Screening And Identification Of Extracellular Polysaccharide Producing Strains From Shapotou Ningxia And Their Growth Charcteristics

Biological soil crust is a Kind of special desert landscape that is the result of the interaction between biological and soil.Bacterium itself and its metabolites in,especially extracellular polysaccharide,changed the microstructure of the soil,enriched the soil organic matter,increased the stability of soil,and played an important role in the way of windbreak and sand-fixation.Hence we need to isolate and identify the strains of exopolysaccharide production from the arid biological soil crust as well as study their growth characteristics of environmental adaptation in order to further study the role of microorganisms in the aspect of sand-fixation.In this study we measured physical and chemical properties of artificial biological crust from Desert Experimental Station in Ningxia Shapotou and natural biological crust,including the mechanical composition of the soil,organic matter content,total nitrogen content and soil pH,using the method of particle separation method,potassium dichromate oxidation reduction method and kjeldahl determination and potential method,respectively.And then the strains of exopolysaccharide production were isolated from artificial biological crust and natural biological crust using the plate dilution method;and do a quantitative analysis for these strains with phenol-sulfuric acid method,furthermore identify them on the basis of morphological characteristics of the strains,physiological biochemical characteristics and 16 S rRNA gene sequence homology analysis results.The effects of different temperature,pH and salinity on the growth of extracellular polysaccharide production strains were studied.There are the results as follows:1.artificial biological crust and natural biological crust were mainly composed of coarse sand(0.25-0.5mm)and fine sand(0.1-0.25mm)composition,and compared with ordinary soil,organic matter content and total nitrogen content were relatively low,they are alkaline soil due to the determination of soil pH value greater than 8.2.The isolated strains were 15 and 17 from the artificial biological crust and the natural biological crust respectively.3.5 strains from the artificial biological crust and 3 strains from natural biological crust were all secrete extracellular polysaccharide,which the polysaccharide yield of SPT-W1 was highest and reached 26.286 ?g / m L at 48 h.The polysaccharide secreted of SPT-J7 can reach 24.857 ?g / m L at 36 h that is close to SPT-W1.4.SPT-W1,SPT-W2,SPT-W4,SPT-W8 and SPT-W14 were identified as Bacillus and SPT-J7 is identified as Arthrobacter as well as SPT-J13 and SPT-J17 is Microbacterium according to their morphological,physiological and biochemical test results and 16 S rRNA sequence homology analysis.5.The 8 strains can all grow well in the temperature range of 20~40?,p H range of 6.0~9.0 and salinity under 4%,which SPT-W1 is a strain of high temperature resistant and saline-alkaline tolerance that the optimum growth temperature and the optimum pH was 40? and 9.0,respectively,and can grow under the condition of 11% of NaCl.