Showing papers on "Bacteria published in 1980"
TL;DR: Use of DAPI improved visualization and counting of <1-µm bacteria and blue-green algae in seston-rich samples and extended sample storage to at least 24 weeks.
Abstract: A highly specific and sensitive fluorescing DNA stain, 4′6-diamidino-2-phenylindole (DAPI) was compared with acridine orange (AO) for counting aquatic microflora. Use of DAPI improved visualization and counting of <1-µm bacteria and blue-green algae in seston-rich samples and extended sample storage to at least 24 weeks.
5,119 citations
698 citations
TL;DR: Results demonstrate that active export of tetracycline is a common component of the mechanism for tetrACYcline resistance encoded by different plasmid-borne determinants in bacteria.
Abstract: Tetracycline resistance encoded by four genetically different determinants residing on plasmids in Escherichia coli was shown to be associated in each case with an energy-dependent decrease in accumulation of the antibiotic in whole cells in which resistance had been induced. The different class determinants examined were those on plasmids RP1 (class A), R222 (class B), R144 (class C), and RA1 (class D). This decrease in accumulation was attributable to an active efflux, because everted (inside-out) membrane vesicles made from tetracycline-induced E. coli cells containing any one of the four plasmids were shown to concentrate tetracycline by an active influx. This active uptake was not seen in inside-out vesicles from sensitive cells or uninduced R222-containing cells. In vesicles from induced R222-containing cells, the efflux appeared to be carrier-mediated with a Km of about 6 microM. These results demonstrate that active export of tetracycline is a common component of the mechanism for tetracycline resistance encoded by different plasmid-borne determinants in bacteria.
593 citations
TL;DR: Antibiotic G418 is a 2-deoxystreptamine antibiotic that is structurally related to gentamicin but has inhibitory activity against a much wider variety of pro- and eukaryotic organisms.
Abstract: Some eukaryotic genes can be expressed in bacteria but there are few examples of the expression of prokaryotic genes in eukaryotes1. Antibiotic G418 is a 2-deoxystreptamine antibiotic that is structurally related to gentamicin2 but has inhibitory activity against a much wider variety of pro- and eukaryotic organisms. In bacteria, resistance to G418 can be determined by several plasmid-encoded modifying enzymes3 and, in view of the broad spectrum of activity of G418, we considered that this antibiotic might be useful as a selective agent for the introduction of these antibiotic resistance genes into a eukaryotic organism such as Saccharomyces cerevisiae. Additional impetus for these experiments came from the knowledge that certain of the G418-resistance determinants in bacteria are carried on transposable elements4; a study of the properties of these elements in eukaryotes would be intriguing.
414 citations
TL;DR: A combination of morphology, salt tolerance, and guanine plus cytosine content supports the establishment of a new genus, Halomonas, in Family II (Vibrionaceae) of part 8, Gram-Negative Facultatively Anaerobic Bacteria, of Bergey's Manual (8th edition).
Abstract: The morphological, biochemical, and physiological characteristics of nine bacterial strains isolated from a solar salt facility located on Bonaire, Netherlands Antilles are described. The bacteria were gram-negative rods which produce white, opaque colonies on solid media. During the log phase of growth, the cultures consisted of single and paired cells with polar flagella predominating. Older cultures characteristically produced highly elongated, flexible rods. All of these strains reduced NO3 to NO2, grew anaerobically in the presence of NO3, and fermented glucose but oxidized sucrose, glycerol, mannose, and cellobiose. All strains were ornithine and lysine decarboxylase positive, catalase positive, and cytochrome oxidase negative. Eight of the nine strains grew in a complex Casamino Acids liquid medium containing from 0 to 32% (wt/vol) solar salt at temperatures from 23 to 37°C; the ninth strain was restricted in its growth to 0 to 20% solar salt. The guanine plus cytosine content of the deoxyribonucleic acid was 61 ± 1 mol%. This combination of morphology, salt tolerance, and guanine plus cytosine content supports the establishment of a new genus, Halomonas, in Family II (Vibrionaceae) of part 8, Gram-Negative Facultatively Anaerobic Bacteria, of Bergey's Manual (8th edition). The type species of this genus is H. elongata, the type strain of which is isolate 1H9 (= ATCC 33173). Strain 1H15 is regarded as belonging to a biovar of H. elongata on the basis of its production of lophotrichous cells and its inability to grow at 37°c in the presence of 32% solar salt.
405 citations
TL;DR: A versatile stain has been developed for demonstrating pollen, fungal hyphae and spores, bacteria and yeasts, and the concentration of lactic acid in the stain mixture plays an important role in the differential staining of pollen.
Abstract: A versatile stain has been developed for demonstrating pollen, fungal hyphae and spores, bacteria and yeasts. The mixture is made by compounding in the following order: ethanol, 20 ml; 1% malachite...
357 citations
01 Jan 1980
354 citations
TL;DR: The present study focuses on the development of the Phosphotransferase System in E. coli with a focus on the components of the Lactose-Proton Coupling process.
287 citations
TL;DR: Experiments with other cell lines of human, monkey, and mouse origin, and also with bacteria harboring another recombinant plasmid, indicate that DNA transfer from bacteria to mammalian cells is a general phenomenon.
Abstract: Induction of a virus infection by cloned simian virus 40 DNA was chosen as a test system to detect transfer of genes from bacteria to cultured mammalian cells. Escherichia coli cells containing a recombinant plasmid with three tandem inserts of simian virus 40 DNA were able to infect CV-1 monkey cells under various conditions. The gene transfer was resistant to DNase I and therefore seems not to occur via free DNA but most likely via uptake of whole bacteria, followed by release of plasmid DNA and generation of infectious circular simian virus 40 DNA in a recombination-excision process. Spontaneous transfer was found to be infrequent, 4 x 10(9) bacteria yielding one infection per 10(7) monkey cells. The frequency was greatly increased by adding bacteria as a calcium phosphate coprecipitate or by fusion of lysozyme-treated bacteria (protoplasts) with monkey cells in the presence of polyethylene glycol. With the latter technique, 10(4) protoplasts gave rise to one infection per 15 monkey cells. Experiments with other cell lines of human, monkey, and mouse origin, and also with bacteria harboring another recombinant plasmid, indicate that DNA transfer from bacteria to mammalian cells is a general phenomenon.
279 citations
TL;DR: Identification of bacterial populations before and after contact with chlorine (1 to 2 mg/liter) for 1 h revealed that chlorination selected for gram-positive bacteria.
Abstract: Nearly 700 standard plate count (SPC) bacteria were isolated from drinking water and untreated surface water and identified according to a scheme developed to permit the rapid, simple classification of microorganisms to genus, species, or group. Actinomycetes and Aeromonas species were the two most common groups of SPC bacteria in chlorinated distribution water. Aeromonas spp. and Enterobacter agglomerans were the two most common groups of SPC bacteria in raw water. Identification of bacterial populations before and after contact with chlorine (1 to 2 mg/liter) for 1 h revealed that chlorination selected for gram-positive bacteria. Water that contained high densities of bacteria known to be antagonistic to coliforms had low coliform isolation rates. The membrane filtration technique for enumerating SPC bacteria recovered significantly higher numbers (P
TL;DR: In 11 species of rumen ciliates belonging to nine genera of the family Ophryoscolecidae an ectosymbiosis with methanogenic bacteria was found, which may reflect a metabolic interaction in which efficient interspecies hydrogen transfer benefits both partners.
Abstract: In 11 species of rumen ciliates belonging to nine genera of the family Ophryoscolecidae (order Entodiniomorphida) an ectosymbiosis with methanogenic bacteria was found. The bacteria could be identified as methanogens on the basis of the presence of specific fluorescent coenzymes (F350 and F420). This somatic interaction may reflect a metabolic interaction in which efficient interspecies hydrogen transfer benefits both partners. Images
TL;DR: Urinary mucus, and probably mucous material elsewhere, may function as a trap for Enterobacteriaceae with type 1 fimbriae by the specific adherence of such bacteria, a nonimmune resistance mechanism against disease caused by Enterob bacteria.
Abstract: Two Escherichia coli O6:K2:H1 strains, C1212 and C1214, isolated from urinary tract infections, were compared for their capacity to adhere to various cells. After growth on solid medium, only C1212 bacteria agglutinate human erythrocytes and attach to urinary epithelial cells. Both of these reactions are mannose resistant. In contrast, C1214 bacteria cause a mannose-sensitive agglutination of guinea pig erythrocytes, show a mannose-sensitive attachment to buccal epithelial cells, and attach to urinary mucus. Immunoelectron microscopy revealed that C1214 bacteria possess type 1 fimbriae (mannose sensitive), which are not present in C1212 bacteria when this strain is grown on solid medium. The fimbriae of C1212 (mannose resistant) were also demonstrated by immunoelectron microscopy. We call these fimbriae demonstrated in C1212 the E. coli F7 antigen. Urinary mucus, and probably mucous material elsewhere, may function as a trap for Enterobacteriaceae with type 1 fimbriae by the specific adherence of such bacteria. We consider this a nonimmune resistance mechanism against disease caused by Enterobacteriaceae.
TL;DR: It is proposed that these organisms form a single species belonging to a new genus, for which the name Renibacterium is proposed, which is most closely related to the Coryneform Group of Bacteria.
Abstract: Isolates of the kidney disease bacterium, the causative agent of bacterial kidney disease in salmonid fishes, were characterized by the guanine plus cytosine content of the deoxyribonucleic acid, by cell wall sugar composition, and by amino acid composition of the peptidoglycan cell wall layer. The guanine plus cytosine contents of the deoxyribonucleic acids of the isolates were 53 ± 0.46 mol%. Glucose was the principal cell wall sugar detected in each kidney disease bacterium isolate. The major amino acids detected were alanine, glutamic acid, lysine, and glycine. It is proposed that these organisms form a single species belonging to a new genus, for which the name Renibacterium is proposed. The type species is Renibacterium, salmoninarum sp. nov., of which the type strain is Lea-1-74 (= ATCC 33209). This organism is most closely related to the Coryneform Group of Bacteria.
TL;DR: This chapter reviews information on the ecology and diversity of microorganisms that oxidize reduced one-carbon compounds and the types of intracytoplasmic membrane structures found in methylotrophs.
Abstract: Publisher Summary This chapter reviews information on the ecology and diversity of microorganisms that oxidize reduced one-carbon compounds. The presence of methane-oxidizing bacteria in nature has been determined by colony counts and by measurements of methane oxidation. The types of intracytoplasmic membrane structures found in methylotrophs have been subdivided into two basic types. Type I bacteria contains bundles of disk-shaped membrane vesicles distributed throughout the cell. Type II bacteria contain a system of paired membranes throughout the cell or concentrated at the periphery. Facultative methylotrophs that use methanol as a carbon and energy source and assimilate formaldehyde via the serine pathway can be divided into those that use the glyoxylate cycle to regenerate the one-carbon acceptor molecule from acetyl-CoA, and those that lack isocitrate lyase (Icl). The development of a transformation system in M. organophilum has aided in mapping mutants that are deficient in enzymes uniquely involved in one-carbon metabolism, methanol dehydrogenase, formaldehyde dehydrogenase, serine-glyoxalate aminotransferase, hydroxypyruvate reductase, glycerate kinase, and a glyoxalate activated serine transhydroxymethylase.
TL;DR: The penicilllin-binding proteins of several gram-positive and gram-negative bacteria have been examined and it is indicated that there is a wide variation in both the number and the amount of PBPs in different bacteria, and taxonomically related bacteria tend to have similar PBP patterns.
Abstract: The penicilllin-binding proteins (PBPs) of several gram-positive and gram-negative bacteria have been examined. The results indicate that: (i) PBPs are membrane proteins with molecular weights ranging from 40,000 to 120,000. When extracted with Triton X-100 from sonicated cells, they appear to fall into two patterns: one found in rods and the other in spheres. A major difference is in the low-molecular-weight component, which is usually the major PBP in bacilli but a minor one in cocci. (ii) There is a wide variation in both the number and the amount of PBPs in different bacteria, and taxonomically related bacteria tend to have similar PBP patterns. These patterns often correlate with the affinity of PBPs for penicillin and other beta-lactam antibiotics. (iii) The low-molecular-weight component usually releases penicillin spontaneously with a half-life of 10 min or less. Most, but not all, PBPs release bound penicillin in the presence of neutral hydroxylamine (0.2 to 0.8 M).
TL;DR: It appears that the structure (and, presumably, the function) of the heat-modifiable protein of gram-negative bacteria is strongly conserved during evolution.
Abstract: The outer membranes of several strains of Escherichia coli, other enteric bacteria, and a variety of nonenteric gram-negative bacteria all contain a major heat-modifiable protein similar to the OmpA protein of E. coli K-12. The heat-modifiable proteins from these bacteria resemble the K-12 protein in molecular weight, in preferential release from the outer membrane by sodium dodecyl sulfate in the presence of Mg2+, and in characteristic cleavage by proteases to yield a smaller fragment which remains membrane bound. Antiserum directed against the K-12 protein precipitated the heat-modifiable protein from all strains of Enterobacteriaceae, and chemical comparison by isoelectric focusing, cyanogen bromide cleavage profiles, and proteolytic peptide analysis indicated that the proteins from the various enteric bacteria were nearly identical in primary structure. The heat-modifiable proteins from bacteria phylogenically distant from E. coli shared many of the properties of the E. coli protein but were chemically distinct. Thus, it appears that the structure (and, presumably, the function) of the heat-modifiable protein of gram-negative bacteria is strongly conserved during evolution.
TL;DR: It is suggested that bacterial sensitivity or resistance to these purified bactericidal PMN proteins is determined by the binding properties of the outer membrane, which in turn depends upon the LPS-saccharide chain length.
Abstract: The sensitivity or resistance of gram-negative bacteria to antibacterial systems appears to be related to the length of the saccharide chain of the bacterial envelope lipopolysaccharides (LPS). To explore this relationship further, we made use of two bactericidal, membrane-active cationic proteins, recently purified to near homogeneity, one from human and one from rabbit polymorphonuclear leukocytes (PMN). We have studied the effects of these two closely similar proteins on strains of Salmonella typhimurium and Escherichia coli, each separate strain differing in the saccharide chain length of its outer membrane LPS. Binding of these proteins to the bacterial outer membrane is required for killing, and is accompanied by an almost immediate increase in outer membrane permeability to normally impermeant actinomycin D. Sensitivity to the bactericidal and permeability-increasing activities of the human and rabbit proteins increases with decreasing LPS-saccharide chain length (chemotype: [S < Ra < Rb(3) < Rc < Rd(1)]). S. typhimurium G-30 and E. coli J5, mutant strains lacking UDP-galactose-4-epimerase, synthesize incomplete LPS (chemotype Rc) when grown without galactose, and are then as sensitive to both PMN proteins as the S. typhimurium strains 395 R10 (Rd(1)) and R5 (Rb(3)). However, when these mutants are grown with galactose, they synthesize complete LPS (chemotype S) and exhibit nearly the same relative insensitivity as the smooth strains S. typhimurium 395 MS and E. coli 0111:B4. The differences among strains in sensitivity to the effects of the proteins on bacterial viability and permeability correspond to differences in bacterial binding of these PMN proteins. Thus, at protein concentrations that produce maximal antibacterial activity toward the rough bacteria, but little or no activity toward the smooth strains, rough bacteria bind from 3- to 10-fold more protein (S. typhimurium 395 R10; S. typhimurium G-30, and E. coli J5 [grown without galactose]) than do the smooth bacteria (S. typhimurium 395 MS; E. coli 0111:B4; S. typhimurium G-30 and E. coli J5 [grown with galactose]). These findings suggest that bacterial sensitivity or resistance to these purified bactericidal PMN proteins is determined by the binding properties of the outer membrane, which in turn depends upon the LPS-saccharide chain length.
TL;DR: Ammonium-oxidizing bacteria were examined in two wetland environments, a freshwater marsh and an estuarine bay, during a 2-year period, suggesting that the organism is a trueEstuarine bacterium.
Abstract: Ammonium-oxidizing bacteria were examined in two wetland environments, a freshwater marsh and an estuarine bay, during a 2-year period. Two predominant types were consistently isolated, one from each environment. Both isolates were identified as species ofNitrosomonas. Using a closed culture, high cell density assay, the effects of temperature, pH, salinity, Na(+), K(+), nitrite, nitrate, and ammonium concentrations on ammonium oxidation were determined. Maximum activity was observed for the freshwater isolate at 35°C, pH 8.5, salinities of 0.3 to 0.5% Na(+) and K(+), and ammonium concentrations greater than 0.5 g/l. For the estuarine isolate, maximum activity was observed at 40°C, pH 8.0, salinities of 0.5 to 1.0%, 1.0% Na(+) and K(+), and 0.2 g/l ammonium. The estuarine isolate had a Na(+) requirement which could be partially substituted by the K(+), suggesting that the organism is a true estuarine bacterium. Nitrite inhibited both isolates at concentrations greater than 5 mg/l, whereas nitrate had no significant effect on either isolate.
TL;DR: Both decreased uptake and increased efflux of tetracycline occurred in resistant strains under conditions where bacteria were still metabolically functional.
TL;DR: A strain of Streptomyces, isolated from a soil sample, has been found to produce FR-900098, an interesting new antibiotic containing phosphorus in its molecule, which was shown to inhibit a wide variety of Gram-negative bacteria including Pseudomonas, Proteus, and Escherichia coli.
Abstract: A strain of Streptomyces, isolated from a soil sample and identified as Streptomyces rubellomurinus sp. nov., has been found to produce FR-900098, an interesting new antibiotic containing phosphorus in its molecule. The antibiotic, obtained as colorless crystals, was shown to inhibit a wide variety of Gram-negative bacteria including Pseudomonas, Proteus, and Escherichia coli. Its antibacterial action involves interference with bacterial cell wall synthesis as evidenced by the fact that it causes spheroplast formation by susceptible cells.
TL;DR: At all stages of the digestion of intact legume leaves, the rumen bacteria grew in microcolonies composed of cells of single or mixed morphological types, and a particular ecological niche was often completely and consistently occupied by a very large microcolony of cells that produced very extensive exopolysaccharide-enclosedmicrocolonies.
Abstract: When fresh whole leaves of six different species of forage legumes were suspended in an artificial rumen medium and inoculated with rumen bacteria, bacterial adhesion and proliferation were noted at the stomata, and penetration of the stomate by these bacteria was documented by electron microscopy. The invading bacteria adhered to surfaces within the intercellular space of the leaf and produced very extensive exopolysaccharide-enclosed microcolonies. After some of the legume leaf cell walls were disorganized and ruptured by bacterial digestion, these cells (notably, parenchyma and epidermal cells) were invaded by bacteria, with subsequent formation of intracellular microcolonies. However, other cells were neither ruptured nor colonized (notably, stomata guard cells and vascular tissue). At all stages of the digestion of intact legume leaves, the rumen bacteria grew in microcolonies composed of cells of single or mixed morphological types, and a particular ecological niche was often completely and consistently occupied by a very large microcolony of cells of single or mixed morphological types. Images
TL;DR: Obligately anaerobic oxalate-degrading bacteria were isolated from an enriched population of rumen bacteria in an oxalating medium that had been depleted of other readily metabolized substrates.
Abstract: Obligately anaerobic oxalate-degrading bacteria were isolated from an enriched population of rumen bacteria in an oxalate-containing medium that had been depleted of other readily metabolized substrates These organisms, which are the first reported anaerobic oxalate degraders isolated from the rumen, were gram negative, nonmotile rods They grew in a medium containing sodium oxalate, yeast extract, cysteine, and minerals The only substrate that supported growth was oxalate Growth was directly related to the concentration of oxalate in the medium (1 to 111 mM), and cell yields were approximately 11 g (dry weight)/mol of oxalate degraded Oxalate was stoichiometrically degraded to CO2 and formate These anaerobes occupy a unique ecological niche and are distinct from any previously described oxalate-degrading bacteria
TL;DR: Two "rickettsia-like organisms," TATLOCK and HEBA, isolated from human blood via guinea pigs and embryonated eggs in 1943 and 1959, respectively, have been cultured on artificial media for the first time and characterized.
Abstract: Two "rickettsia-like organisms," TATLOCK and HEBA, isolated from human blood via guinea pigs and embryonated eggs in 1943 and 1959, respectively, have been cultured on artificial media (charcoal yeast extract agar) for the first time and characterized. TATLOCK and HEBA have identical cultural, biochemical, and antigenic characteristics, as well as identical cellular fatty-acid composition and antimicrobial susceptibilities. These two bacteria have most of the cultural and biochemical characteristics of Legionella pneumophilia, and their gas-liquid chromatography cellular fatty-acid profile is similar to that of WIGA, another bacterium similar to L. pneumophila. Direct fluorescent-antibody reagents prepared for HEBA and TATLOCK gave equal high-titered reciprocal staining and were negative on 220 other bacteria, including L. pneumophila. Deoxyribonucleic acid relatedness studies, however, showed that these bacteria are not genetically related to either L. pneumophila or the WIGA bacterium.
TL;DR: Sea urchins have the ability to digest cellulose, probably with the aid of the gut flora, and intestinal microorganisms can synthesize essential amino acids; and amino acids of microbial origin are available to the sea urchin.
Abstract: The gut of the sea urchin Strongylocentrotus droebachiensis has between 2 × 108 and 6 × 109 bacteria/mL of gut contents. When these bacteria are present, radioactive carbon fed to the urchins as ei...
TL;DR: Differences in chemical structure were shown to cause major and selective changes in the affinities of the beta-lactams for the PBPs Only 4 of the 28 compounds tested induced a specific morphological effect (enlargement of the equatorial region) under the particular conditions tested.
Abstract: The interactions of several beta-lactam antibiotics with the penicillin-binding proteins (PBPs) of Streptococcus pneumoniae have been studied using whole organisms treated with such antibiotics and subsequently with [3H]benzylpenicillin. Differences in chemical structure were shown to cause major and selective changes in the affinities of the beta-lactams for the PBPs Only 4 of the 28 compounds tested induced a specific morphological effect (enlargement of the equatorial region) under the particular conditions tested. In 12 of the 18 beta-lactams studied, a close correlation was found between the minimal inhibitory concentrations and the concentrations required to half-saturate PBP2b. However, such a correlation was no longer apparent when the bacteria were treated with the antibiotics at their minimal inhibitory concentrations. These findings are discussed in the context of various approaches that have been used to identify the growth-inhibitory targets of beta-lactam antibiotics in bacteria.
TL;DR: In this article, the authors assessed the interaction of two strains of E. coli at different phases of growth with a monolayer of mouse peritoneal macrophages and developed a direct method with [14C]mannan to quantitate the bacterial mannose-binding activity.
Abstract: Recently, it was suggested that a mannose-specific lectin on the bacterial cell surface is responsible for the recognition by phagocytic cells of certain nonopsonized Escherichia coli strains. In this study we assessed the interaction of two strains of E. coli at different phases of growth with a monolayer of mouse peritoneal macrophages and developed a direct method with [14C]mannan to quantitate the bacterial mannose-binding activity. Normal-sized bacteria were obtained from logarithmic and stationary phases of growth. Nonseptated filamentous cells were formed by growing the organisms in the presence of cephalexin or at a restrictive temperature. Attachment to macrophages of all bacterial forms was inhibited by methyl α-d-mannoside and mannan but not by other sugars tested. The attachment of stationary phase and filamentous bacteria to macrophages, as well as their mannose-binding activity, was similar, whereas in the exponential-phase bacteria they were markedly reduced. The results show a linear relation between the two parameters (R = 0.98, P
TL;DR: Mixed human faecal flora was able to interconvert estrone and estradiol both in aerobic and anaerobic conditions and the significance of these results is discussed in the light of present knowledge of estrogen metabolism.
TL;DR: A close correlation was observed between the ability to induce SCEs or chromosomal aberrations and the mutagenic potency in bacteria and the results from microbial reversion assays.
Abstract: The induction of sister-chromatid exchanges (SCEs), chromosomal aberrations and polyploids was investigated in cultured Chinese hamster cells treated with pesticides or a related compound positive in microbial reversion assays. The chemicals tested were captan, captafol, 1,2-dibromoethane (EDB), 1,2-dibromo-3-chloropropane (DBCP), 5-nitro-1-naphrhonitrile (NNN), p-dimethylaminobenzenediazo sodium sulfonate (DAPA), 2-hydrazinoethanol (HEH), vamidothion, dichlorovos (DDVP), N-nitroso-ethylenethiourea (N-nitroso-ETU), and 2,4-dinitrophenyl thiocyanate (NBT). A significant and dose-dependent increase in the frequency of SCEs and chromosomal aberrations was observed in the cell cultures treated with captan, captafol, EDB, DBCP, HEH, DDVP, vamidothion, DAPA or N-nitroso-ETU or NBT produced a significant increase in the frequency of polyploid cells, whereas the other agents did not. When compared with results from microbial reversion assays, a close correlation was observed between the ability to induce SCEs or chromosomal aberrations and the mutagenic potency in bacteria (r:0.71-0.84).