A Nitrogen-Fixing Bacterium Paenibacillus sp. GD812 Antagonistic Against Plant Pathogenic Fungi

【Objective】 The objective of this study is to screen nitrogen-fixing bacteria antagonistic against plant pathogenic fungi and research nitrogenase activity,nifH,physiological and biochemical characteristics,identification,stress resistance of the functional strains and inoculation effect on plant and to prepare strains for microbial fertilizer production.【Method】 Nitrogen-free medium was used to isolate nitrogen-fixers and confrontation method was used to screen antagonistic bacteria against plant pathogenic fungus.Nitrogenase activity was determined with acetylene reduction assay.16S rDNA and nifH were amplified with PCR.Strain identification was carried out based on the morphology,physiology,and biochemical test and 16S rDNA sequence analysis.Microbial inoculation effect on plant was tested with a pot culture in green house.【Result】 One strain designated as GD812 was selected,which showed nitrogenase activity 30.661 nmol C2H4/h?mg protein,and strongly antagonistic against plant pathogenic fungi Gibberella zeae and Verticillium dahliae with the inhibition rate of 59.5% and 49.3%,respectively.nifH of GD812 is 300 bp sharing 98% sequence identity with that of Paenibacillus sp.Bs57.GD812 was identified as Paenibacillus sp.based on the results of morphology,physiology and biochemical test and 16S rDNA sequence analysis.Further investigations showed that GD812 could use 20 of the 35 tested carbon sources,could grow under temperature ranging from 4 to 50℃,and could grow in range of pH4 to11.Pot culture result showed that fresh weight of Chinese cabbage inoculated with GD812 increased by 52% compared with the control.【Conclusion】 The newly selected Paenibacillus sp.GD812 showed high nitrogenase activity,strong antagonism against plant pathogenic fungi,extensive carbon source utilization,stress resistance and good inoculation effect,which is a candidate to be further developed for microbial fertilizer production.