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The gammaproteobacterium Thiomicrospira crunogena XCL-2 is an aerobic sulfur-oxidizing hydrothermal vent chemolithoautotroph that has a CO concentrating mechanism (CCM), which generates intracellular dissolved inorganic carbon (DIC) concentrations much higher than extracellular, thereby providing substrate for carbon fixation at sufficient rate. This CCM presumably requires at least one active DIC transporter to generate the elevated intracellular concentrations of DIC measured in this organism. In this study, the half-saturation constant ( K) for purified carboxysomal RubisCO was measured (276 ± 18 µM) which was much greater than the K of whole cells (1.03 µM), highlighting the degree to which the CCM facilitates CO fixation under low CO conditions. To clarify the bioenergetics powering active DIC uptake, cells were incubated in the presence of inhibitors targeting ATP synthesis (DCCD) or proton potential (CCCP). Incubations with each of these inhibitors resulted in diminished intracellular ATP, DIC, and fixed carbon, despite an absence of an inhibitory effect on proton potential in the DCCD-incubated cells. Electron transport complexes NADH dehydrogenase and the bc complex were found to be insensitive to DCCD, suggesting that ATP synthase was the primary target of DCCD. Given the correlation of DIC uptake to the intracellular ATP concentration, the ABC transporter genes were targeted by qRT-PCR, but were not upregulated under low-DIC conditions. As the T. crunogena genome does not include orthologs of any genes encoding known DIC uptake systems, these data suggest that a novel, yet to be identified, ATP- and proton potential-dependent DIC transporter is active in this bacterium. This transporter serves to facilitate growth by T. crunogena and other Thiomicrospiras in the many habitats where they are found. [ABSTRACT FROM AUTHOR]

The interactive effects of inorganic carbon status, temperature and light on chlorosis induced by nitrogen deficiency, and the roles of Clp proteases in this process were investigated. In wild-type cultures grown in high or ambient CO2, following transfer to media lacking combined nitrogen, phycocyanin per cell dropped primarily through dilution of the pigment through cell division, and also suffered variable degrees of net degradation. When grown at high CO2 (5%), chlorophyll (Chl) suffered net degradation to a greater extent than phycocyanin. In marked contrast, growth at ambient CO2 resulted in Chl per cell dropping through dilution. Conditions that drove net Chl degradation in the wild-type resulted in little or no net Chl degradation in aclpPIinactivation mutant, with Chl content dropping largely through growth dilution in the mutant. The chlorotic response of aclpPIIinactivation strain was nearly the same as that of wild-type, although phycocyanin degradation may have been slightly accelerated in the former. [ABSTRACT FROM AUTHOR]