Study On The Influencing Mechanism Of Physicochemical Factors On The Biofilm Formation Of Acidianus Manzaensis On Metal Sulfides

The early-stage attachment behaviors of acidophiles on mineral surfaces and the subsequent biofilm formation play important roles in the biological corrosion of minerals,and also can improve the leaching efficiency of metal sulfides.Recent studies have found that physicochemical factors（such as Ag⁺,Tween-20,pine oil,ethyl xanthate and oxygen condition）could affect the bioleaching of metal sulfides,while its effects on biofilm formation were unclear.Therefore,the effect of Ag⁺,tween-20,pine oil,ethyl xanthate and oxygen condition on the adhesion behaviors and biofilms formation of Acidianus manzaensis on chalcopyrite and pyrite surface and their possible mechanisms were investigated,which will lay a theoretical foundation for the better application of bioleaching.The main research contents and results are as follows:（1）Ag⁺could significantly promote the attachment of cells on chalcopyrite and pyrite,and the optimum concentration of Ag⁺was 2 mg/L with the biggest percentage of attached cells（74%and 80%,respectively）,whereas that for the control（0 mg/L）was only 61%and 65%,respectively.When Ag⁺was added,the mineral surface properties changed,resulting in changing Lewis acid-base interaction and increasing the adhesion force between A.manzaensis and minerals and promoting the formation of biofilm.The live/dead ratio of biofilm was small,suggesting that dead cells were a great slice during the whole life-cycle of biofilm on chalcopyrite.Moreover,Ag⁺catalyzed mineral corrosion and accelerated biofilm formation by producing a loose porous Ag₂S layer.（2）The bacterial adhesion experiments showed that 2 mg/L of Tween-20 increased the adhesion percentage on chalcopyrite and pyrite（by 7%and 9%,respectively）of A.manzaensis.Tween-20 could promote the early adhesion of A.manzaensis and biofilm formation on the mineral surface by changing the Lewis acid-base interaction and electrostatic force to increase total interaction energy and adhesion force.Furthermore,the promotion of biofilm formation on chalcopyrite by Tween-20 was mainly attributed to the reduction of S⁰ passivation layer formation and complexing more Fe³⁺on the chalcopyrite surface,contributing to the erosion of chalcopyrite and creating more corrosion pits.The main reason why Tween-20 promoted the formation of pyrite biofilm was that Tween-20 promoted the adhesion of A.manzaensis on pyrite and formed dense biofilm,resulting in pyrite corrosion.（3）Pine oil showed negative impacts on the adsorbed amount of A.manzaensis on the mineral surface,and the percentage of adsorbed cells decreased as the concentration of pine oil increased after adhesion equilibrium.When the concentration of pine oil was 0.01 mg/L,the percentage of attached A.manzaensis on chalcopyrite and pyrite was 55%and 62%,respectively.The addition of pine oil could decrease the negative charge of sulfide ore and cells,and enhance the attraction of acid-base interaction and adhesion force.As for biofilm formation of A.manzaensis,the addition of 0.01 mg/L pine oil delayed the formation of cell microcolonies in the first stage.However,as biofilm grew,the biofilm coverage was larger with the addition of pine oil than the control.In addition,the microcolonies on the mineral surface were larger and the corrosion pits were bigger with the addition of pine oil.（4）The adhesion percentage of A.manzaensis on the mineral surface after adsorption equilibrium reduced along with ethyl xanthate concentration because of the toxicity of ethyl xanthate to A.manzaensis.When the concentration of ethyl xanthate was 0.01 mg/L,the percentage of attached A.manzaensis on chalcopyrite and pyrite was 56%and 60%,respectively.While the low concentration（0.01 mg/L）of ethyl xanthate had little effect on the growth of A.manzaensis.The addition of ethyl xanthate could enhance the hydrophobicity of sulfide ore,resulting in increasing total interaction energy and adhesion force.The addition of ethyl xanthate delayed the formation of microcolonies on sulfide ore.While biofilm coverage was larger with the addition of ethyl xanthate than the control when biofilm was mature.In addition,more and larger microcolonies were observed on the mineral surface when ethyl xanthate was added,resulting in an increasing corrosion degree of the mineral surface.（5）The adsorption capacity of aerobic adapted A.manzaensis on chalcopyrite and pyrite surface（77%and 80%）was larger than that of anaerobic adapted A.manzaensis（53%and 56%）.Compared with anaerobic adapted A.manzaensis,the surface of aerobic adapted A.manzaensis appeared to be more hydrophobic because of more tyrosine,tryptophan protein-like substances and humic acid-like organics,which increased adhesion force.The A.manzaensis under aerobic conditions had a denser biofilm on the sulfide ore surface.And there were obvious corrosion pits on the sulfide ore surface.However,there was no obvious corrosion under anaerobic conditions.In addition,we explored the reason why there were more humic acid-like organics in extracellular polymeric substances（EPS）of aerobic adapted A.manzaensis.It was found that the expression level of genes related to tyrosine（an important precursor of biosynthesis of humic acid organics）synthesis was higher in aerobic adapted A.manzaensis.And more tyrosine protein-like substances were detected in the cytoplasm of aerobic adapted A.manzaensis.According to the above studies,we revealed the mechanism by which key physicochemical factors（Ag⁺,Tween-20,pine oil,ethyl xanthate and oxygen condition）could affect the initial attachment of microorganisms on mineral surfaces and the formation of biofilms by affecting the surface properties of microorganisms and minerals;corrosion of mineral surfaces was found closely related to the coverage of biofilm.The research in this paper provided a theoretical basis for the regulation of bio-corrosion of sulfide ores.