Research On Characteristics Of Nitrogen-Fixing Microorganisms In Alkali-Saline Grassland Soil

A large number of nitrogen-fixing bacterias exist independently in the saline-sodic soils,the role of these bacterias in the nitrogen cycle of soil has been widespread concerned.Ten azotobacters were isolated from soil sample which came from the surface of the Leymus chinensis litter in songnen grassland by improved Ashby nitrogen-free medium plate in this study.We identified these strains by morphological analysis,physiological and biochemical reactions and 16 SrDNA sequence analysis,researched the activity of nitrogenase or others,growth-promoting characteristics and promoting effect for Leymus chinensis of these strains.The results of the study are as follows:1.The morphological biochemical characteristics,as well as sequences of 16 S rDNA of the isolates were analyzed.The isolates preliminarily were identified as four strains of Streptomyces,two strains of Pseudomonas,one strain of Gordonia terrae,one strain of Acinetobacter lwoffii,one strain of Mycobacterium neoaurum,one strain of Agrobacterium tumefaciens.Genbank nucleic acid sequence accession numbers of 10 isolates strains were logined KJ716539,KJ742897-KJ742905.All strains were resistance to salt,and grew well in medium with 4% NaCl and pH 10.5;hydrogen sulfide test,catalase test were positive;most of strains were positive in gelatin liquefaction test,starch hydrolysis test,sugar fermentation test,several strains were positive in methyl red test.All strains can grew well when maltose,sodium carboxymethylcellulose,sucrose,mannitol,dextrin,lactose,starch,xylose,citrate act as the carbon source.2.Nitrogenase activity of isolated strains was studied,using acetylene reduction method to determined amounts of produced ethylene through gas chromatograph proved that all the strains had activity of nitrogenase,and activity ranged from2.21 nmol C2H4 h-1mL-1 to 4.44 C2H4 h-1mL-1.3.CMCase activity of isolates was reseached,we measured production of reducing sugar through dinitrosalicylic acid method with CMC and straw as substrates.The experimental results showed that Sn-12,Sn-21,Sn-22,Sn-23,Sn-26 had cellulose hydrolysis activity which significantly higher when straw as a substrate than CMC as substrate.4.Xylanase producing activity of isolates were measured by DNS method.All the isolates produced xylanase,and the strains Sn-23 and Sn-26 have higher xylanase activities.5.Growth-promoting properties of isolates were studied,the experimental results showed that Sn-19,Sn-20 and Sn-23 had the ability to dissolve phosphorus;all strains produced IAA and Sn-23 has highest yield;the result of bacterial antibacterial activity test showed that Sn-15,Sn-18,Sn-21,Sn-23 and Sn-26 acted significantly antibacterial effect when Staphylococcus aureus as the indicator strain,especially Sn-18;Sn-15,Sn-22,Sn-23 strain have obvious antibacterial effect when E.coli as the indicator strain,and the inhibitory effect of Sn-22 was best.6.Growth-promoting characteristics of isolates to Leymus chinensis were studied,pot experiments of Leymus chinensis with mountain soil and saline soil were imposed Sn-5 and exogenous alkaline bacteria.The result showed that exogenous alkaline bacteria performed higher promoting effect under the condition of pH = 9,100 mmol [Na +] for Leymus Chinensis than Sn-5;two experimental groups of Sn-5 and exogenous alkaline bacteria had higher promoting effect than the control group in pot experiment of leymus chinensis.