The Weathering Of Slate In The Presence Of Rock-weathering Bacteria And The Mechanisms Involved

Slate is a transitional metamorphic rock from mud shale to metamorphic rock,which is one of the main components of the shallow crust of the earth and widely distributed in China.The weathering of microorganisms on rocks(minerals)is one of the most important geochemical phenomena occurring on the surface and nearby,which promotes the formation of sediments,soil and topography,and determines the fertility of soil and quality of water,and also has important influence on the formation and development of geologic hazard.We study the effect and mechanism of rock weathering bacteria on slate weathering for providing the experimental basis for deeply understanding of slate-bacteria interaction.In this study,two strains(E153 and F74)with high weathering ability were screened from the twenty-three bacterial strains by physiological and biochemical analysis of the strains and rock weathering test.The weathering characteristics of slate in the presence of the strains were studied under different culture conditions.The results showed that Pantoea sp.E153 and Arthrobacter sp.F74 had tolerance to the concentration of NaCl(0%?3%),pH(4.0?8.5)and temperature(18??45?).The two strains had significantly different ability to release Fe,Si,Ca and Al.Under different carbon and nitrogen sources,strains E153 and F74 had the best effect on the release of elements(Fe,Si,Ca and Al)from the rock when the carbon and nitrogen sources were glucose and(NH4)2SO4 respectively.Under different glucose content(2 g L-1,4 g L-1),NaCl concentration(0%,1%,3%)and temperature(15?,30?),releases of Fe,Si Ca and Al from slate in the presence of strain E153 were significantly higher than in the presence of strain F74.The pH and cell numbers in the culture medium with strain E153 were lower than with strain F74 and strain E153 produced higher gluconic acid content in the culture medium than strain F74.During three months of incubation under standing condition,strain E153 had higher ability to release Fe and Al than strain F74 at the first ten days,then strain E153 had lower ability to release Fe and Al than strain F74 ten days later,which showed that soluble Fe and Al in the culture medium might be changed to insoluble Fe and Al compounds in the later stage of the experiment in the presence of strain E153.Furthermore,strain E153 had higher ability to release Si,Ca and produce gluconic acid than strain F74.Scanning electron microscopy revealed that cells of the strains were present on the surfaces of the slate for the first 30 days of inoculation.After 70th and 90th days of incubation,the micro-mineral particles(<5 ?m)were obtained in the presence of the strains but not in the absence of the strains.X-ray diffraction analysis showed that the composition of the micro-mineral particles was consisted of quartz,mica,kaolinite and a small amount of clay minerals.In addition,strains E153 and F74 could accelerate the rock weathering process by producing gluconic acid and both strains could promote slate fragment in a short time.