Carbon Dioxide Metabolism and its Regulation in Nonsulfur Purple Photosynthetic Bacteria.

Summary Carbon metabolism in nonsulfur photosynthetic bacteria is a multifaceted subject of study as this large group of bacteria is able to successfully utilize organic as well inorganic carbon, in the form of reduced and oxidized compounds (such as butyrate, malate and succinate) and CO2, respectively, and therefore survive in the most disparate environments. In addition, the process of carbon dioxide assimilation and its regulation have been proven to be essential for maintaining the cellular redox homeostasis. Over the last decade, the molecular mechanisms governing carbon assimilation have been extensively studied in the two representative species, Rhodobacter sphaeroides and Rhodobacter capsulatus, with a detailed analysis of the interaction of the main transcriptional regulator, CbbR, to the promoter regions. The tight physiological link to redox balance has also been elucidated by studying the role of the global regulator redox sensitive two-component system, RegBA, with regard to the expression of the cbb operons. A further level of complexity is present in Rhodopseudomonas palustris, where a unique three-protein two-component system in addition to CbbR is involved in the regulation of CO2 fixation. This chapter will mainly review the progress made in understanding the mechanism of regulation of carbon metabolism in NSP bacteria as well as provide insights on the RubisCO and RubisCO-like enzymes gained from studying the relation structure-function.