Diversity Patterns And Adaptation Mechanisms Of Microbial Communities In Copper Tailings Drainage

Drainage produced by mining and smelting of non-ferrous metals contains a variety of organic,inorganic and heavy metal pollutants,which have an important impact on ecosystem biodiversity and lead to the damage and degradation of ecosystem functions.Microorganisms are the drivers of the bio-geochemistry cycle in the ecosystem.Their distribution patterns reflect the health status of ecosystems.Functional adaptation is the response mechanism of microbial community to environmental changes or threats.The response and adaptation of the microorganisms to the environmental pollution cause changes in the structure and composition of specific functional groups,which drives the assemble process of the structure and diversity of the microbial community.Therefore,the distribution pattern of microbial communities in polluted habitats can reflect the degree of environmental pollution and is an important indicator of the environmental health.In this paper,the species diversity,spatio-temporal dynamic and response mechanism of bacteria,fungi and denitrifier communities in alkaline mine drainage?Alk MD?from Shiba River copper tailings,in Zhongtiao Mountain Copper Base of Yuanqu County,Yuncheng City,Shanxi Province,were systematically studied using molecular ecology theory and method.Aiming at answering the following questions:?1?how did bacterial and fungal communities distribute along the pollution gradient? What factors drive this distribution pattern??2?how did denitrifying microbial community distribute along the pollution gradient? What were the main influencing factors??3?did the distribution pattern and function adaptation of the microbial community respond consistently to environmental changes??4?what were the assemble mechanisms driving the structure and diversity of microbial community in polluted habitats? By analyzing the influence of pollution gradient on the structure and function of microbial community,the key stress factors affecting the spatio-temporal dynamic of different communities were selected.The influence degree of environmental factors,spatial distance and interspecific relationship on the diversity of the community pattern were also analyzed.The results provided a new theoretical basis for revealing the maintenance and adaptation mechanism of microbial community diversity.?1?Seasonal dynamic of the bacterial community and its driving factorsDGGE results showed that the composition,diversity and spatial distribution of the bacterial community have obvious seasonal dynamic.The abundance and ?-diversity of the bacterial community increased along the water flow direction in four seasons,however,the main factors causing this change varied in different months.In May,the main factors were temperature?T?and zinc?Zn?;in July,the main factors were p H and nitrate nitrogen?NO₃^-?;in September,the main factors were total carbon?TC?;in November,the main factors were conductivity?EC?,NO₃^-,nitrite nitrogen?NO₂^-?and sulfate(SO₄^2-).The spatial distribution patterns??-diversity?of the bacterial community between different sampling sites and different seasons were significantly different.NO₂^-,EC,TOC and EC were the main factors affecting the spatial distribution of the bacterial community in May,July,September and November,respectively.In order to further reveal the adaptive mechanism of the bacterial community to pollution gradient,abundant and rare sub-communities were analyzed respectively.The results showed that the main environmental factors affecting abundant sub-community were the same as those affecting the entire community.While the main factors affecting rare sub-community were different from those affecting the entire community.It indicated that abundant bacterial sub-community mainly affected the spatial structure of the entire community,while rare bacterial sub-community mainly affected the ?-diversity of the community.At the same time,spatial distance also had a significant impact on community structure,and the impact on rare sub-community was more obvious.Generally speaking,although diffusion restriction and interspecific interaction also had effects on the spatial distribution of the bacterial community,environmental filtering was the most important driving force affecting the seasonal variation of the bacterial community.?2?Spatial pattern of the bacterial community and its driving factorsHigh-throughput sequencing results showed that the abundance,species composition and diversity of the bacterial community in the upstream?STW1?,midstream?STW2?,downstream?STW3?,upstream seepage water?SUSW?and downstream seepage water?SDSW?of the tailings pond varied significantly along the environmental gradient(p H,EC,NO₃^-,NO₂^-and SO₄^2-formed an obvious gradient along the water flow direction,i.e.,STW1>STW2>STW3>SDSW).The ?-diversity of the bacterial community in SUSW,STW2,STW3 and SDSW was higher than that in STW1.The abundance of the bacterial community increased gradually along the water flow direction.The OTU sequences of all samples belong to 26 different phyla,among which Proteobacteria?average relative abundance 58.95%?was the main bacterial group,and its relative abundance decreased from upstream to downstream gradually.The main reason for this change was that the abundance of Rhodobacter,Hydrogenophaga,Roseococcus and Rhodobaca,which belong to Proteobacteria,decreased gradually along the nitrogen concentration gradient from upstream to downstream.Along the environmental gradient,the bacterial community had distinctly different spatial distribution patterns.The concentration gradients of NO₃^-and NO₂^-were the main factors affecting the spatial pattern diversity of the bacterial community.The results showed that the composition and diversity pattern of the bacterial community in nitrogen-contaminated Alk MD were mainly determined by denitrifying bacteria,which indicated that the importance of ecological niche processes in maintaining the diversity of microbial community was determined by local environmental factors.The results highlight that in severely polluted tailings drainage ecosystems,the gradual screening of the environmental gradients drives the aggregation of similar structural and functional groups in community.?3?Seasonal dynamic of fungal community and its driving factorsThe abundance,structure and distribution pattern of the fungal community had obvious seasonal changes.In May and July,the abundance of the fungal community increased along the water flow direction gradually,while in September and November,the abundance of the fungal community was higher at the intermediate sampling sites?L2 and R2?.The ?-diversity of the fungal community increased gradually from upstream to downstream in the four months.The formation of this pattern was mainly affected by environmental factors.In May,the main factor was the variation of nitrogen content?NO₃^-,NO₂^-and NH4+?;in July,the main factors were the content variation of SO₄^2-and Zn;in September,the main factor was the variation of carbon content?TC,TOC and IC?;in November,the main factors were the content variation of carbon and nitrogen.Environmental step-by-step filtration drove the diversity of the fungal community distribution patterns,but there were differences in major influencing factors in different months,i.e.,p H in May,ammonium nitrogen?NH4+?in July,TOC in September and TC in November.The response mechanisms of dominant and rare sub-communities to environmental change were different.Because the abundant sub-community had wider ecological niche and distribution range,it was less affected by spatial distance.The influence of diffusion restriction on the diversity pattern of the community was mainly reflected on rare sub-community.Different from bacterial community,the key factors driving the structural diversity of the entire fungal community,the abundant and the rare sub-communities were different in May,July and September,respectively.The results showed that the distribution pattern of the abundant and rare sub-communities together determined the diversity of the entire fungal community.The seasonal dynamic of the fungal community was mainly affected by the cadmium?Cd?concentration,indicating that heavy metals still had a significant impact on the community structure even in alkaline tailings drainage with lower concentration of heavy metals.?4?Spatial pattern of the fungal community and its driving factorsThe distribution patterns of the fungal communities at different sampling sites were distinctly different.The ?-diversity in the midstream?STW2?sampling sites of the fungal community was the smallest,indicating that the community structure was relatively simple.The abundance of community gradually increased along the water flow direction.The ?-diversity of the fungal community was influenced by the environmental gradient?mainly formed by TOC,As,NO₂^-and EC?.The dominant fungi were Bullera,Schizangiella,Acremonium and Yarrowia.Their abundance varied significantly along the water flow direction.The spatial pattern of the fungal community was affected by the concentration gradient of IC and Zn.Generally speaking,the spatial pattern of the fungal community was also the result of environmental selection,and the effects of spatial distance and interspecific competition were not obvious.?5?Seasonal dynamic of the denitrifiers community and its driving factorsThe abundance,composition and structure of denitrifiers community containing nir S,nir K and nos Z? functional genes had obvious seasonal changes.The formation of this diversity pattern was mainly related to environmental changes.EC,p H,TOC and TC were the dominant factors for maintaining the diversity pattern of nir S-denitrifiers in May,July,September and November,respectively.p H,Cd,T and NH4+ were the most important factors affecting the spatial distribution of nir K-denitrifiers community in the4 months.SO₄^2-,Cd,NO₂^-and NO₃^-were the most important factors affecting the spatial distribution of nos Z?-denitrifiers in the 4 months.The results showed that the concentration of nitrogen?NO₃^-,NO₂^-and NH4+?was not a limiting factor affecting the distribution pattern of the denitrifiers community in a substrate-rich environment,but the effects of p H,carbon and heavy metals were more obvious.The main factors affecting the distribution pattern of nir S,nir K and nos Z?-denitrifiers community were different,reflecting the different adaptation mechanisms of these different denitrifiers communities.?6?Spatial pattern of the denitrifiers community and its driving factorsThe formation of the spatial pattern of denitrifiers community was mainly determined by the local environmental conditions?p H,TOC,TC,NO₃^-and NO₂^-?which varied significantly along the water flow direction.This indicated that the spatial pattern of the denitrifiers community was driven by environmental selection in Alk MD.The availability of carbon and nitrogen and p H intensity had significant effects on the ?-and ?-diversity of the denitrifiers community.The spatial patterns of nir S and nir K-denitrifiers community were significant affected by p H and NO₂^-,while the spatial pattern of nos ZI-denitrifiers community was significant affected by TOC.The results showed that the changes of the environmental factors were important indicators reflecting the changes in the composition of denitrifiers community.At the same time,the understanding of this pattern formation was helpful to analyze the relationship between microbial community composition changes and functional adaptation in different ecosystems.In summary,in the Alk MD with severe nitrogen pollution,the microbial communities?bacteria,fungi and denitrifiers?had obvious spatio-temporal patterns.Environmental filtering had a more significant impact on the diversity pattern of abundant sub-community,while diffusion restriction had a more significant impact on the diversity pattern of rare sub-community.The response mechanism of denitrifiers to environmental change was consistent with that of the bacterial and fungal communities.Environmental factors affected the structure and diversity of the entire microbial community by affecting the composition and structure of functional microbial populations.Therefore,our results indicated that the structure and function of microbial community were consistent in response to environmental changes.