Characterization of carotenoids and genes encoding their biosynthetic pathways in Azospirillum brasilense.

Azospirillum brasilense is non-photosynthetic member of the family Rhodospirillaceae. Some strains of this bacterium are reported to produce bacterioruberin-type of carotenoids, which are generally produced by halophilic or psychrophilic bacteria. Since no other member of Rhodospirillaceae produces bacterioruberin-type of carotenoids, we investigated the presence of genes involved in bacterioruberin- and spirilloxanthin- biosynthetic pathway in A. brasilense Cd. Although genes encoding spirilloxanthin pathway were absent, homologs of several genes (crtC and crtF) involved in the biosynthesis of bacterioruberins were present in the genome of A. brasilense Cd. But, the homolog of CruF responsible for the final step in bacterioruberin biosynthesis could not be found. We also characterized the carotenoids of A. brasilense Cd using TLC, HPLC, absorption spectra and HRMS. Resolution of methanol extract of carotenoids in UPLC showed 9 peaks, out of which 6 peaks showed absorption spectra characteristic of carotenoids. HRMS of each peak produced 1-14 fragments with different m/z values. Two of these fragments were identified as 19' Hydroxyfucoxanthinol and 8'Apoalloxanthinal, which are the carotenoids found in aquatic microalgae.