Isolation and characterization of haloacetic acid-degrading Afipia spp. from drinking water

Haloacetic acids are a class of disinfection byproducts formed during the chlorination and chloramination of drinking water that have been linked to several human health risks. In this study, we isolated numerous strains of haloacetic acid-degrading Afipia spp. from tap water, the wall of a water distribution pipe, and a granular activated carbon filter treating prechlorinated water. These Afipia spp. harbored two phylogenetically distinct groups of α-halocarboxylic acid dehalogenase genes that clustered with genes previously detected only by cultivation-independent methods or were novel and did not conclusively cluster with the previously defined phylogenetic subdivisions of these genes. Four of these Afipia spp. simultaneously harbored both the known classes of α-halocarboxylic acid dehalogenase genes ( deh I and deh II), which is potentially of importance because these bacteria were also capable of biodegrading the greatest number of different haloacetic acids. Our results suggest that Afipia spp. have a beneficial role in suppressing the concentrations of haloacetic acids in tap water, which contrasts the historical (albeit erroneous) association of Afipia sp. (specifically Afipia felis ) as the causative agent of cat scratch disease.     

Mutagenicity of pyridine- and quinoline-carbohydroxamic acid derivatives

11 pyridine- and 6 quinoline-carbohydroxamic acids were tested for mutagenicity on Salmonella typhimurium TA100 and TA98. The results are compared with those obtained for benzohydroxamic acid and 4 naphthohydroxamic acids. Most of them were mutagenic on both these tester strains. Of the pyridine derivatives, pyridine-2-carbohydroxamic acid was the most potent mutagen. Quaternarization of the pyridine-ring nitrogen prevented the induction of mutation to a marked extent. Among the quinoline derivatives, quinoline-6-carbohydroxamic acid showed potent mutagenicity similar to that of 2-naphthohydroxamic acid. The present study supports the proposal made previously that the mechanism for mutagenicity of hydroxamic acids involves Lossen rearrangement of the acid conjugates produced by enzymic acylation (or perhaps phosphorylation or sulfation) of the hydroxamic acids, followed by carbamoylation of the target molecule in the cell by the resultant isocyanate. The multiplicity of factors determining the mutagenic potency of hydroxamic acids is discussed.     

Absence of mutagenic action of 5 beta-cholan-24-oic acid derivatives in the bacterial fluctuation and standard Ames tests

Published data on the mutagenicity of 3 bile acids in the bacterial fluctuation test are conflicting. Eleven 5 beta-cholanoic acids including 2 of the bile acids were assayed for mutagenicity in Salmonella typhimurium TA98 and TA100 in the fluctuation tests. In any of these bile acids at the doses tested, there were no dose-related statistically significant increases in mutagenicity compared with appropriate controls. Similarly, none of these compounds showed positive mutagenicity in both strains in the standard Ames test either with or without hepatic metabolic activation. Our results support the claim that 3 bile acids are not mutagenic, and indicate that the initiation activity of 5 beta-cholanoic acids is not demonstrable with a short-term assay using Salmonella strains.     

Absence of mutagenic action of 5β-cholan-24-oic acid derivatives in the bacterial fluctuation and standard Ames tests

Published data on the mutagenicity of 3 bile acids in the bacterial fluctuation test are conflicting. Eleven 5β-cholanoic acids including 2 of the biie acids were assayed for mutagenicity in Salmonella typhimurium TA98 and TA100 in the fluctuation tests. In any of these bile acids at the doses tested, there were no dose-related statistically significant increases in mutagenicity compared with appropriate controls. Similarly, none of these compounds showed positive mutagenicity in both strains in the standard Ames test either with or without hepatic metabolic activation. Our results support the claim that 3 bile acids are not mutagenic, and indicate that the initiation activity of 5β-cholanoic acids is not demonstrable with a short-term assay using Salmonella strains.     

Lack of mutagenic activity of bile acids in bacterial fluctuation tests

3 bile acids (cholic acid, chenodeoxycholic acid and deoxycholic acid) were assayed for mutagenicity in Salmonella typhimurium TA98 and TA100 in fluctuation tests in the absence of an external source of metabolic activation. At the doses tested, there were no dose-related statistically significant increases in mutagenicity compared with appropriate controls. These results do not support the claim (Watabe, J., and H. Bernstein (1985) Mutation Res., 158, 45-51) that these bile acids are mutagenic.     

Phage T7-inactivation test. A possibility of quantitative mutagenicity screening

A new method is described for the quantitative characterization of the genotoxic effect of chemicals. The method is based on the determination of the inactivation of bacteriophage T7 and on the application of a simple mathematical model valid for the processes during, or at least in the initial stage of the interaction of chemicals and phages. A value characteristic for the chemical is defined and it is determined from the inactivation kinetics. Typical inactivation kinetic curves and some problems of the application of the model as well as the mutagenicity index values determined for about 30 substances are presented. The substances examined have mutagenicity index values covering a range of six orders of magnitude. The obtained values are compared with the results of different mutagenicity/carcinogenicity tests and discussed on the basis of data in the literature. The presented method is proposed to be applied for quantitative mutagenicity screening of chemicals.     

Measurements of Mutagenic and Antimutagenic Activities of Bile Acids by Rec-assay

To study the carcinogenic activity of bile acids, we examined the mutagenic activity of bile acids by Rec-assay using B. subtilis H17 and M45 strains. Cholic, chenodeoxycholic, lithocholic, and glycolithocholic acids exerted much weaker mutagenicity than mitomicin C (MMC), and deoxycholic and glycodeoxycholic acids showed toxicity toward the bacteria. Most of the conjugated bile acids (glycocholic, taurocholic, and taurodexycholic acids) and their amino acid components (glycine and taurine) were neither toxic nor mutagenic. No bile acids enhanced the mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), but glycine enhanced both toxicity and mutagenicity of MNNG in a dose-dependent manner. On the other hand, taurine decreased the mutagenicity of MNNG, and most of the bile acids decreased the mutagenicity of MMC. Furthermore, taurocholic acids decreased toxicity and/or mutagenicity of other bile acids. These results suggested that the mutagenic and comutagenic activities of bile acids can be disregarded, but they are antimutagenic in some situations.     

Study of the causes of direct-acting mutagenicity in coffee and tea using the Ara test in Salmonella typhimurium

The mutagenic activities of 6 of the chemicals identified in coffee solutions were assayed with the Salmonella Ara test, under experimental conditions optimized for coffee mutagenicity. Caffeine was the only non-mutagenic compound. Among the other 5 chemicals, hydrogen peroxide was the strongest mutagen and chlorogenic acid the weakest; methylglyoxal, glyoxal and caffeic acid exhibited intermediate mutagenicities. The minimal mutagenic doses of these components correlated negatively with their relative concentrations in coffee. It was concluded that chlorogenic acid, caffeic acid, glyoxal and methylglyoxal cannot contribute alone to the mutagenicity of coffee in the Ara test, since their minimal mutagenic concentrations were much higher than their respective levels in the coffee samples assayed. By contrast, 40-60% of the mutagenic activity in coffee and also in tea could be attributed to their H2O2 contents. Catalase abolished more than 95% of the mutagenic activity of coffee, as detected by the Ara test. A similar sensitivity to catalase has been reported by other authors in relation to the coffee mutagenicity identified by the Salmonella His test. Nevertheless, the results presented in this paper suggest that the Ara forward and the His reverse mutation tests are sensitive to the mutagenicity of different constituents in coffee solutions. We propose that the His test, sensitive at high coffee doses, mainly recognizes the mutagenicity of methylglyoxal, whilst the Ara test, sensitive at low coffee doses, mainly detects the mutagenic activity of hydrogen peroxide. The data reported also suggest that the direct-acting mutagenicity(ies) detected by the Ara test in tea solutions is (are) based on similar, if not identical, mechanisms.     

Quantitative studies on competitive ligand binding to bovine serum albumin by use of the spin label 5-doxyl dodecanoic acid.

The binding of the spin label 5-doxyl dodecanoic acid to bovine serum albumin in phosphate buffer at pH 7.4 was studied by electron spin resonance spectroscopy. Free label and label bound to serum albumin could be quantitatively measured and evaluated from the superposition spectra of these two species with no previous separation. The efficiency relative to the spin label as competitors for binding to serum albumin was studied with salicylic acid and some fatty acids of medium length. The results were represented both by the stoichiometric model involving equilibrium constants Ki, by binding isotherms constructed from the Ki values, and by a purely graphical representation of the experimental data points without connection with any special binding model.     

Structure-based methods for predicting mutagenicity and carcinogenicity: are we there yet?

There is a great deal of current interest in the use of commercial, automated programs for the prediction of mutagenicity and carcinogenicity based on chemical structure. However, the goal of accurate and reliable toxicity prediction for any chemical, based solely on structural information remains elusive. The toxicity prediction challenge is global in its objective, but limited in its solution, to within local domains of chemicals acting according to similar mechanisms of action in the biological system; to predict, we must be able to generalize based on chemical structure, but the biology fundamentally limits our ability to do so. Available commercial systems for mutagenicity and/or carcinogenicity prediction differ in their specifics, yet most fall in two major categories: (1) automated approaches that rely on the use of statistics for extracting correlations between structure and activity; and (2) knowledge-based expert systems that rely on a set of programmed rules distilled from available knowledge and human expert judgement. These two categories of approaches differ in the ways that they represent, process, and generalize chemical-biological activity information. An application of four commercial systems (TOPKAT, CASE/MULTI-CASE, DEREK, and OncoLogic) to mutagenicity and carcinogenicity prediction for a particular class of chemicals—the haloacetic acids (HAs)—is presented to highlight these differences. Some discussion is devoted to the issue of gauging the relative performance of commercial prediction systems, as well as to the role of prospective prediction exercises in this effort. And finally, an alternative approach that stops short of delivering a prediction to a user, involving structure-searching and data base exploration, is briefly considered.     

The mutagenicity of bile acids using a fluctuation test

The mutagenicity of bile acids was detected by a fluctuation test using Salmonella typhimurium TA100 and TA98 as tester strains. Cholic acid, chenodeoxycholic acid, deoxycholic acid and ursodeoxycholic acid were mutagenic in this test while lithocholic acid was not. The mutagenicity of the bile acids on a molar basis was roughly one-fourth that of methyl methanesulfonate, a moderately potent mutagen. Epidemiological studies have shown a high correlation between levels of bile acids excreted and colon cancer. However, no evidence has previously been reported showing that bile acids are mutagenic. Our results suggest that bile acids may be important in the etiology of colon cancer.     

Modeling of batch fermentation kinetics for succinic acid production by Mannheimia succiniciproducens

Kinetic models are proposed for the batch production of succinic acid from glucose by Mannheimia succiniciproducens MBEL55E. The models include terms accounting for both substrate and product inhibitions. Experimental data collected from a series of batch fermentations with different initial glucose concentrations were used to estimate parameters and also to validate the models proposed. The optimal values of the parameters were approximated by minimizing the discrepancy between the model predictions and corresponding experimental data. The growth of M. succiniciproducens could be expressed by a modified Monod model incorporating inhibitions of glucose and organic acids accumulated in the culture broth. The Luedeking–Piret model was able to describe the formation of organic acids as the fermentation proceeded, in which succinic, acetic, and formic acids followed a mixed-growth-associated pattern. However, unexpectedly, lactic acid fermentation by M. succiniciproducens was nearly nongrowth-associated. In all cases, the model simulation matched well with the experimental observations, which made it possible to elucidate the fermentation characteristics of M. succiniciproducens during efficient succinic acid production from glucose. These models thus can be employed for the development and optimization of biobased succinic acid production processes.