonate rock, has about 175 inland blue holes and over 50 known submerged ocean caves along its eastern barrier reef. These ocean blue holes can have both vertical and horizontal zones that penetrate under the island. Tidal forces drive water flow in and out of these caves. King Kong Cavern has a vertical collapse zone and a deep penetration under Andros Island that emits sulfidic, anoxic water and masses of thin, mucoid filaments ranging to meters in length and off-white turbid water during ebb flow. Our objective was to determine the microbial composition of this mucoid material and the unconsolidated water column turbidity based on the concept that they represent unique lithoautotrophic microbial material swept from the cave into the surrounding ocean. Bacterial DNA extracted from these filaments and surrounding turbid water was characterized using PCR that targeted a portion of the 16S rRNA gene. The genus Arcobacter dominated both the filaments and the water column above the cave entrance. Arcobacter nitrofigilis and Arcobacter sp. UDC415 in the mucoid filaments accounted for as much as 80% of mapped DNA reads. In the water column Arcobacter comprised from 65% to over 85% of the reads in the depth region from about 18 m to 34 m. Bacterial species diversity was much higher in surface water and in water deeper than 36 m than in the intermediate zone. Community composition indicates that ebb flow from the cavern influences the entire water column at least to within 6 m of the surface and perhaps the near surface as well.

Dual-Label Radioisotope Method for Simultaneously Measuring Bacterial Production and Metabolism in Natural Waters.

Bacterial production and amino acid metabolism in aquatic systems can be estimated by simultaneous incubation of water samples with both tritiated methyl-thymidine and C-labeled amino acids. This dual-label method not only saves time, labor, and materials, but also allows determination of these two parameters in the same microbial subcommunity. Both organic carbon incorporation and respiration can be estimated. The results obtained with the dual-label technique are not significantly different from single-radiolabel methods over a wide range of bacterial activity. The method is particularly suitable for large-scale field programs and has been used successfully with eutrophic estuarine samples as well as with oligotrophic oceanic water. In the mesohaline portion of Chesapeake Bay, thymidine incorporation ranged seasonally from 2 to 635 pmol liter h and amino acid turnover rates ranged from 0.01 to 28.4% h. Comparison of thymidine incorporation with amino acid turnover measurements made at a deep, midbay station in 1985 suggested a close coupling between bacterial production and amino acid metabolism during most of the year. However, production-specific amino acid turnover rates increased dramatically in deep bay waters during the spring phytoplankton bloom, indicating transient decoupling of bacterial production from metabolism. Ecological features such as this are readily detectable with the dual-label method.