Reduction of (per)chlorate by a novel organism isolated from paper mill waste

As part of a study on the microbiology of chlorate reduction, several new d issimilatory chlorate-reducing bacteria were isolated from a broad diversit y of environments. One of these, strain CKB, was selected for a more comple te characterization. Strain CKB was enriched and isolated from paper mill w aste with acetate as the sole electron donor and chlorate as the sole elect ron acceptor. Strain CKB is a completely oxidizing, non-fermentative, Gram- negative, facultative anaerobe. Cells of strain CKB are 0.5 x 2 mu m and ar e highly motile, with a single polar flagellum. In addition to acetate, str ain CKB can use propionate, butyrate, lactate, succinate, fumarate, malate or yeast extract as electron donors, with chlorate as the sole electron acc eptor. Strain CKB can also couple chlorate reduction to the oxidation of fe rrous iron, sulphide, or the reduced form of the humic substances analogue 2,6-anthrahydroquinone disulphonate. Fe(II) is oxidized to insoluble amorph ous Fe(III) oxide, whereas sulphide is oxidized to elemental sulphur. Growt h is not associated with this metabolism, even when small quantities of ace tate are added as a potential carbon source. In addition to chlorate, strai n CKB can also couple acetate oxidation to the reduction of oxygen or perch lorate. Chlorate is completely reduced to chloride. Strain CKB has an optim um temperature of 35 degrees C, a pH optimum of 7.5 and a salinity optimum of 1% NaCl. Strain CKB can grow in chlorate and perchlorate concentrations of 80 or 20 mM respectively. Under anaerobic conditions, strain CKB can dis mutate chlorite into chloride and O-2, and is only the second organism show n to be capable of this metabolism. Oxidized minus reduced spectra of whole -cell suspensions of strain CKB showed absorbance maxima at 423, 523 and 55 2 nm, which are indicative of the presence of c-type cytochrome(s). Analysi s of the complete sequence of the 16S rDNA indicates that strain CKB is a m ember of the beta subclass of the Proteobacteria. The phototroph Rhodocyclu s tenuis is the closest known relative. When tested, strain CKB could not g row by phototrophy and did not contain bacteriochlorophyll. Phenotypically and phylogenetically, strain CKB differs from all other described bacteria and represents the type strain of a new genus and species.