Molecular assessment of salt-tolerant, perchlorate- and nitrate-reducing microbial cultures

The microbial ecology of enrichment cultures adapted to the removal of perchlorate and nitrate from high salt solutions and ion-exchange brines was examined over a period of four years using denaturing gradient gel electrophoresis and total DNA extraction with cloning and in each case partial sequencing of the 16S rDNA genes. The cultures studied were a result of enrichment from marine sediment inoculum initiated in 2001. The resulting enrichment cultures were fed perchlorate, or perchlorate and nitrate, in a 3% (w/v) NaCl defined medium or ion-exchange brines (5.6% NaCl) containing perchlorate and nitrate with acetate as the electron donor. All of the sequences' closest matches in the NCBI GenBank database were to marine or salt-tolerant organisms. Strains belonging to the genera Halomonas or Marinobacter were found to dominate in cultures that were fed nitrate in addition to perchlorate, but were effectively absent from cultures fed perchlorate alone. The cultures fed perchlorate as the sole electron acceptor were relatively diverse with the dominant sequences belonging to the genera Dechloromarinus and Denitromonas. A study examining the effects of growing the cultures on different electron acceptors to the cultures revealed that Denitromonas may be more dominant than Dechloromarinus as the salt-tolerant, perchlorate-reducing organism.