| In this study,the communities and characteristics of cellulolytic bacteria which isolated from different saline-sodic soil in the Songnen grassland were systematicallystudied and analysis.The isolated cellulolytic bacteria from Leymus chinensis?pH8.68?grassland,Chloris virgata grassland?pH 9.47?and weeds grassland?pH 10.03?were identified by morphological observation,physiological and biochemical tests and 16 S rDNA analysis;the predominant cellulolytic bacteria were determined in different saline sodic soil,and the enzymic and plant growth promoting characteristics of these isolates were studied.The main results of the study are as follows:1.Identification of cellulolytic bacteria from different saline-sodic soilsThe cellulolytic bacteria were analyzed and identified by morphological,biochemical properties and16 S rDNA gene fragment sequences.Our results showed that isolates could grow on the media with pH 7.0-11 and 0-4% NaCl concentrations range.The 16 S rDNA gene fragment sequences were analyzed for 35 cellulolytic bacteria,the same strain was removed,the remaining 27 strains of 16 S rDNA gene fragment sequences were submitted to GenBank,and 27 new strains were sequenced.At the same time,the phylogenetic tree of all strains was constructed on the basis of 16 S rDNA gene fragment sequences analysis.2.Communities analysis of dominant cellulolytic bacteria from different saline-sodic soilsAmong the 27 isolates,10 strains were peculiar in Leymus chinensis grassland soil,9 strains which were peculiar in Chloris virgata grassland soil and 4 strains come from weeds grassland.4 cellulolytic bacteria existed in the two or the three kinds of soil.Streptomyces KY007170.1 and Arthrobacter KY007166.1 were isolated from the Chlorisvirgata grassland and weeds grassland soil simultaneously,Streptomyces KY007169.1 and Arthrobacter KY007185.1 exsisted in three kinds of grassland.It is obviously that these 4 strains have wider distribution and stronger adaptability.The cellulolytic bacteria of three different grassland soils were analyzed by CMC plate,the results showed that among the three kinds of grassland with different salinization degree,the highest abundance of strains were Streptomyces,the abundance were Leymus chinensis?71.4%?,Chloris virgata?71.4%?and Weed grassland?85.7%?.Thus we can concluded that Streptomyces had a strong adapt ability to salinity and alkality,and was dominant group of cellulolytic bacteria in the saline-sodic grassland.3.cellulolyticcharacteristics of isolates(?1?Producing cellulase characteristics by isolatesFirstly,the cellulase activities of the isolates were analyzed by Congo red staining method.Meanwhile,the cellulase activities of the isolates were analyzed by DNS method.The results showed that most of the isolates produced extracellular cellulase,and their enzymatic activities ranged from 1.47 to 6.08×10-2 IU.The cellulase activity of Streptomycessp.DS-22 was the highest,and the activity was 6.08× 10-2IU.?2?Producingxylanase characteristics by isolatesThe xylanase activities of the isolates was analyzed by DNS method.The results showed that most of the isolates produced extracellular xylanase,and their enzymatic activities ranged from 2.23 to 18.80×10-2 IU.The xylanase activity ofMicrobacteriumsp.DS-28 was the highest,and the activity was 18.80×10-2 IU.4.Nitrogen fixation characteristics of isolated strainsThe nitrogen fixing activity of the isolates was observed by using nitrogen free cellulose plate.The result indicatied that these isolates could grow well on the nitrogen free cellulose plate,are a cellulolytic and nitrogen-fixing bacteria.The nitrogenase activity of isolates was determined by acetylene reduction method.Results show that all isolates could produce nitrogenase with the range of 36.29 to 112.08 nmol.ml.h-1.The nitrogenase activity ofStreptomyce sp.DS-18 was the highest,and the activity was 112.08×10-2 IU.5.Plant growth promoting characteristics of isolated strainsThe ability of producing IAA,siderophore,phosphate solubilizing ability and antibacterial activity of isolate strains were detected.The results showed that all strains could produce IAA?range from 2.4 to 80.69mg/L?and Bacillus sp.DS-34 produced the maximum content of IAA.6Streptomyces strains had the ability of siderophore production.8 strains?7Streptomyces and 1Bacillus?had phosphate solubilizing ability.11 strains had the antibacterial ability,including 7Streptomyces,2Arthrobacter,1Nocardia and 1Flavobacterium.6.Physical and chemical properties and biomass analysis of different saline-sodic soilsThe physical and chemical characteristics and biomass of different saline-sodic soils were analyzed,the results showed the content of total nitrogen and organic carbon decreased with the increase of soil salinity.With the increase of soil salinity and pH,the biomasses in soil were: bacteria>actinomycetes>cellulolytic bacteria>fungus.7.Plant growth promoting experiment of isolated strainsThree strains of Streptomyces sp.DS-22,DS-2 and DS-30 with high enzymic activity were selected to study the growth promoting effect on Leymus chinensis.Pot experiment showed that the plant growth promoting effect of the one strain group of was significantly higher than the control group,and the plant growth promoting effect of mixed strains was more obvious than one strain group.These results suggested that the cellulolytic bacteria from the saline-sodic soil had the growth promoting effect to Leymus chinensis. |
PDF Full Text Request