title: Quantification of genes and gene transcripts for microbial perchlorate reduction in fixed-bed bioreactors.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Civil, Architectural, and Environmental Engineering, The University of Texas at Austin, Austin, TX, USA. susan.de_long@colostate.edu
authors.forename: S K
authors.initials: SK
authors.lastname: De Long
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Bae
authors.forename: J C
authors.initials: JC
authors.lastname: Brown
authors.forename: L
authors.initials: L
authors.lastname: Raskin
authors.forename: K A
authors.initials: KA
authors.lastname: Kinney
authors.forename: M J
authors.initials: MJ
authors.lastname: Kirisits
mesh_terms: D001419:Bacteria / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D019149:Bioreactors / Q000382:microbiology*; D004265:DNA Helicases / Q000235:genetics; D004269:DNA, Bacterial / Q000032:analysis; D060766:Drinking Water / Q000737:chemistry / Q000382:microbiology*; D005798:Genes, Bacterial; D060587:Groundwater / Q000737:chemistry / Q000382:microbiology; D010472:Perchlorates / Q000378:metabolism*; D016133:Polymerase Chain Reaction / Q000379:methods; D012150:Polymorphism, Restriction Fragment Length; D018508:Water Purification / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D060766:Drinking Water; D010472:Perchlorates; C084217:pcrA protein, Bacteria; C075969:rol protein, Bacteria; D004265:DNA Helicases; C494474:perchlorate