Jewfish Sink is a former anchialine karst feature located in the Gulf of Mexico off the coast of West Central Florida. Freshwater flowed from the feature until 1962 and it is now an anoxic marine basin. The current biodiversity within Jewfish Sink was examined in terms of Bacteria, Archaea, and Eukaryota using a combination of 16S and 18S ribosomal RNA analysis from environmental samples. Analysis of 16S rRNA sequences from microbial mats in the anoxic zones revealed a broad diversity of bacteria (265 clones) and archaea (392 clones), many of which had previously been identified in anoxic environmental samples and are likely to be involved with sulfur, nitrogen, and methane metabolism. Sequence analysis of 785 18S clones revealed that fungi and dinoflagellate sequences dominate the eukaryote sequences. Because Jewfish Sink water is anoxic and high in sulfide, we investigated the effect of Jewfish Sink on the nearby shallow benthic environment. We compared the shallow benthic macrofauna near Jewfish Sink with that near Crystal Beach Spring, an active submarine spring. We found significantly greater species richness, abundance, and diversity of benthic fauna near the Jewfish Sink site than near Crystal Beach Spring. This comparison suggests that greater submarine groundwater discharge in an area with active submarine springs is a significant factor reducing the richness and diversity of the benthic community structure in the nearshore, shallow marine environment.

The genome sequence of the obligate chemolithoautotroph Hydrogenovibrio crunogenus paradoxically predicts a complete oxidative citric acid cycle (CAC). This prediction was tested by multiple approaches including whole cell carbon assimilation to verify obligate autotrophy, phylogenetic analysis of CAC enzyme sequences and enzyme assays. Hydrogenovibrio crunogenus did not assimilate any of the organic compounds provided (acetate, succinate, glucose, yeast extract, tryptone). Enzyme activities confirmed that its CAC is mostly uncoupled from the NADH pool. 2-Oxoglutarate:ferredoxin oxidoreductase activity is absent, though pyruvate:ferredoxin oxidoreductase is present, indicating that sequence-based predictions of substrate for this oxidoreductase were incorrect, and that H. crunogenus may have an incomplete CAC. Though the H. crunogenus CAC genes encode uncommon enzymes, the taxonomic distribution of their top matches suggests that they were not horizontally acquired. Comparison of H. crunogenus CAC genes to those present in other 'Proteobacteria' reveals that H. crunogenus and other obligate autotrophs lack the functional redundancy for the steps of the CAC typical for facultative autotrophs and heterotrophs, providing another possible mechanism for obligate autotrophy.

The biocomplexity of sediment communities along a 120 m transect near an arsenic-rich, shallow marine hydrothermal vent at Tutum Bay, Papua New Guinea was thoroughly examined. A count of macro-and meiofaunal organisms was combined with bacterial and eukaryotic SSU rRNA gene surveys to assess biodiversity. Each site along the transect had distinct microbial communities. Near-vent sites were more similar to each other than sites further from the vent. Some species, such as Ignavibacterium, Caldilinea, and Capitella were only found near-vent. Biodiversity generally increased with distance from the vent. The community composition responded to the presence of hydrothermal fluids with a clear correlation between temperature and thermophilic organisms. Primary production appeared to be a mix of chemo-and phototrophy. Association analyses suggest many potential interactions between organisms occur at certain sites, and that species distributions and interactions occur in the context of complex spatial relationships related to the geochemistry of the hydrothermal vent fluids. While Tutum Bay is heavily influenced by arsenic, no specific correlation between bacteria that metabolize arsenic and the concentration of different oxidation states of arsenic ions was observed, perhaps because very little of the arsenic present was bioavailable. The observed homogeneous distribution of arsenic reducers along the transect could be due to background arsenic metabolism. This study represents a holistic study of biocomplexity on a broad phylogenetic range across a 120 m transect associated with a marine shallow-water hydrothermal vent.Subject Category: Microbial ecology and functional diversity of natural habitats.

There is an error in the Author contributions statement. The first sentence (JG was the PI of the grant that supported this project.) should be deleted.The second sentence should read: JG participated in the planning, field work, analysis, and writing of the manuscript.