Responses of Azospirillum brasilense to salinity stress

Abstract

Increase in sodium chloride concentrations inhibited growth, acetylene-reducing activity and indoleacetic acid production in Azospirillum brasilense Cd. Supplementation of glycine betaine did not relieve the salinity stress-mediated inhibition of growth; instead, it added to the growth inhibition. Inhibition of growth of A. brasilense Cd by 2,4-dehydroproline in the presence of 200 mM NaCl suggested the existence of a ProP- or ProU- like transporter which can transport both proline and glycine betaine under osmotic stress. Utilization of glycine betaine as the sole source of nitrogen explained the inability of A. brasilense Cd to use it as an osmoprotectant. Osmoregulatory properties of the two strains of A. brasilense (Sp7 and Cd) suggest that it might be strain-specific.