Surface Adhesion Of Pseudomonas Azotoformans F77 On Biotite Promotes Mineral Weathering And The Mechanisms Involved

Mineral weathering is of great significance for soil formation,soil fertility and environmental protection.The process of mineral weathering is complex and microorganisms are the main players.There are many reports on the mechanisms of bacteria weathering minerals.However,there is little reports about the impact of surface adhesion on mineral weathering by microorganisms.Studying the adhesion of bacteria on mineral surface can better understand the mechanism of bacterial mineral weathering,and it is of great significance to fully understand the role of bacteria in the weathering process of silicate minerals.In this study,four mineral-weathering bacteria F77,M68,M78 and E153 were used as test strains,and their biological characteristics related to mineral weathering were preliminarily determined.The concentrations of Fe,Al and Si elements in the fermentation broth were used as the weathering index to compare the ability of the four bacteria to weather biotite.The result showed that strain F77 was better in mineral weathering than the other three strains.The concentrations of Fe,Al and Si released were up to 32.2 uM,29.3 uM and 138 uM in the presence of strain F77,which were 1.1-4.2,1.2-5.0 and 1.2?2.4-fold than those in the presence of strains M68,M78 and E153.Strain F77 was used to explore the mechanisms involved in biotite weathering.Dialysis bag experiment was used to separate bacteria and biotite to explore the effect of adhension by strain F77 on biotite weathering.The 15 d of shake flask test and static test results showed that mineral weathering by strain F77 may be related to the production of gluconic acid,extracellular polysaccharides and adhension of strain F77 on the surface of biotite.Under standing culture conditions,when strain F77 contacted with biotite directly,the concentrations of dissolved Fe and Al were 1.3-2.5-fold and 1.2-1.6-fold than those under no directly contact with biotite.Under dynamic culture conditions,when strain F77 contacted with biotite directly,the concentrations of dissolved Fe and Al were 1.2-2.3-fold,1.3?1.6-fold than those under no directly contact with biotite.Combining with whole genome and transcriptome of strain F77,we analyzed the genes that may be related to mineral weathering.Three pilus genes(fimA,ecpD,pil0)and a pilus adhesin gene(orf01147)associated with adhesion capacity were selected and knocked out via homologous recombination.The ability of the mutant and wild strains were compared for their mineral weathering.The results showed that the mineral-weathering ability of strain F77?fimA and F77AecpD was the same to the wild strain.Compared with the wild strain,the concentrations of dissolved Fe and A1 in the presence of strain F77?pilO decreased 10?20%and 12?15%at the first three days,and there was no significant difference in the dissolved Fe and A1 concentrations at later period.The concentrations of dissolved Fe and A1 in the presence of strain F77Aorf01147 decreased 11?24%and 12?18%compared to the wild strain.Strain F77?orf01147 which showed significantly decreased mineral weathering ability was further analyzed.The amount of exopolysaccharide produced by F77?orf01147 was reduced by 12.8?32.4%and the adhesion of the mutant strain on the surface of biotite were significantly lower than the wild strain.At last,the expression plasmid of gene orf01147 was transformed into strain F77?orf01147.The result showed that when the deletion gene orf01147 were complemented into strain F77?orf01147,similar mineral weathering ability was observed between the complement and wild strains.