Metabolism, Microflora Effects, and Genotoxicity in Haloacetic Acid-Treated Cultures of Rat Cecal Microbiota

Abstract

Haloacetic acids are by-products of drinking water disinfection. Several compounds in this class are genotoxic and have been identified as rodent hepatocarcinogens. Enzymes produced by the normal intestinal bacteria can transform some promutagens and procarcinogens to their biologically active forms. The present study was designed to investigate the influence of the cecal microbiota on the mutagenicity of haloacetic acids, and to look at changes in the microbiota populations and enzyme activities associated with exposure to haloacetic acids. PYG medium containing 1 mg/ml of monochloroacetic (MCA), monobromoacetic (MBA), dichloroacetic (DCA), dibromoacetic (DBA), trichloroacetic (TCA), tribromoacetic (TBA), or bromochloroacetic (BCA) acid was inoculated with rat cecal homogenate and incubated anaerobically at 37 degrees C. Growth curves were performed with enumeration of the microflora populations on selective media. Mutagenicity in a Salmonella microsuspension bioassay was determined after incubation for various lengths of time, with or without the cecal microbiota. At 15 h of incubation, enzyme assays determined the activities for beta-glucuronidase, beta-galactosidase, beta-glucosidase, azoreductase, nitroreductase, dechlorinase, and dehydrochlorinase. The haloacetic acids, with the exception of BCA, were toxic to the cecal microbiota, and especially to the enterococci. DBA, TBA, and BCA were mutagenic in the microsuspension assay, but the presence of the intestinal flora did not significantly alter the mutagenicity. BCA increased the activities of several enzymes, and therefore has the potential to affect the biotransformation of co-exposed compounds.

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“…The genotypes of the test strains were checked routinely for their histidine requirement, deep rough (rfa) character, UV sensitivity (uvrB mutation), and presence of the R factor. They were stored at À80 C. Salmonella typhimurium TA104 and TA 102 strains are known to be more responsive to certain mutagens such as (2-AA) and (MMS) (Mortelmans et al, 2000;Nelson et al, 2001). Strains TA102 and TA104 contain AT base pairs at the G428 mutant site.…”

Unusual Complex Formation and Chemical Reaction of Haloacetate Anion on the Exterior Surface of Cucurbit[6]uril in the Gas Phase

“…The final concentration for the ESI-MS experiment (water/acetonitrile 1:1 with 1 M formic acid) is adjusted as 50 μM CB [6] with less than 1 % haloacetic acid, which corresponds to~10 mM. All haloacetic acid was carefully handled during performing experiments because of its high toxicity to DNA and metabolism inhibition [31,32].…”