Diversity Of Denitrifying Microbial Community In Paddy Soil Polluted By E-waste

In the era of information technology, the update of new electronic products has beenbeing boosted incredible rapid, meanwhile an increasing number of old electronicproducts as e-waste have been disposed. Such disposal contains a serial toxic compounds,including heavy metals like copper (Cu), lead (Pb), cadmium (Cd), mercury (Hg) andpossibly some other organic substances, many of which essentially aggravate soilconditions when inappropriate landfill or e-waste processing. For instance, heavy-metalpollutions in the soil may limit soil nitrification that is essential for atmosphere nitrogencycle on the earth. Here, we have investigated the effect of heavy metal from e-waste onmicrobial involved in this soil nitrification at different stages.In this study, the soil samples were collected from two sites of field (respectivelydesignated LDTR and LGTR), close to e-waste processing plants at Guiyu town inGuangdong Province. Initially, the amount of eight different heavy metals weredetermined, followed by analyzing the structure of microbial communities present incorresponding soil samples via Miseq high-throughput sequencing technique. Thediversity of microbial was determined through analyzing16S rRNA, the expression levelof three key genes in denitrification process was determined, including narG, nirK andnosZ via real time PCR. Moreover, those genes were also examined by comparison withcloning library and T-RFLP. This study determined a few heavy elements impact on thestructure and diversity of soil microbial communities and the soil nitrification, the detailsof which are shown as below:?1? Besides all others seven heavy-metal elements were found far exceeds thebackground value of soil in LDTR and LGTR. Amongst, Hg is the mostover-accumulated element, followed by Cu, Cd, Ni and Zn. Five elements, such as Cu?Zn?Ni?Pb and Cd display a positive correlation in LDTR samples, while Cd?Hg?Pb?Cu and Zn in LGTR. Together these results suggest that these heavy metals likely sharethe same sources of pollution.?2? The Miseq pooled out a total of453,316valid sequence, approximately20,000valid from each sample collected from LDTR, and overall345,838valid sequence,~21,000from each sample collected from LGTR. Through the analysis of16S rRNAsequence, more than200genus in23phylums of microbial were confirmed present insoil. In between LDTR and LGTR, the presence of a few microbial was significantlydiffered, Proteobacteria, Nitrospira, Chloroflexi, Bacteroidetes, Actinobacteriacorrelated with accumulation of heavy metals.?3? In these two sites of soil, The result of Real-time PCR show that theaccumulation of those eight elements hardly had any correlation with the expression ofthree key genes in denitrification process. ?4?The clone libraries suggest that the most abundant was species of clone libraryby narG gene and most proportionally Deinococci contributed the most in LDTR samples,In LGTR, the most abundant species composition was clone library by nirK gene. Thepopulation of Alphaproteobacteria again displayed a growth in two sites.?5? T-RFLP results reveal that Acidovorax sp exhibits a correlation withaccumulation of As, Cd, Cu, Ni, Pb and Zn in terms of decrease in nitrate transferred tonitrite, and Thermus sp. correlates to As, Cd, Cu, Pb and Zn. In LDTR; a correlation ofThermus sp., Hyphomicrobium sp. and Meiothermus sp. was observed with theaccumulation with Cd, Cu, Pb, Zn in reduction of nitrate to nitrite in LGTR. Overall,these results uncover that Thermus, an iron-reducing and acid resistance bacteria mayplay a key role in processing nitrate to nitrite that worth a further investigation.