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Putative dissolved inorganic carbon concentrating transporter, Tcr_0853/Tcr_0854, of 823 and 0 TMSs and 518 aas and 13 - 15 TMSs, respectively (Mangiapia et al. 2017). Tcr_0853 is an NADH-ubiquinone oxidoreductase chain 5 homologue.

Tcr_0853/Tcr_0854 of Thiomicrospira crunogena

DabB2/DabA2 putative CO2 concentrating transporter, where DabB2 is a possible inorganic ion (H+ or Na+) transporter, homologous to integral membrane NADH dehydrogenase subunits, while DabA2 is homologous to carbonic anhydrases.  Bacterial autotrophs often rely on CO2 concentrating mechanisms (CCMs) to assimilate carbon. Desmarais et al. 2019 performed a genome-wide barcoded transposon screen to identify essential and CCM-related genes in the γ-proteobacterium Halothiobacillus neapolitanus. Screening revealed that the CCM comprises at least 17 and probably no more than 25 genes, most of which are encoded in 3 operons. Two of these operons (DAB1 and DAB2) contain a two-gene locus that encodes a domain of unknown function (Pfam: PF10070) and a putative cation transporter (Pfam: PF00361). Physiological and biochemical assays demonstrated that these proteins (named DabA and DabB for "DABs accumulate bicarbonate") - assemble into a heterodimeric complex that contains a putative β-carbonic anhydrase-like active site and functions as an energy-coupled inorganic carbon (Ci) pump. DAB operons are found in a diverse range of bacteria and archaea. Desmarais et al. 2019 demonstrated that functional DABs are present in the human pathogens, Bacillus anthracis and Vibrio cholerae. They proposed that DABs constitute a class of energized Ci pumps and play a critical role in the metabolism of Ci throughout prokaryotic phyla. Since the uptake of Ci is inhibited by the ionophore CCCP, DAB2 activity may be energetically coupled to a cation gradient, and as DabA2–DabB2 shows pH-independent rescue of carbonic anhydrase-free E. coli, CO2 is probably the transported substrate. Holthuijzen et al 1987 (DOI 10.1007/BF00463489) reported similar findings for Halothiobacillus neapolitanus, and (Menning et al. 2016) got similar results for Hydrogenovibrio crunogenus (Thiomicrospira crunogena). Both DAB operons in Halothiobacillus are required; each having an HCR phenotype when knocked out. A double deletion, which might be expected to have a more severe phenotype, was not constructed.

DabB2/DabA2 of Halothiobacillus neapolitanus (Thiobacillus neapolitanus)

Putative inorganic carbon, Ci, concentrating system with two components, BaDabB and BaDabA (Desmarais et al. 2019).

Terrabacteria group
DabBA of Bacillus anthracis