%0 Journal Article %A Thirunavukkarasu, Nagarajan %A Mishra, Mukti Nath %A Spaepen, Stijn %A Vanderleyden, Jos %A Gross, Carol A. %A Tripathi, Anil K. %T An extra-cytoplasmic function sigma factor and anti-sigma factor control carotenoid biosynthesis in Azospirillum brasilense %D 2008 %J Microbiology, %V 154 %N 7 %P 2096-2105 %@ 1465-2080 %R https://doi.org/10.1099/mic.0.2008/016428-0 %K ECF, extra-cytoplasmic function %I Microbiology Society, %X Strains Sp7 and Cd of Azospirillum brasilense, a plant growth-promoting rhizobacterium, differ in synthesis of carotenoids. While colonies of strain Sp7 have a white–cream colour on plates, colonies of strain Cd are orange–pink coloured because of the synthesis of carotenoids. Screening of a mini-Tn5 mutant library of A. brasilense Sp7 revealed two orange–pink-coloured mutants that produced carotenoids. Cloning and sequencing of the Tn5 flanking region in both the carotenoid-producing mutants of Sp7 revealed insertion of Tn5 in an ORF encoding anti-σ factor, a ChrR-like protein. The upstream region of the Tn5-mutated ORF contained another ORF that encoded an extra-cytoplasmic function (ECF)-class σ factor (σ E, RpoE). When the nucleotide sequences of the corresponding ORFs from the carotenoid-producing strain Cd were analysed, the sequence of the Cd σ E was identical to that of the carotenoid non-producing strain Sp7, but the Cd anti-σ E ORF had a deletion that caused frame shifting and creation of a stop codon. This resulted in the premature termination of the protein, which was about 7 kDa smaller than the Sp7 anti-σ E. Cloning of Sp7 anti-σ E in a broad-host-range expression vector and expression in A. brasilense Cd and in the anti-σ E knockout mutant of A. brasilense Sp7 resulted in the inhibition of carotenoid synthesis. Similarly, cloning and overexpression of A. brasilense Sp7 σ E in A. brasilense Sp7 resulted in the production of carotenoids. These observations clearly indicate that carotenoid synthesis in A. brasilense is controlled by σ E with its cognate anti-σ E. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.2008/016428-0