Identification and Efficiency of a Nitrogen-fixing Endophytic Actinobacterial Strain from Sugarcane

Sugarcane production in China mostly uses a high amount of chemical nitrogen (N) as compared to the average use of other countries. A microbe-based alternative may help to manage this problem in ecofriendly manner. Therefore, the present study focused on the characterization of a sugarcane growth-promoting nitrogen-fixing endophytic actinobacteria. The actinobacterial strain WZS021 was identified on the basis of morphology, biology and sequencing of 16S rRNA, gyrB and acdS gene amplification. The nitrogenase activity was determined with acetylene reduction assay and effects of different nutritional conditions were evaluated, and 15N isotope dilution method was used to determine the N-fixing capability under sugarcane seedlings in the pot. The strain was identified as Streptomyces chartreusis, by three genes (16S rRNA, gyrB and acdS), but nifH gene showed similarity with Bacillus and these results showed nitrogen fixation ability and 1-aminocyclopropane-1-carboxylate deaminase enzyme production ability at the molecular level. Moreover, strain WZS021 showed maximum nitrogenase enzyme production under pH 8 and sustained at higher temperature. Different carbon sources have less influence on nitrogenase activity. However, small amounts of N source can stimulate the nitrogenase activity, but after certain concentration it starts to inhibit the enzyme activity. Next to this, in the 15N isotope pot assay strain WZS021 significantly enhanced the dry weight of shoot and root by 20 and 75%, and N content increased by 30 and 36%, respectively. The N-fixation percentage of strain WZS021 under sugarcane seedlings was 9.16%. Overall, N-fixing ability of Streptomyces chartreusis strain WZS021 was characterized, and sugarcane biomass enhancement and substantial %Ndfa indicated that the promising strain could be applied in sugarcane as a growth promoter.