Volcanic caves are filled with colorful microbial mats on the walls and ceilings. These volcanic caves are found worldwide, and studies are finding vast bacteria diversity within these caves. One group of bacteria that can be abundant in volcanic caves, as well as other caves, is Actinobacteria. As Actinobacteria are valued for their ability to produce a variety of secondary metabolites, rare and novel Actinobacteria are being sought in underexplored environments. The abundance of novel Actinobacteria in volcanic caves makes this environment an excellent location to study these bacteria. Scanning electron microscopy (SEM) from several volcanic caves worldwide revealed diversity in the morphologies present. Spores, coccoid, and filamentous cells, many with hair-like or knobby extensions, were some of the microbial structures observed within the microbial mat samples. In addition, the SEM study pointed out that these features figure prominently in both constructive and destructive mineral processes. To further investigate this diversity, we conducted both Sanger sequencing and 454 pyrosequencing of the Actinobacteria in volcanic caves from four locations, two islands in the Azores, Portugal, and Hawai'i and New Mexico, USA. This comparison represents one of the largest sequencing efforts of Actinobacteria in volcanic caves to date. The diversity was shown to be dominated by Actinomycetales, but also included several newly described orders, such as Euzebyales, and Gaiellales. Sixty-two percent of the clones from the four locations shared less than 97% similarity to known sequences, and nearly 71% of the clones were singletons, supporting the commonly held belief that volcanic caves are an untapped resource for novel and rare Actinobacteria. The amplicon libraries depicted a wider view of the microbial diversity in Azorean volcanic caves revealing three additional orders, Rubrobacterales, Solirubrobacterales, and Coriobacteriales. Studies of microbial ecology in volcanic caves are still very limited. To rectify this deficiency, the results from our study help fill in the gaps in our knowledge of actinobacterial diversity and their potential roles in the volcanic cave ecosystems.

The diversity and distribution of a bacterial community from Coffee Pots Hot Spring, a thermal spring in Yellowstone National Park with a temperature range of 39.3 to 74.1°C and pH range of 5.75 to 6.91, were investigated by sequencing cloned PCR products and quantitative PCR (qPCR) of 16S rRNA and metabolic genes. The spring was inhabited by three Aquificae genera-Thermocrinis, Hydrogenobaculum, and Sulfurihydrogenibium-and members of the Alpha-, Beta-, and Gammaproteobacteria, Firmicutes, Acidobacteria, Deinococcus-Thermus, and candidate division OP5. The in situ chemical affinities were calculated for 41 potential metabolic reactions using measured environmental parameters and a range of hydrogen and oxygen concentrations. Reactions that use oxygen, ferric iron, sulfur, and nitrate as electron acceptors were predicted to be the most energetically favorable, while reactions using sulfate were expected to be less favorable. Samples were screened for genes used in ammonia oxidation (amoA, bacterial gene only), the reductive tricarboxylic acid (rTCA) cycle (aclB), the Calvin cycle (cbbM), sulfate reduction (dsrAB), nitrogen fixation (nifH), nitrite reduction (nirK), and sulfide oxidation (soxEF1) by PCR. Genes for carbon fixation by the rTCA cycle and nitrogen fixation were detected. All aclB sequences were phylogenetically related and spatially correlated to Sulfurihydrogenibium 16S rRNA gene sequences using qPCR (R 2 ‫؍‬ 0.99). This result supports the recent finding of citrate cleavage by enzymes other than ATP citrate lyase in the rTCA cycle of the Aquificaceae family. We briefly consider potential biochemical mechanisms that may allow Sulfurihydrogenibium and Thermocrinis to codominate some hydrothermal environments.The Aquificales are a strictly thermophilic bacterial lineage that has been recovered from hydrothermal systems worldwide (9,19,26,42,52,53,59). This lineage has attracted much interest in the last 20 years because of its proposed deep phylogenetic position (10,16,29,49). Culturing of the Aquificales has demonstrated that they are largely chemolithoautotrophs that utilize H 2 to reduce O 2 (Knallgas reaction) (30). However, culturing data are often inadequate to understand natural communities as the availability of metabolic substrates and energy yield depend on factors such as geochemistry and microbial community composition, which vary within and between hydrothermal environments.Although Aquificales are chemolithoautotrophs, culture studies and environmental sampling suggest that they use a diversity of metabolic reactions. Hydrogen oxidation is one of the most exergonic reactions in Aquificales-dominated hot springs in Yellowstone National Park (42, 59), but most species are able to oxidize elemental sulfur, thiosulfate, or ferrous iron and reduce nitrate, ferric iron, arsenate, selenate, selenite, or elemental sulfur in addition to or instead of the Knallgas reaction to yield energy (1, 2, 19, 24, 27, 28, 36, 37, 44-46, 64-66, 69). Furthermore, there is a pattern between the general metabol...

Atmospheric corrosion due to adsorption of water and solutes onto metal and metal oxide surfaces is a critical factor in the long term reliability of electronic devices. To investigate the atomistic mechanisms of corrosion, we used molecular dynamics (MD) simulations to study the structure of water adsorbed onto both boehmite (γ-AlO(OH)) and gold (Au) surfaces and electrolyte adsorption and surface speciation on the boehmite (010) surface. Boehmite forms a thin film on aluminum metal under oxidizing conditions, is hydrophilic, and readily adsorbs water from the atmosphere. In contrast, gold surfaces are hydrophobic, and condensed water does not readily bond with the surface. Our MD simulations were performed using the CLAYFF force field that maintains full flexibility of water and substrate and allows for full energy and momentum transfer among all atoms. The boehmite (010) and gold (111) surfaces were initially simulated with no water present and then with incremental additions of water molecules. The calculations indicate the boehmite (010) surface structure strongly controls the organization of the first monolayer of interfacial water. In contrast, the structure of water on the gold (111) surface is controlled by hydrogen bonding among the water molecules. To investigate Cl− adsorption to the boehmite surface, Na+ and Cl− ions were added to two boehmite−water simulation cells, one with 3.5 monolayers of water on the boehmite surface and the other representing water-saturated conditions. In both scenarios, the addition of NaCl solute disturbed the first monolayer of water adsorbed to the surface. Chloride ions displaced water molecules that were originally bound to the boehmite surface. In contrast, the Na+ ions do not disturb the arrangement of these water molecules. Na+−Cl− pairs were observed to occur on the surface. Both the near-surface water structure and the effects of ion adsorption were similar regardless of the number of monolayers of water present in the simulation cells.

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