Characterization of the Chlorate Reductase from Pseudomonas chloritidismutans

Abstract

A chlorate reductase has been purified from the chlorate-reducing strain Pseudomonas chloritidismutans. Comparison with the periplasmic (per)chlorate reductase of strain GR-1 showed that the cytoplasmic chlorate reductase of P. chloritidismutans reduced only chlorate and bromate. Differences were also found in N-terminal sequences, molecular weight, and subunit composition. Metal analysis and electron paramagnetic resonance measurements showed the presence of iron and molybdenum, which are also found in other dissimilatory oxyanion reductases.Pseudomonas chloritidismutans (strain AW-1) is a recently isolated facultative anaerobic chlorate-reducing bacterium (22). In chlorate-reducing bacteria, chlorate is reduced to chlorite by a chlorate reductase, and in a second reaction, chlorite is disproportionated to chloride and oxygen by a chlorite dismutase. Two closely related strains of P. chloritidismutans, Pseudomonas stutzeri DSM 50227 and DSM 5190 T (with 16S ribosomal DNA similarities of 100% and 98.6%, respectively), were not able to grow by dissimilatory chlorate reduction. Accordingly, both P. stutzeri strains lack chlorite dismutase activity. However, in addition to nitrate reductase activity, these strains also showed chlorate reductase activity, which has been observed before for other denitrifying bacteria (6, 15). P. chloritidismutans differed from other (per)chlorate-reducing bacteria in that it was only able to use chlorate as a terminal electron acceptor. Other chlorate-reducing bacteria can also couple the reduction of perchlorate or nitrate to growth (1, 13). Although cell extracts also showed bromate reductase activity, P. chloritidismutans could not grow on bromate (22).Up to now, two enzymes that can reduce chlorate and/or perchlorate have been purified and characterized. A chlorate reductase C has been purified from the denitrifying strain Proteus mirabilis, as well as two nitrate reductases (15). The only known substrate of chlorate reductase C is chlorate, which was reduced to chlorite. It was not demonstrated that Proteus mirabilis was able to couple the reduction of chlorate to growth. A second (per)chlorate reductase has been purified from strain GR-1 (10). Experiments showed that one enzyme is responsible for both chlorate and perchlorate reduction activity. Besides (per)chlorate, nitrate, iodate, and bromate were also reduced by the (per)chlorate reductase of strain GR-1. Perchlorate-grown cells were unable to oxidize nitrate or nitrite, indicating that another nitrate reductase may be involved in nitrate-grown cells (17). The purified chlorate reductase of P. chloritidismutans reported here is the first chlorate reductase derived from a chlorate-reducing bacterium that is capable of only dissimilatory chlorate reduction.P. chloritidismutans (DSM 13592) was grown under strictly anaerobic conditions at 30°C, as described before (1). Strain GR-1 (DSM 11199) was grown as described previously (10, 17). Chlorate (10 mM) was used as the electron acceptor, while acetate (10 mM) was used as the e...

Expression of Chlorite Dismutase and Chlorate Reductase in the Presence of Oxygen and/or Chlorate as the Terminal Electron Acceptor in Ideonella dechloratans

“…One such process could be oxygen-dependent deactivation of Clr. While preparation of Cld seems to be insensitive to oxygen (30), loss of (per)chlorate reductase activity in the presence of oxygen is reported for cell extracts or purified protein preparations from I. dechloratans (31) and other species (19,28,41). This may or may not mirror the in vivo situation during aerobic growth, depending on the actual intracellular concentration of dissolved oxygen and the presence of other cellular components.…”

Anaerobic Metabolism in Haloferax Genus

“…mediterranei could be a good model to remove perchlorate, chlorate and bromate in brines and wastewater even in the presence of low salt concentrations . Due that many wastewater contain both nitrates and chlorates (Wolterink et al, 2003), the processes based on bioremediation by Hfx. mediterranei could replace or even improve protocols where perchlorate and nitrate are removed from brines by ion exchange techniques (Lehman, Badruzzaman, Adham, Roberts & Clifford, 2008).…”

Identification, Characterization, and Classification of Genes Encoding Perchlorate Reductase

“…Similarly, the perchlorate reductase from perc1ace (23) was composed of two subunits, and tryptic peptides obtained from the small subunit exhibited amino acid similarities to reductases, dehydrogenases, and heme proteins. Although the perc1ace tryptic peptide sequences and the Nterminal amino acid sequence of the ␤-subunit of the GR-1 perchlorate reductase have been reported (14,20), the genes encoding this enzyme were not identified for either organism.While genes encoding a chlorate reductase operon were recently reported for the chlorate-reducing organism Ideonella dechloratans (12,35), this enzyme was unable to reduce environmentally significant perchlorate. Furthermore, although microbial nitrate reductases also recognize chlorate as a substrate, it is not known whether perchlorate is similarly recognized (30).…”

“…While genes encoding a chlorate reductase operon were recently reported for the chlorate-reducing organism Ideonella dechloratans (12,35), this enzyme was unable to reduce environmentally significant perchlorate. Furthermore, although microbial nitrate reductases also recognize chlorate as a substrate, it is not known whether perchlorate is similarly recognized (30).…”