Role and Function of LitR, an Adenosyl B12-Bound Light-Sensitive Regulator of Bacillus megaterium QM B1551, in Regulation of Carotenoid Production

• Published in: Journal of bacteriology 2015-07, Vol.197 (14), p.2301-2315
• Main Authors: Takano, Hideaki, Mise, Kou, Hagiwara, Kenta, Hirata, Naoya, Watanabe, Shoko, Toriyabe, Minami, Shiratori-Takano, Hatsumi, Ueda, Kenji
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacillus; Bacillus megaterium; Bacillus megaterium - genetics; Bacillus megaterium - metabolism; Bacterial Proteins - metabolism; Base Sequence; Binding Sites; Carotenoids - metabolism; Cobamides - chemistry; Cobamides - metabolism; Deoxyribonuclease I - metabolism; DNA Footprinting; Gene Expression Regulation, Bacterial - physiology; Light; Molecular Sequence Data; Promoter Regions, Genetic; Protein Binding
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/jb.02528-14

The LitR/CarH family of proteins is a light-sensitive MerR family of transcriptional regulators that contain an adenosyl B12 (coenzyme B12 or AdoB12)-binding domain at the C terminus. The genes encoding these proteins are found in phylogenetically diverse bacterial genera; however, the biochemical properties of these proteins from Gram-positive bacteria remain poorly understood. We performed genetic and biochemical analyses of a homolog of the LitR protein from Bacillus megaterium QM B1551, a Gram-positive endospore-forming soil bacterium. Carotenoid production was induced by illumination in this bacterium. In vivo analysis demonstrated that LitR plays a central role in light-inducible carotenoid production and serves as a negative regulator of the light-inducible transcription of crt and litR itself. Biochemical evidence showed that LitR in complex with AdoB12 binds to the promoter regions of litR and the crt operon in a light-sensitive manner. In vitro transcription experiments demonstrated that AdoB12-LitR inhibited the specific transcription of the crt promoter generated by a σ(A)-containing RNA polymerase holoenzyme under dark conditions. Collectively, these data indicate that the AdoB12-LitR complex serves as a photoreceptor with DNA-binding activity in B. megaterium QM B1551 and that its function as a transcriptional repressor is fundamental to the light-induced carotenoid production. Members of the LitR/CarH family are AdoB12-based photosensors involved in light-inducible carotenoid production in nonphototrophic Gram-negative bacteria. Our study revealed that Bacillus LitR in complex with AdoB12 also serves as a transcriptional regulator with a photosensory function, which indicates that the LitR/CarH family is generally involved in the light-inducible carotenoid production of nonphototrophic bacteria.