Role of Choline and Glycine Betaine in Azospirillum brasilense Cd Under Salinity Stress

Abstract

Glycine betaine has been reported to act as osmoprotectant in Azospirillum brasilense Sp7 but choline failed to produce a similar effect. A plasmid (pFF600) containing betABT operon of E. coli on a broad host range vector was conjugatively mobilized into A. brasilense Cd. The transconjugants failed to use choline as osmoprotectant. The comparison of growth and acetylene reducing activity of parent and transconjugant revealed that neither choline nor glycine betaine acted as osmoprotectant. Acetylene reducing activity was proportionally inhibited with increasing salinity stress. Glycine betaine but not choline inhibited the growth completely at 20mM concentration in the absence of salinity stress. Analysis of 35S-methionine labeled proteins after salinity upshock revealed the inhibition of at least four proteins and induction/enhancement of about six proteins. The protein profile revealed a ca. 31 kDa protein which was induced under salinity stress but was inhibited by glycine betaine. Western blotting of total and periplasmic proteins and immunological detection with anti-glycine betaine binding protein antibody of E.coli revealed cross reaction with a 31 kDa protein and also with a protein of 18 kDa. The 31 kDa cross reacting band was present with or without salinity stress with or without choline or glycine betaine. These observations suggest that osmoregulation in A. brasilense Cd differs from A. brasilense Sp7.