title: Carotenoid production and phenotypic variation in Azospirillum brasilense.
abstract: We assessed the occurrence of phenotypic variation in Azospirillum brasilense strains Sp7, Cd, Sp245, Az39 and phv2 during growth in rich media, screening for variants altered in colony pigmentation or extracellular polysaccharide (EPS) production. Previous studies showed that EPS-overproducing variants of Sp7 appear frequently following starvation or growth in minimal medium. In contrast, no such variants were detected during growth in rich media in the tested strains except for few variants of phv2. Regarding alteration in colony pigmentation (from pink to white in strain Cd and from white to pink in the others), strain Sp7 showed a relatively high frequency of variation (0.009-0.026%). Strain Cd showed a lower frequency of alteration in pigmentation (0-0.008%), and this type of variation was not detected in the other strains. In A. brasilense, carotenoid synthesis is controlled by two RpoE sigma factors and their cognate ChrR anti-sigma factors, the latter acting as negative regulators of carotenoid synthesis. Here, all tested (n = 28) pink variants of Sp7 carried mutations in one of the anti-sigma factor genes, chrR1. Our findings indicate that, in A. brasilense, phenotypic variation is strain- and environment-dependent and support the central role of ChrR1 in regulation of carotenoid production.
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Electronic address: gal4646@gmail.com.
authors.forename: Gal Reem
authors.initials: GR
authors.lastname: Brenholtz
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Electronic address: dafnata@savion.huji.ac.il.
authors.forename: Dafna
authors.initials: D
authors.lastname: Tamir-Ariel
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Electronic address: yaacov.okon@mail.huji.ac.il.
authors.forename: Yaacov
authors.initials: Y
authors.lastname: Okon
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Electronic address: saul.burdman@mail.huji.ac.il.
authors.forename: Saul
authors.initials: S
authors.lastname: Burdman
mesh_terms: D015806:Azospirillum brasilense / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000096:biosynthesis* / Q000235:genetics; D003470:Culture Media / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D009154:Mutation; D010641:Phenotype; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D011135:Polysaccharides, Bacterial; D012808:Sigma Factor; D002338:Carotenoids
keywords: Anti-sigma factor; Azospirillum; Carotenoids; Extracellular polysaccharides; Phase variation; Phenotypic variation