The characterized Form II enzymes discriminate less between CO2 and O2 than do Form I enzymes ( Pearce, 2006 and Tabita et al., 2007). Oxygen concentrations in Guaymas Basin mats may be more consistently low than those in tidal mudflats or freshwater ditches; in situ
microelectrode profiles showed O2 concentrations between zero and ~ 25 μM above and within Guaymas mats ( Gundersen et al., 1992). Carbon fixation efficiency may also be of less competitive importance in the deep-sea mat environment, which is abundantly supplied with dissolved inorganic carbon from the underlying sediments ( McKay et al., 2012). Putative genes for two different PPi-dependent 6-phosphofructokinases (00127_3135, 01092_1318) and an H(+)-translocating pyrophosphatase (00848_4300) were identified (Table S4). One of the phosphofructokinases and the pyrophosphatase are most closely related to those from several see more Beggiatoaceae and other Gammaproteobacteria (Fig. S2A, C), including M. capsulatus Bath, which as mentioned above has a PPi-dependent 6-phosphofructokinase in its CBB cycle. A second PPi-dependent 6-phosphofructokinase with more diverse affiliations is found in the BOGUAY genome only (Fig. S2B). It cannot of course be determined from sequences alone whether one or both are part of the CBB pathway; this enzyme also plays a role in glycolysis (see Section 3.4.1). The BOGUAY genome carries potential genes for both oxidative and reductive TCA
cycles (Table S5), which share a set of reversible reactions and differ at only a few steps. Experimental PLX3397 cell line evidence has been found for the operation of both oxidative and reductive TCA cycles in a single species, depending on growth conditions, for at least one bacterium (Chlorobaculum (Chlorobium) tepidum Tang and Blankenship, 2010) and one archaeon (Thermoproteus tenax Zaparty et al., 2008). Phylogenetic reconstructions based on predicted amino acid sequences suggest a complex evolutionary history for these pathways in the Beggiatoaceae, summarized in Fig. 5 and discussed below. Of the seven reversible steps shared by the two pathways (Fig. 5), four are predicted to be catalyzed by enzymes (AcnB, SucCD, FumAB) that are highly
conserved among the three relatively complete Beggiatoaceae genome sequences available, and one by an enzyme (malate dehydrogenase, Mdh) with close relatives in BOGUAY and B. alba only ( Fig. 6). Beta adrenergic receptor kinase The incomplete BgP genome sequence may or may not encode an Mdh. Most close relatives of these putative proteins are from Gamma- or Betaproteobacteria; only Mdh shows some evidence of more widespread gene exchange, with sequences from several Deinococci among the otherwise gammaproteobacterial neighbors. In contrast, the BOGUAY succinate dehydrogenase (SdhABC; Fig. S4A–C) is most closely related to sequences from the BgP and very incomplete BgS genomes, but is otherwise affiliated with Bacteroidetes sequences and, for SdhC especially, a few species from diverse other groups (e.g., spirochaetes and Ignavibacteria).