biostudies-literatureMacCready JSDivision of Molecular and Cellular Biosciences277-297https://www.ebi.ac.uk/biostudies/studies/S-EPMC8359340biostudies-literatureUnknown116(1)Carboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is used to equally space out β-carboxysomes across cell lengths by a two-component system (McdAB) in the model cyanobacterium Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among β-cyanobacteria, which possess β-carboxysomes, but are absent in α-cyanobacteria, which possess structurally and phyletically distinct α-carboxysomes. Cyanobacterial α-carboxysomes are thought to have arisen in proteobacteria and then horizontally transferred into cyanobacteria, which suggests that α-carboxysomes in proteobacteria may also lack the McdAB system. Here, using the model chemoautotrophic proteobaMolecular microbiologyThe McdAB system positions α-carboxysomes in proteobacteria.PMC835934018174781941966Vecchiarelli AGBasalla JLMacCready JSTran LHakim PfalseThe McdAB system positions α-carboxysomes in proteobacteria.Carboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is used to equally space out β-carboxysomes across cell lengths by a two-component system (McdAB) in the model cyanobacterium Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among β-cyanobacteria, which possess β-carboxysomes, but are absent in α-cyanobacteria, which possess structurally and phyletically distinct α-carboxysomes. Cyanobacterial α-carboxysomes are thought to have arisen in proteobacteria and then horizontally transferred into cyanobacteria, which suggests that α-carboxysomes in proteobacteria may also lack the McdAB system. Here, using the model chemoautotrophic proteoba2021-01-01T00:00:00Z2021 Jul2026-05-08T20:22:32.912Z2022-02-11T08:27:37.338ZS-EPMC83593403363821510.1111/mmi.14708