[show abstract][hide abstract] ABSTRACT: Pseudomonas sp. PDA is an unusual bacterium due to its ability to respire using chlorate under aerobic conditions. The chlorate reductase produced by PDA was shown to be intrinsically different from the enzyme responsible for chlorate and perchlorate [(per)chlorate] reduction produced by Azospira sp. KJ based on subunit composition and other enzyme properties. The perchlorate reductase from strain KJ appeared to have two subunits (100 and 40 kDa) while the chlorate reductase from PDA had three subunits (60, 48, and 27 kDa). N-terminal amino acid sequencing of the 100 kDa protein from strain KJ showed a 77% similarity with the perchlorate reductase alpha subunit from another perchlorate-respiring bacterium, Dechloromonas agitata, while the N-terminus amino acid sequence of the 60 kDa protein from strain PDA did not show a similarity to previously isolated chlorate or perchlorate reductases.
[show abstract][hide abstract] ABSTRACT: The effect of nitrate on perchlorate and chlorate reduction by perchlorate-respiring bacteria (PRB), and on chlorate reduction by chlorate-respiring bacteria (CRB), is not well understood, particularly with respect to the induction of pathways used to degrade these different chemicals. Based on kinetic data obtained in a series of batch tests, we determined that perchlorate respiratory enzymes were inducible (by chlorate or perchlorate) and separate from those used for denitrification by PRB strain Dechlorosoma sp. KJ. Aerobically grown cultures of KJ had lag times of greater than 0.3-2 days when transferred to a medium containing only perchlorate, chlorate, or nitrate as an electron acceptor. There were no lag times for transfers between identical media. Washed cells reduced very little nitrate (<10%) when grown only on chlorate or perchlorate. When grown on nitrate, they degraded little chlorate or perchlorate. The same lack of activity with these electron acceptors was also observed using cell extracts and methyl viologen as an electron carrier, indicating a lack of reactivity was not due to failure of the chemical to diffuse into the cell. Taken together, these results indicated that enzymes for perchlorate and nitrate reduction are separately expressed in strain KJ. The presence of small amounts of nitrate in contaminated groundwater may actually help to increase rates of perchlorate reduction once the nitrate is completely removed. When strain KJ was pre-grown on nitrate and perchlorate, perchlorate degradation (in the absence of nitrate) was more rapid compared to cells grown only on perchlorate. Pseudomonas sp. PDA was unable to degrade perchlorate or grow using nitrate, and the induction of enzymes necessary for chlorate respiration differed for strains KJ and PDA. While chlorate reductase and chlorite dismutase activity were induced in KJ by chlorate or perchlorate under anaerobic conditions, these two enzymes were constitutively expressed by PDA under anaerobic and aerobic conditions independent of the presence of chlorate. To our knowledge, this is the first report of constitutive expression of both chlorate reductase and chlorite dismutase in a bacterium.
Water Research 02/2004; 38(3):673-80. · 4.66 Impact Factor