Chlorate

Abstract: Ozone is an excellent disinfectant and can even be used to inactivate microorganisms such as protozoa which are very resistant to conventional disinfectants. Proper rate constants for the inactivation of microorganisms are only available for six species (E. coli, Bacillus subtilis spores, Rotavirus, Giardia lamblia cysts, Giardia muris cysts, Cryptosporidium parvum oocysts). The apparent activation energy for the inactivation of bacteria is in the same order as most chemical reactions (35–50 kJ mol � 1 ), whereas it is much higher for the inactivation of protozoa (80 kJ mol � 1 ). This requires significantly higher ozone exposures at low temperatures to get a similar inactivation for protozoa. Even for the inactivation of resistant microorganisms, OH radicals only play a minor role. Numerous organic and inorganic ozonation disinfection/oxidation by-products have been identified. The by-product of main concern is bromate, which is formed in bromide-containingwaters. A low drinkingwater standard of 10 m gl � 1 has been set for bromate. Therefore, disinfection and oxidation processes have to be evaluated to fulfil these criteria. In certain cases, when bromide concentrations are above about 50m gl � 1 , it may be necessary to use control measures to lower bromate formation (loweringof pH, ammonia addition). Iodate is the main by-product formed duringozonation of iodidecontainingwaters. The reactions involved are direct ozone oxidations. Iodate is considered non-problematic because it is transformed back to iodide endogenically. Chloride cannot be oxidized during ozonation processes under drinking water conditions. Chlorate is only formed if a preoxidation by chlorine and/or chlorine dioxide has occured. r 2002 Elsevier Science Ltd. All rights reserved.

Abstract: Environmental contamination with compounds containing oxyanions of chlorine, such as perchlorate or chlorate [(per)chlorate] or chlorine dioxide, has been a constantly growing problem over the last 100 years. Although the fact that microbes reduce these compounds has been recognized for more than 50 years, only six organisms which can obtain energy for growth by this metabolic process have been described. As part of a study to investigate the diversity and ubiquity of microorganisms involved in the microbial reduction of (per)chlorate, we enumerated the (per)chlorate-reducing bacteria (ClRB) in very diverse environments, including pristine and hydrocarbon-contaminated soils, aquatic sediments, paper mill waste sludges, and farm animal waste lagoons. In all of the environments tested, the acetate-oxidizing ClRB represented a significant population, whose size ranged from 2.31 × 10 3 to 2.4 × 10 6 cells per g of sample. In addition, we isolated 13 ClRB from these environments. All of these organisms could grow anaerobically by coupling complete oxidation of acetate to reduction of (per)chlorate. Chloride was the sole end product of this reductive metabolism. All of the isolates could also use oxygen as a sole electron acceptor, and most, but not all, could use nitrate. The alternative electron donors included simple volatile fatty acids, such as propionate, butyrate, or valerate, as well as simple organic acids, such as lactate or pyruvate. Oxidized-minus-reduced difference spectra of washed whole-cell suspensions of the isolates had absorbance maxima close to 425, 525, and 550 nm, which are characteristic of type c cytochromes. In addition, washed cell suspensions of all of the ClRB isolates could dismutate chlorite, an intermediate in the reductive metabolism of (per)chlorate, into chloride and molecular oxygen. Chlorite dismutation was a result of the activity of a single enzyme which in pure form had a specific activity of approximately 1,928 μmol of chlorite per mg of protein per min. Analyses of the 16S ribosomal DNA sequences of the organisms indicated that they all belonged to the alpha, beta, or gamma subclass of the Proteobacteria . Several were closely related to members of previously described genera that are not recognized for the ability to reduce (per)chlorate, such as the genera Pseudomonas and Azospirllum . However, many were not closely related to any previously described organism and represented new genera within the Proteobacteria . The results of this study significantly increase the limited number of microbial isolates that are known to be capable of dissimilatory (per)chlorate reduction and demonstrate the hitherto unrecognized phylogenetic diversity and ubiquity of the microorganisms that exhibit this type of metabolism.

Abstract: A method was developed to determine the ammonium oxidation rate (potential) of unenriched natural samples by measuring the nitrite produced in shaken slurries. Addition of chlorate to the samples prevented nitrite from being oxidized to nitrate. The effectiveness and specificity of chlorate were tested with pure cultures of nitrite and ammonium oxidizers, as well as in soil and sediment slurries. It was concluded that chlorate had relatively little inhibitory effect on ammonium oxidation. However, under some conditions chlorate was not completely effective in blocking nitrite oxidation, and the causes of this were investigated. The technique was designed to check for incomplete blockage.

Abstract: Chlorate-resistant cell lines were established from survivors after plating allodihaploid cells of Nicotiana tabacum into solid medium containing 20 mM chlorate and amino acids as sole nitrogen source. Data characterizing 9 of the most resistant lines are presented. The mutational origin of these lines was inferred on the basis of the enhancement of the variant frequency by mutagen treatment, and of the persistance of the variant phenotype in cell progeny during growth in the absence of selection for more than 3 years and in plants regenerated from two of the lines. Seven lines completely lacked in vivo nitrate reductase (NR) activity and two lines exhibited low (less than 5% of the wild type) NR activity. The abolition of NR activity was found to be not due to an impaired induction by nitrate. Data reported elsewhere show that one of the NR-negative mutants simultaneously lacks xanthine dehydrogenase activity. This pleiotropic mutation is interpreted to affect the synthesis of a molybdenum-containing cofactor, whereas the 8 other lines carry mutations specifically affecting the synthesis of the NR. Both types of NR-negative mutants were unable to grow on minimal medium containing nitrate as sole nitrogen source, but grew well on amino acids. They proved extremely sensitive to the standard medium containing nitrate and ammonium. Differences between the NR-negative mutants with respect to chlorate resistance suggest that chlorate inhibits cultured N tabacum cells not only via its NR-catalysed conversion to chlorite, but also by NR-independent mechanisms.

Abstract: Chlorate is known to be an in vitro inhibitor of ATP-sulfurylase, the first enzyme in the biosynthesis of PAPS which is the ubiquitous co-substrate for sulfation. Here, the effect of chlorate on protein sulfation in intact cells was investigated. Treatment of various cell cultures with 1 mM sodium chlorate in a medium low in sulfate and sulfur-containing amino acids resulted in an inhibition of protein sulfation greater than 95%. Tyrosine as well as carbohydrate sulfation was blocked. Chlorate did not inhibit protein synthesis and did not exhibit any other toxic effects, even after prolonged treatment of cell cultures. Thus, chlorate treatment provides a powerful tool for studying the biological significance of protein sulfation.