The Diversity Of Culturable Rock-Weathering Bacteria From The Purple Siltstone And The Adjacent Soil And The Mechanisms Involved In Mineral-Weathering

Purple siltstone is a common kind of sedimentary rock.The bacterial communities and the distribution of mineral-weathering bacteria on the rock surfaces and the adjacent soil are still unknown.It is significantly important to evaluate the role of the mineral-weathering bacteria from the rock and the soil on the rock weathering.The research not only enriches the resource of the mineral-weathering bacteria but also provides the basis for illustrating the mechanisms involved in the interaction between bacteria and rocks.Original and weathered purple siltstones and the adjacent soils located in Yanting,Sichuan Province were collected.We used culture method together with the Biolog Eco system to isolate and characterize the bacterial community structure,rock-weathering potential and the carbon source utilization of the culturable bacteria from the rocks and adjacent soils.Two Rhizobium strains were used to compare the mineral weathering pattern and the physiological and biochemical mechanisms.Furthermore,we used wild strain Ensifer adhaerens M78 and its mutants of decreased exopolysaccharides production to characterize the related genes involved in mineral-weathering by the strain.One hundred and fifty culturable bacterial strains were isolated from the purple siltstone and adjacent soil.The strains belonged to 14 genera within five groups(Actinobacteria,Firmicutes,y-Proteobacteria,a-Proteobacteria and Bacteriodetes),among which Arthrobacter,Bacillus,Pseudomonas and Ensifer being the dominant based on the 16S rRN A gene sequence analysis.The genera of Arthrobacter,Bacillus and Ensifer were common in the rock and soil samples.Bacterial strains isolated from original rock belonged to 6 genera within 4 groups,with Leclercia being the specific.Twelve genera were found in the weathered rock and Acinetobacter,Streptomyces,Microbacterium,Novosphingobium and Chitinophaga were specific.Bacterial strains isolated from the soil samples belonged to 6 genera and Enterobacter was unique.In addition,the Biolog analysis indicated that the activity and abundance of culturable microbes were correlated to the rock weathering degree.Moreover,there were significant differences in the metabolic types of the carbon sources by the culturable microbes of the rocks and soil samples.At the same time,the values of S,H',U and AWCD were extremely remarkable positive correlated to the contents of available Fe,Al and organic matter in the rock and soil samples.The mineral-weathering experiment showed the difference in the weathering ability among the bacteria isolated from the different samples.The rock-weathering ability of the bacteria from soil sample was the highest among the three samples.We also found that the 150 strains weathered purple siltstone via producing siderophores and organic acids.Strain H66 was identified based on polyphacis taxonomical methods.The strain is closly related to Rhizobium huautlense S02T(98.1%),Rhizobium alkalisoli CCBAU 01393T(98.0%),Rhizobium cellulosilyticum ALA10B2T(98.0%).The major fatty acids produced by strain H66 are summed feature 8(C18:1?7c and/or C18:1?6c)and C16:0.The DNA G+C content of strain H66 is 60.3 mol%while the values of DNA hybridization are 14.3%?26.4%?27.3%?40.0%?40.0%,respectively.Briefly,strain H66T represents a novel species of the genus Rhizobium,for which the name Rhizobium yantingense sp.nov.is proposed.Two Rhizobiun strains,Rhizobium yantingense H66 isolated from the weathered purple siltstone and Rhizobium etli CFN42 of Rhizobium,were chosen to characterize the mineral weathering pattern and mechanisms in culture media with different nutrition.The results showed that strain H66 had the higher ability to weather potash feldspar than strain CFN42 by increasing the production of organic acids in the culture medium and the cell adsorption on the rock surface.Ensifer adhaerens M78 isolated from the soil sample was found to weather mineral through the production of exopolysaccharides.Based on the exopolysaccharides production by strain M78,we characterize the molecular mechanisms involved in potash feldspar weathering.Transposon insertion was used to screen the mutants which produced less exopolysaccharides than the wild type.The structure of the exopolysaccharides of the wild type and its mutants was detected by FI-IR.At the same time,the genome walking and genome-wide scanning were taken to locate the inserted genes.The results showed that the inserted genes of the mutants were found to be ctrA,yfiH and kspE coding cell cycle response regulator,polyphenol oxidase,capsule polysaccharide ABC transporter permease,respectively.According to the different characters between the mutants and the wild type,we suggest that ctrA,yfiH and kspE may be involved in the mineral-weathering through the process of synthesis and transportation of the exopolysaccharides in different ways.