g., hydrocarbons and sulfide), and/or for the lower oxygen concentration that results from higher flow of anoxic hydrothermal

fluids. 16S rRNA gene sequences obtained from single filaments have shown that Guaymas Basin Beggiatoaceae belong to several distinct lineages within a clade of large, vacuolated, nitrate-accumulating, sulfur-oxidizing filamentous bacteria found on sulfidic sediments at hydrothermal vents, hydrocarbon seeps, coastal upwelling regions, and in freshwater environments with seasonal or permanent oxygen depletion. They may belong to two or more candidate genus-level groups ( MacGregor et al., 2013a) in a recently proposed reorganization of the family Beggiatoaceae ( Salman et al., 2011). None of these bacteria are available in pure culture. The results of physiological studies of orange filaments collected from mat material have been consistent with a nitrate-reducing, sulfur-oxidizing metabolism ( McHatton et

al., 1996 and Otte et Transmembrane Transporters modulator al., 1999), again with the caveat that the filament surfaces host a diverse microbial assemblage that is difficult to remove entirely. The orange Guaymas Beggiatoaceae accumulate nitrate intracellularly ( McKay et al., 2012 and McHatton et al., 1996), likely within their vacuoles, as has been observed or postulated for other larger-diameter ( de Albuquerque et al., EPZ5676 2010 and Hinck et al., 2007) filaments. Orange filaments examined by epifluorescence microscopy during our 2008 and 2009 cruises had a diameter of ~ 35 μm, corresponding to the 25–35 μm size class reported from repeated earlier sampling ( Nelson et al., 1989). The orange color appears to be due to the abundant production of one or more c-type cytochromes ( Nikolaus et al., 2003, Prince et al., 1988 and MacGregor et al., 2013b). In order to better understand the physiology of these uncultured bacteria, a single orange Guaymas Beggiatoa (Cand. Maribeggiatoa)

filament was isolated and purified for genomic sequencing. We have previously reported on evidence for the purity and completeness of the genome, and possible mobile elements suggesting a history of genetic exchange with other filamentous bacteria, including cyanobacteria ( MacGregor et al., 2013a); and on genome-enabled identification of an abundant orange cytochrome which appears to be responsible for the http://www.selleck.co.jp/products/erastin.html visible difference between white and orange filaments ( MacGregor et al., 2013b). Here, we consider the possible sulfide oxidation, nitrate respiration, carbon acquisition, and energy conservation pathways encoded by this genome (referred to as the BOGUAY sequence), and discuss possible roles for the cytochrome identified earlier. The possible nitrate respiration pathways are compared to those of the three other Beggiatoaceae draft and partial genomes available to date, and phylogenetic reconstructions are presented for putative enzymes of the Calvin–Benson–Bassham (CBB) cycle and the oxidative and reductive tricarboxylic acid cycles (TCA and rTCA, respectively).