Diversityand Cadmium Tolerance Of Endophytic Bacteria Isolated From Oryza Officinalis In Wuzhou

Endophytic bacteria has been wildly researched due to it's character to promote plant growth and asisste host plant to tolerant stress or bio-stress.The main researches include novel species mining,microbial fertilizer application and new drug research and development and so on.However,cadmium pollution is increasingly serious,which seriously affects the daily life of people and production of mankind.To explore the diversity of endophytic bacteria in wild rice and the tolerance of endophytic bacteria to heavy metal cadmium stress,to reduce cadmium content in polluted water by utilizing cadmium-resistant endophytic bacteria,which all have gradually become the current environmental management focus points.In this research,Oryza officinalis sampled from Wuzhou of Guangxi were used as experimental material,and varieties of culture medium were used to separate and purify the endophytic bacteria.Random insert sequence fingerprinting patern?IS-PCR fingerprint?were used toclusterthe isolated endophytic bacteria.And then,16S rRN A gene sequences were obtained to construct systematical phylogenetic tree,which were used for phylogenetic analysis.The experiment of physiological and biochemical tests were used to screen out some strongly growth-promoting endophytic bacteria,and screen out some cadmium tolerant bacteria to analyze their ability to reduce Cd content on liquid sample.Two strains of endophytic bacteria with cadmium-resistant growth which were obtained by screening cadmium resistance from 19 strains are Kosakonia sacchari HS233 and Bacillus cerus Y10.They have a strong salt tolerance and can utilize varieties of carbon sources for their growth nutrition.In addition,they also can grow at a wide range of p H condition.Carbon source that can be used by Kosakonia sacchari HS233is more abundant thanthe carbon source used by Bacillus cerus Y10.Kosakonia sacchari HS233has a better effect of broad-spectrum antibiotics.Kosakonia sacchari HS233 couldmake the content of cadmium masked by it reach 99.86%,93.24%and 91.81%at concentrations of 100?M,200?M and400?M of cadmium solution.Under the same circumstances,Bacillus cerus Y10couldmake the content of cadmium masked by it reach 99.78%?79.44%?52.29%.The extracellular thiol-containing protein content synthesized by Kosakonia sacchari HS233was 3.16 times higher than that of the control group,but the intracellular thiol-containing protein content did not change significantly after treatment with a cadmium solution at a concentration of 500?M.The intracellular thiol-containing protein content synthesized by Bacillus cerus Y10 was 11.22 times that of the blank group,but the extracellular thiol-containing protein content synthesized by both of them is not much different.However,although the content of thiol-containing protein secreted by Bacillus cerus Y10 is relatively low,the extracellular protein or small molecules secreted by it can combine with Cd²⁺to make the Cd²⁺lose its effect.The results of determination of mercapto content and the determination of cadmium content were consiste nt,which indicated the two strains can absorb a lot of Cd²⁺and secret some extracellular product like thiol-containing protein in different concentrations of cadmium solution.At the same time,it showed that the higher cadmium concentration,the smaller ability of microorganisms to adsorb cadmium.Therefore,in practical application,additional carbon source can be added to promote the bacteria growth and make them absorb a large amount of cadmium,or make the bacteria into biological sludge to deal with the sewagerepeatedly.In the other hand,we can apply the bacteria to the soil and make it into microbial fertilizer.Those bacteria can secret some extracellular product and release them to the soil.Simultaneously the soil has the function of a filter so that reduce the cadmium content around the plant roots.