Physiological Characteristics And Molecular Mechanisms Of Biotite Weathering By Rhizobium Massiliae S41

Mineral weathering is the physical and chemical breakdown of rocks with some ash genisis around them.It occurrs when rocks on the earth's surface or subsurface contact with air,water and organism;Mineral weathering plays an important role in ecology and elements cycle on earth.Bacteria play an important role in mineral weathering and they have different strategies for mineral weathering.It is of great importance to explore how bacteria weather mineral and the molecular mechanisms involved in mineral weathering for illustrating the role of bacteria in silicate mineral weathering.The mineral-weathering bacterium Rhizobium massiliae S41 preserved in our Lab was used to study the physiological characteristics and molecular mechanisms of biotite weathering.The concetrations of Fe,A1 and Si in culture medium are as the indicators of biotite weathering by strain S41.Five genes involved in different pathway of strain S41 were chosen and knocked out via homologous recombination.Biotite weathering by strain S41 and its mutant strains were analyzed.A further study on gene FhuD which can promote biotite weathering of strain S41 was conducted.Strain S41 and S41?FhuD were chosen to weather biotite and potash feldspar.Changes of siderophore production and concentration of intracellular Fe of strain S41 and S41?FhuD were monitered.At last,the expression plasmid of gene FhuD was transformed into strain S41?FhuD.The results indicated that,when there was only glucose or mannose in cultural media,the element(Fe,Al,Si)concentrations were apparently higher than those in cultural media with other carbon sources.The cell numbers,pH value and element concentrations in cultural media containing only(NH4)2SO4 as nitrogen sources were rather lower than those in cultural media containing KNO2,KNO3 or(NH4)2SO4 ?KNO3.When comparing biotite weathering by strain S41 and its mutants,strain S41?FhuD could accelerate the releases of Fe and Si from biotite.Strain S41?FhuD had higher ability to weather biotite containing high Fe than strain S41,while strains S41 and S41AFhuD had similar ability to weather potassium feldspar containing rare Fe,suggesting that the percentage of Fe in mineral might influence the mineral weathering of mutant strain S41?FhuD.The concentration of intercellular Fe of strain S41?FhuD was lower than that of strain S41 at 24 h and 48 h of incubation,therefore the lack of gene FhuD in the bacterium might lead the degeneration of iron-uptake;and strain S41 AFhuD produced more siderophores than that of stain S41 at 24 h and 48 h of incubation,while the synthesis of siderophores was regulated by the Fe concentration in circumstances,indicating the lack of gene FhuD might promote strain S41 to produce much more siderophores.When the whole gene FhuD was transformed into mutant strain S41 AFhuD,it recovered its capacity of biotite-weathering.Strain S41 could grow very well and produce a great amount of exopolysaccharides in cultural media containing glucose or mannose.The deletion of gene FhuD could reduce the iron-uptake efficiency of strain S41,promote strain S41 to produce more siderophores,and accelerate biotite weathering.