Banfield,J.F., Barker,W.W., Welch,S.A. and Taunton,A.(1999): Biological impact on mineral dissolution: Application of the lichen model to understanding mineral weathering in the rhizosphere. Proc. Natl. Acad. Sci. USA, 96, 3404-3411.


 Microorganisms modify rates and mechanisms of chemical and physical weathering and clay growth, thus playing fundamental roles in soil and sediment formation. Because processes in soils are inherently complex and difficult to study, we employ a model based on the lichen-mineral system to identify the fundamental interactions. Fixed carbon released by the photosynthetic symbiont stimulates growth of fungi and other microorganisms. These microorganisms directly or indirectly induce mineral disaggregation, hydration, dissolution, and secondary mineral formation. Model polysaccharides were used to investigate direct mediation of mineral surface reactions by extracellular polymers. Polysaccharides can suppress or enhance rates of chemical weathering by up to three orders of magnitude, depending on the pH, mineral surface structure and composition, and organic functional groups. Mg, Mn, Fe, Al, and Si are redistributed into clays that strongly adsorb ions. Microbes contribute to dissolution of insoluble secondary phosphates, possibly via release of organic acids. These reactions significantly impact soil fertility. Below fungi-mineral interfaces, mineral surfaces are exposed to dissolved metabolic byproducts. Through this indirect process, microorganisms can accelerate mineral dissolution, leading to enhanced porosity and permeability and colonization by microbial communities.』

 微生物は、化学・物理風化と粘土成長の速度とメカニズムを変化させ、したがって土壌と堆積物の形成に基本的な役割を演じる。土壌における過程は本来複雑で研究するのが難しいため、我々は、基本的な相互作用を同定するために地衣類−鉱物系に基づいたモデルを使っている。光合成共生体により放出された固定炭素は菌類と他の微生物の成長を促す。これらの微生物は直接または間接に鉱物分離・水和・溶解・二次鉱物生成を引き起こす。細胞外ポリマーによる鉱物表面反応の直接的な媒介を調べるためにモデル多糖類が使われた。多糖類は、pH・鉱物表面構造と組成・有機官能基によって3桁の大きさまで、化学風化速度を抑制または促進できる。Mg・Mn・Fe・Al・Si はイオンを強く吸着する粘土へ再分配される。微生物は、おそらく有機酸の放出によって、不溶性の二次リン酸塩の溶解の一因となる。これらの反応は土壌肥沃度にかなりの影響を与える。菌類−鉱物境界面下で、鉱物表面は溶解した代謝副産物に曝される。この間接的な過程を通じて、微生物は鉱物溶解を促進させることができ、これは孔隙率と浸透率を増加させ微生物群集によるコロニー形成をもたらす。』

Mineral weathering, microbes, and geochemical cycles
 The importance of mineral weathering
 Microbial distributions in natural environments
 Why do microbes interact with minerals?
 Microbial controls on mineral weathering reactions
 Incipient weathering and microbial colonization
 What can we learn from the lichen-mineral microcosm?
Application of insights from the lichen-mineral interface to soils
 Microbial populations in soils
 Which microorganisms are involved?
 Experimental quantification of processes occurring in lichen zones: Insights for rhizosphere processes
 Applications of microbe-mineral interaction studies for the 21st century