Nitrogen-Fixing and Plant Growth-Promoting Ability of Two Endophytic Bacterial Strains Isolated from Sugarcane Stalks

Abstract

Two N2-fixing bacteria isolates, B11S and B8S, were obtained from the surface-sterilized stalks of sugarcane cultivars GT11 and B8. Both isolates showed acetylene reduction activity in nitrogen-free media. The two nitrogen-fixing bacterial isolates produced siderophores, and the ability of B8Ss was higher than that of B11S. The two isolates were also able to dissolve Ca3(PO4)2, and the ability of B11S was higher. It was found that only the strain B8S displayed ACC deaminase activity. The IAA production ability of strain B8S was higher than that of B11S. Both the B11S and B8S isolates were classified on the basis of 16 S rRNA gene sequences and their biological characteristics. The 16 S rRNA gene sequence of isolates B11S and B8S showed 98.5 and 100 % similarities with Stenotrophomonas maltophilia and Agrobacterium tumefaciens (Rhizobium radiobacter), respectively. For both growth and nitrogenase activity of the isolates, the optimum temperature was 31 °C. The optimum pH for their growth was 6.0, but it ranged from 6.5 to 7.0 for nitrogenase activity. The two strains grew faster and showed increased nitrogenase activity with increasing concentration of carbon in the cultural media, for which the sucrose was better compared to glucose. Further, the growth and nitrogenase activity of the strains were found better when cultured in the media containing suitable concentrations of NH4 + and NO3 −; however, the growth of both isolates was hindered significantly with increasing concentration of both nitrogen sources.