微生物-矿物相互作用:机制与重金属固定效应

Microbe-mineral interactions:Mechanisms and immobilization effect toward heavy metals

微生物-矿物相互作用是地表中最基本的地球化学过程,影响着重金属的迁移转化与生态效应.重金属胁迫下,微生物演化出了一系列适应机制,改变着矿物的表面反应活性,而矿物反过来刺激着微生物的分泌活动.在两者的协同作用下实现了对重金属的钝化.本文综述了微生物-矿物相互作用机制,并重点总结了微生物-硅酸盐矿物、微生物-铁矿物体系中微生物和矿物的协同作用对重金属的固定机制.微生物与矿物之间的作用机制主要包括生物力学和生物化学作用.一些真菌、放线菌能利用菌丝沿着矿物晶面、解理、裂缝和晶界,在纳米尺度上对矿物进行穿插、挤压、剥蚀等生物力学作用,甚至形成矿物隧道化.而大多数微生物主要通过分泌铁载体、有机酸以及氧化还原作用改造矿物.两者相互作用改变着矿物表面及微生物活性,影响着重金属的形态.微生物-硅酸盐矿物体系主要通过提高固有活性位点利用率,增加额外吸附位点,改变与重金属的作用方式,影响矿物或微生物内部分散性,破坏矿物的结构,改变微生物的分泌活动等方式实现重金属的钝化.而微生物-铁矿物体系则主要通过加速电子转移的方式促进变价金属向低毒或无毒形态转变.期望本综述能为微生物-矿物联合修复重金属污染提供理论支持.

Microbial-mineral interactions have recently demonstrated to play a critical role in affecting the migration,transformation characteristics and environmental impacts of heavy metals,via formation of“microbial-mineral”binary complexes or“microbial-mineral-organic matter”multiple complexes.Microbes have evolved a series of adaptation mechanisms and survival strategies under heavy metal stress,during which minerals are modified and heavy metals immobilized.In such situation,minerals not only provide nutrients for microbial growth,but could also act as an important protective umbrella for microbes against toxicity of heavy metals or other pollutants.In this review paper,the interaction mechanisms between microorganisms and minerals were first introduced.Subsequently,the synergistic effect and mechanisms of microbe and mineral in heavy metal immobilization were highlighted via microbial-silicate mineral and microbial-iron mineral systems.Mechanisms of microbial interaction with minerals are quite complex,and there are two synergistic actions by which microorganisms can decompose mineral substrates:physical and biochemical.Biophysical weathering of minerals commonly occurs in the interaction of fungi and actinomycetes with minerals.Fungi and actinomycetes can break minerals through fungal hyphae penetration and growth along crystal planes,cleavage,cracks and grain boundaries,mechanically boring and denudating the rocks at the nanoscale,leaving the cracks and tunnels inside.As for the majority of heterotrophic microorganisms,the biochemical route for mineral dissolution is dominated by leaching,which is enforced by three main mechanisms.That is,the secretion of siderophores,organic/inorganic acids and redox actions.These mechanisms strongly accelerate dissolution of mineral,causing the formation of“metal sink”around the microbial biomass.The“metal sink”in return,works as nutrient sources to promote the growth of microorganisms.Importantly,the intimate interaction between microbial and soil mineral significantly alters the surface reactivity of mineral and microbial activity,and therefore leads to the immobilization and changes of speciation and bioavailability of heavy metals.Microbial-silicate mineral and microbial-iron mineral systems were employed to ascertain why microbe-mineral systems possess such merits in heavy metals remediation than single microbe or mineral system.In microbial-silicate mineral system,the interaction of microbe and silicate promotes heavy metal remediation depends primarily upon the following mechanisms:1)provide additional adsorption sites such as hydroxyl,carboxyl,sulfhydryl,phosphorus acyl.2)increase the utilization rate of inherent active sites.3)change the binding characteristics of heavy metals with minerals,for example,negatively charged microorganisms can act as intermediates to bridge heavy metal ions with minerals,forming stabilized monodentate or multidentate complexes.4)affect the dispersion or agglomeration status of mineral particles and microorganisms.5)change the original structure of mineral,like the exfoliation of silicate layers of 2D silicate minerals,or even destroy the lattice structure.6)make adjustments on the type and content of secretion and excretion products to regulate the microbial activities under the stimulation of direct contact with minerals.While the microbial-iron mineral systems tend to promote the metal or nonmetallic pollutants with variable valence states from toxic forms to less toxic ones by accelerating the electron transfer.This paper aims to provide a solid theoretical and scientific basis for microbial-mineral remediation of heavy metal pollution.