Quantification of genes and gene transcripts for microbial perchlorate reduction in fixed-bed bioreactors

Abstract

Aims: Optimization of full‐scale, biological perchlorate treatment processes for drinking water would benefit from knowledge of the location and quantity of perchlorate‐reducing bacteria (PRB) and expression of perchlorate‐related genes in bioreactors. The aim of this study was to quantify perchlorate removal and perchlorate‐related genes (pcrA and cld) and their transcripts in bioreactors and to determine whether these genes or transcripts could serve as useful biomarkers for perchlorate treatment processes. Methods and Results: Quantitative PCR (qPCR) assays targeting pcrA and cld were applied to two pilot‐scale, fixed‐bed bioreactors treating perchlorate‐contaminated groundwater. pcrA and cld genes per microgram of DNA were two‐ to threefold higher and three‐ to fourfold higher, respectively, in the bioreactor showing superior perchlorate‐removal performance. In a laboratory‐scale bioreactor, quantities of pcrA and cld genes and transcripts were compared under two distinct performance conditions (c. 60 and 20% perchlorate removal) for a 5‐min empty bed contact time. cld genes per microgram of DNA were approximately threefold higher and cld transcripts per microgram of RNA were approximately sixfold higher under the higher perchlorate‐removal condition. No differences in pcrA genes or transcripts per microgram of DNA or RNA, respectively, were detected between the c. 60 and 20% perchlorate‐removal conditions, possibly because these assays did not accurately quantify pcrA genes and transcripts in the mixed culture present. Conclusions: Quantities of cld genes and transcripts per microgram of DNA and RNA, respectively, were found to be higher when perchlorate removal was higher. However, quantities of pcrA and cld genes or transcripts were not found to directly correlate with perchlorate‐removal rates. Significance and Impact of the Study: To our knowledge, this study represents the first application of qPCR assays to quantify perchlorate‐related genes and transcripts in continuous‐flow bioreactors. The results indicate that cld gene and transcript quantities can provide insights regarding the quantity, location and gene expression of PRB in bioreactors.

Perchlorate Reduction Using Free and Encapsulated Azospira oryzae Enzymes

“…An alternative to ion exchange is the use of biological perchlorate treatment. Biological treatment has been used at sites with concentrations of perchlorate ranging from 50 to 200 000 μg L –1 , which are higher than typical groundwater wells, , and for concentrated brine from regenerative ion exchange processes. , A variety of biological treatment methods have been explored including fixed beds, , bioelectrochemical reduction, and membrane biofilm reactors . However, cocontaminating nitrate also affects biological perchlorate removal, ,, since the microorganisms responsible for perchlorate reduction are facultative anaerobes that preferentially utilize oxygen and nitrate as electron acceptors.…”

Electron donors and co-contaminants affect microbial community composition and activity in perchlorate degradation

“…In addition, the examination of the microbial function and structure in a membrane biofilm reactor revealed the occurrence of the dominant class Betaproteobacteria in the presence of insufficient hydrogen during the degradation of ClO 4 − (Zhao et al 2011). To further analyze the function of microbial communities in the reduction of ClO 4 − and nitrate (NO 3 − ) as well as degradation of ammonia (NH 4 + ), the pcrA gene (encoding perchlorate reductase) and cld gene (encoding chlorite dismutase) had been used to detect PRB and CRB, and the nirS gene (encoding copper and cytochrome cd1 nitrite reductase) had been used to detect denitrifying bacteria (De Long et al 2010;De Long et al 2012;Nozawa-Inoue et al 2008;Zhao et al 2011). However, our knowledge on the changes in the structure of microbial communities and function during ClO 4 − degradation is limited, especially when different electron donors are supplied.…”