Dechloromonas hortensis sp. nov. and strain ASK-1, two novel (per)chlorate-reducing bacteria, and taxonomic description of strain GR-1 Recent studies on the occurrence of (per)chlorate-reducing bacteria have resulted in the characterization of strains capable of dissimilatory (per)chlorate reduction. Phylogenetic analysis has shown that these bacteria are members of the Proteobacteria. Strains have been isolated from polluted and pristine sites, but only strains from polluted sites have been characterized in detail and deposited in culture collections. Herein we describe the isolation and characterization of perchlorate-reducing bacterium strain MA-1 T and chlorate-reducing bacterium strain ASK-1, respectively isolated from a pristine and a chlorate-polluted site. Both isolates are members of the Proteobacteria. The 16S rRNA gene sequence similarity of MA-1 T to Dechloromonas agitata DSM 13637 T is 97?6 %, but the relatedness in DNA-DNA reassociation is only 37 %. Therefore, we propose to classify strain MA-1 T (=DSM 15637 T =ATCC BAA-776 T ) as the type strain of a novel species, Dechloromonas hortensis sp. nov. Strain ASK-1 and a previously described strain GR-1 show 100 and 99 % 16S rRNA gene sequence similarity to Pseudomonas chloritidismutans DSM 13592 T and Dechlorosoma suillum DSM 13638 T , respectively. DNA-DNA hybridization studies indicated that strains ASK-1 and GR-1 are related at the species level to P. chloritidismutans DSM 13592 T (79 %) and Dechlorosoma suillum DSM 13638 T (85 %), respectively. As suggested previously, Dechlorosoma suillum appears to be a later heterotypic synonym of Azospira oryzae. Although strain ASK-1 is identified as P. chloritidismutans, its morphology and growth requirements are different from those of the type strain.The occurrence of perchlorate and chlorate in natural environments is due mainly to human activities. Chlorate is used as a herbicide, as a catalyst in matches and for onsite production of chlorine dioxide (ClO 2 ), a bleaching agent employed in the paper and pulp industries. Perchlorate is used as rocket propellant in the defence and aerospace industries. In the United States, discharge of perchlorate-containing waste streams has been identified as the major source of perchlorate contamination in drinking water supplies (Renner, 1998; US Environmental Protection Agency, 2000). Chlorate and perchlorate are highly soluble and chemically stable under environmental conditions (Urbansky, 2002). Remediation strategies by chemical reduction or by adsorption to activated carbon are either too slow or incomplete (Urbansky, 1998). Recent research has shown that bioremediation may be the most economically feasible, fastest and easiest means of treating (per)chlorate-contaminated sites and water sources (Coates & Achenbach, 2004). (Per)chlorate-reducing bacteria are able to perform aThe GenBank/EMBL/DDBJ accession numbers of the 16S rRNA gene sequences of strains ASK-1, MA-1 and GR-1 are AY277620, AY277621 and AY277622.Photographs of colonies and cell extracts of P. chl...

Microbial dehalogenation of tetrachloroethene (PCE) and cis-dichloroethene (cis-DCE) was studied in cultures from a continuous stirred tank reactor initially inoculated with aquifer material from a PCE-contaminated site. Cultures amended with hydrogen and acetate readily dechlorinated PCE and cis-DCE; however, this transformation was incomplete and resulted in the accumulation of chlorinated intermediates and only small amounts of ethene within 60 days of incubation. Conversely, microbial PCE and cis-DCE dechlorination in cultures with benzoate and acetate resulted in the complete transformation to ethene within 30 days. Community fingerprinting by denaturing gradient gel electrophoresis (DGGE) revealed the predominance of phylotypes closely affiliated with Desulfitobacterium, Dehalococcoides, and Syntrophus species. The Dehalococcoides culture VZ, obtained from small whitish colonies in cis-DCE dechlorinating agarose cultures, revealed an irregular cell diameter between 200 and 500 nm, and a spherical or biconcave disk-shaped morphology. These organisms were identified as responsible for the dechlorination of cis-DCE to ethene in the PCE-dechlorinating consortia, operating together with the Desulfitobacterium as PCE-to-cis-DCE dehalogenating bacterium and with a Syntrophus species as potential hydrogen-producing partner in cultures with benzoate.