Thiomicrorhabdus heinhorstiae sp. nov. and Thiomicrorhabdus cannonii sp. nov.: novel sulphur-oxidizing chemolithoautotrophs isolated from the chemocline of Hospital Hole, an anchialine sinkhole in Spring Hill, Florida, USA.

Two sulphur-oxidizing, chemolithoautotrophic aerobes were isolated from the chemocline of an anchialine sinkhole located within the Weeki Wachee River of Florida. Gram-stain-negative cells of both strains were motile, chemotactic rods. Phylogenetic analysis of the 16S rRNA gene and predicted amino acid sequences of ribosomal proteins, average nucleotide identities, and alignment fractions suggest the strains HH1T and HH3T represent novel species belonging to the genus Thiomicrorhabdus. The genome G+C fraction of HH1T is 47.8 mol% with a genome length of 2.61 Mb, whereas HH3T has a G+C fraction of 52.4 mol% and 2.49 Mb genome length. Major fatty acids of the two strains included C16 : 1, C18 : 1 and C16 : 0, with the addition of C10:0 3-OH in HH1T and C12 : 0 in HH3T. Chemolithoautotrophic growth of both strains was supported by elemental sulphur, sulphide, tetrathionate, and thiosulphate, and HH1T was also able to use molecular hydrogen. Neither strain was capable of heterotrophic growth or use of nitrate as a terminal electron acceptor. Strain HH1T grew from pH 6.5 to 8.5, with an optimum of pH 7.4, whereas strain HH3T grew from pH 6 to 8 with an optimum of pH 7.5. Growth was observed between 15-35 °C with optima of 32.8 °C for HH1T and 32 °C for HH3T. HH1T grew in media with [NaCl] 80-689 mM, with an optimum of 400 mM, while HH3T grew at 80-517 mM, with an optimum of 80 mM. The name Thiomicrorhabdus heinhorstiae sp. nov. is proposed, and the type strain is HH1T (=DSM 111584T=ATCC TSD-240T). The name Thiomicrorhabdus cannonii sp. nov is proposed, and the type strain is HH3T (=DSM 111593T=ATCC TSD-241T).

Dissolved Inorganic Carbon-Accumulating Complexes from Autotrophic Bacteria from Extreme Environments.

In nature, concentrations of dissolved inorganic carbon (DIC; CO2 + HCO3- + CO32-) can be low, and autotrophic organisms adapt with a variety of mechanisms to elevate intracellular DIC concentrations to enhance CO2 fixation. Such mechanisms have been well studied in Cyanobacteria, but much remains to be learned about their activity in other phyla. Novel multisubunit membrane-spanning complexes capable of elevating intracellular DIC were recently described in three species of bacteria. Homologs of these complexes are distributed among 17 phyla in Bacteria and Archaea and are predicted to consist of one, two, or three subunits. To determine whether DIC accumulation is a shared feature of these diverse complexes, seven of them, representative of organisms from four phyla, from a variety of habitats, and with three different subunit configurations, were chosen for study. A high-CO2-requiring, carbonic anhydrase-deficient (ΔyadF ΔcynT) strain of Escherichia coli Lemo21(DE3), which could be rescued via elevated intracellular DIC concentrations, was created for heterologous expression and characterization of the complexes. Expression of all seven complexes rescued the ability of E. coli Lemo21(DE3) ΔyadF ΔcynT to grow under low-CO2 conditions, and six of the seven generated measurably elevated intracellular DIC concentrations when their expression was induced. For complexes consisting of two or three subunits, all subunits were necessary for DIC accumulation. Isotopic disequilibrium experiments clarified that CO2 was the substrate for these complexes. In addition, the presence of an ionophore prevented the accumulation of intracellular DIC, suggesting that these complexes may couple proton potential to DIC accumulation. IMPORTANCE To facilitate the synthesis of biomass from CO2, autotrophic organisms use a variety of mechanisms to increase intracellular DIC concentrations. A novel type of multisubunit complex has recently been described, which has been shown to generate measurably elevated intracellular DIC concentrations in three species of bacteria, raising the question of whether these complexes share this capability across the 17 phyla of Bacteria and Archaea where they are found. This study shows that DIC accumulation is a trait shared by complexes with various subunit structures, from organisms with diverse physiologies and taxonomies, suggesting that this trait is universal among them. Successful expression in E. coli suggests the possibility of their expression in engineered organisms synthesizing compounds of industrial importance from CO2.