biostudies-literatureTeikari JEAcademy of FinlandAcademy of Finland (Suomen Akatemia)Deutsche ForschungsgemeinschaftDeutsche Forschungsgemeinschaft (German Research Foundation)42https://www.ebi.ac.uk/biostudies/studies/S-EPMC11890772biostudies-literatureUnknown11(1)Cyanobacteria of the Nostoc genus are capable of forming symbiotic relationships with plants but also serve as a hub for heterotrophic bacteria. By comparing the axenic strain Nostoc punctiforme PCC 73102 and the xenic strains Nostoc sp. KVJ2 and KVJ3, we were able to demonstrate an almost obligate dependence of the cyanobacteria on the heterotrophic partners under carbon-limiting conditions. A detailed analysis of the intimate relationship between N. punctiforme and the isolate Agrobacterium tumefaciens Het4 using shotgun proteomics and microscopy uncovered a complex partnership characterized by competition for iron and facilitation for carbon. The prevalent extracarboxysomal localization of the carbon-fixing enzyme RubisCO suggests that a weak carbon-concentrating mechanism in N. punctifNPJ biofilms and microbiomesCompetition and interdependence define interactions of Nostoc sp. and Agrobacterium sp. under inorganic carbon limitation.PMC11890772239748522- SFB 1127406260942332215Heuser MBaumann OLiaimer AZedler JAZDittmann ETeikari JERusso DAfalseCompetition and interdependence define interactions of Nostoc sp. and Agrobacterium sp. under inorganic carbon limitation.Cyanobacteria of the Nostoc genus are capable of forming symbiotic relationships with plants but also serve as a hub for heterotrophic bacteria. By comparing the axenic strain Nostoc punctiforme PCC 73102 and the xenic strains Nostoc sp. KVJ2 and KVJ3, we were able to demonstrate an almost obligate dependence of the cyanobacteria on the heterotrophic partners under carbon-limiting conditions. A detailed analysis of the intimate relationship between N. punctiforme and the isolate Agrobacterium tumefaciens Het4 using shotgun proteomics and microscopy uncovered a complex partnership characterized by competition for iron and facilitation for carbon. The prevalent extracarboxysomal localization of the carbon-fixing enzyme RubisCO suggests that a weak carbon-concentrating mechanism in N. punctif2025-01-01T00:00:00Z2025 Mar2026-07-15T08:52:46.459Z2025-04-06T08:35:04.158ZS-EPMC118907724005753910.1038/s41522-025-00675-0