9.A.2 The Putative Dissolved Inorganic Carbon Concentrating Transporter (DIC-CT) Family
Many autotrophic microorganisms adapt to scarcity in dissolved inorganic carbon (DIC; = CO2 + HCO3- + CO32-) with CO2 concentrating mechanisms (CCM) which actively transport DIC across the cell membrane to facilitate carbon fixation. The deep-sea vent γ-proteobacterial chemolithoautotroph, Thiomicrospira crunogena, has a low-DIC inducible CCM. Proteins encoded by Tcr_0854 and the adjacent Tcr_0853 genes, required elevated DIC for growth (Mangiapia et al. 2017). Strains carrying mutated copies of Tcr_0853 and Tcr_0854 overexpressed carboxysomes and had diminished ability to accumulate intracellular DIC. Tcr_0853 and Tcr_0854 are cotranscribed and upregulated under low-DIC conditions. The Tcr_0853 protein has 13 - 15 TMSs and is homologous to NADH dehydrogenase subunits (TC#3.D.1). Tcr_0853 and Tcr_0854 may encode a two-subunit DIC transporter. These proteins are widespread among autotrophs from multiple phyla of Bacteria and Archaea. Homologues are present in 14 phyla in Bacteria and in one phylum of Archaea, the Euryarchaeota. Many organisms carrying these homologs are autotrophs, suggesting a role in facilitating dissolved inorganic carbon (Mangiapia et al. 2017).