The co-induction of sister chromatid exchanges and virus synthesis in mammalian cells

Evaluation of cytogenetic effects of a naturally occurring non-ice-nucleation Pseudomonas fluorescens strain in Chinese hamster ovary (CHO) cells

One of the main methods for eliminating ice-nucleation-active (INA+) bacteria the micro-organisms responsible for frost injuries to plants at mild freezing temperatures, is the use, as competitors, of other naturally occurring non-nucleating strains (non-INA). In the present article we investigated the cytogenetic effects of a naturally occurring non-INA strain of Pseudomonas fluorescens (MS 1640 R3), evaluating the induction of chromosomal aberrations and sister chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) cells in the absence and presence of rat S9 metabolism. The results obtained did not show any increase in either chromosomal aberrations or SCEs, both in the absence and presence of rat S9 metabolism when used as i) intact bacteria cells, ii) sonicated bacteria (i.e., potential endotoxins), or iii) metabolic bacterial products (i.e., potential exotoxins) released in the growth medium.

Cytogenetic study for possible mutagenic activity induced by ice-nucleation bacteria or their metabolic products in human lymphocytes in vitro

A means for eliminating ice-nucleation-active (INA) bacteria, the microorganisms responsible for frost damage to plants at mild freezing temperatures, is the use as competitors of other naturally occurring, non-nucleating strains. Inactive mutants (INA-) of INA bacteria have been produced by genetic or chemical methods and proposed for biological control of INA populations. Since, however, the application of these INA- mutants in the field may create health hazards to animals, we have studied the possible mutagenic activity of the INA- mutants by examining chromosome aberrations, sister-chromatid exchange (SCE) frequencies, and proliferation kinetics of human lymphocyte cultures. These cultures were treated with: (a) a naturally occurring INA- bacterium (p 767), (b) 2 parental strains (cit 7 and cit 13) of INA bacteria isolated from Citrus orchards, and (c) 2 INA- mutant strains (cit 7 del 1b and cit 13-12), produced, respectively, by chemical modification and by deletion of the corresponding parental strains. Neither whole bacteria nor infiltrates of bacterial growth media, in which toxic metabolic bacterial products might have been released, induced elevation of either chromosome aberrations and SCEs or a cell-division delay. Negative results were also obtained when sonicated bacteria were tested for possible intracellular mutagenic components.

Sister chromatid exchanges and chromosomal aberrations induced by mitomycin C in mouse lymphocytes carrying a leukemogenic virus

The induction of chromosomal damage (sister chromatid exchanges (SCEs), chromosomal aberrations, and micronuclei) in T lymphocytes from mouse spleen was analyzed after treatment in vivo with different concentrations of mitomycin C (MMC). Lymphocytes were derived from BALB/Mo mice, which carry an endogenous type C retrovirus (Moloney murine leukemia virus, M-MuLV), and from BALB/c mice (controls, M-MuLV-free). Chromosomal damage was determined in vitro on lymphocytes stimulated with concanavalin A (Con A) and incubated for two generation cycles with bromodeoxyuridine (BUdR). The baseline frequency of SCEs was significantly higher in untreated BALB/Mo than in BALB/c lymphocytes. The frequencies of SCEs were significantly increased by increasing doses of MMC in both BALB/c and BALB/Mo T lymphocytes. Treatment with a low dose of MMC (0.3 mg/kg) produced an additive effect on SCE frequency in BALB/Mo lymphocytes, which was gradually suppressed by increasing the MMC concentration (3-5 mg/kg). Indeed, the levels of SCEs became significantly lower in BALB/Mo than in BALB/c lymphocytes at the highest MMC concentration tested (10 mg/kg), indicating that a negative synergistic effect was eventually produced. Chromosomal aberrations (breaks and total aberrations) were significantly increased by the highest MMC doses (5-10 mg/kg) and were more frequent in BALB/Mo than in BALB/c lymphocytes at 10 mg/kg MMC. The frequencies of micronuclei were increased by all MMC doses and were significantly higher in BALB/Mo than in BALB/c lymphocytes at 10 mg/kg MMC. These results are referred to interferences of M-MuLV and MMC with the function of enzymes, such as DNA topoisomerases, involved in the mechanism of SCE production.

The longevity of chemically induced sister chromatid exchanges in Chinese hamster ovary cells

The persistence of the lesions leading to sister chromatid exchanges (SCEs) following acute exposure of Chinese hamster ovary (CHO) cells to direct-acting chemical mutagens was measured. The results revealed that these lesions (and consequently SCEs) are rapidly eliminated from cells. SCE levels fell to near control values by the third or fourth day (six and eight cell cycles, respectively) following exposure of CHO cells to quinacrine mustard (QM) and mitomycin C (MMC). In contrast, cells exposed to methyl methanesulfonate (MMS) showed a small but significant increase in SCE level over control up to and including the fifth day following exposure (approximately ten cell cycles), suggesting that the behavior of these lesions in cells is influenced, at least in part, by the mechanism by which a specific agent interacts with DNA. The possibility that the decline in SCE level was due to the loss of cell populations with high numbers of exchanges was eliminated by the assessment of cloning efficiencies of treated and control cultures.

Sister chromatid exchange (SCE) and structural chromosome aberration in mutagenicity testing

Data from previous studies published on the induction by mutagens of sister chromatid exchanges (SCEs) and structural chromosome damage were compared qualitatively and quantitatively. Although a good correlation between the incidence of both cytogenetic phenomena has been pointed out in many previous publications, about 30% of the agents for which comparable data were available yielded non-corresponding qualitative results concerning both indicator effects. However, even in groups with good qualitative agreement distinct quantitative differences indicated different molecular mechanisms of the formation of SCEs and breaks. Additional information supporting the importance of these differences for the validity of both indicator systems has been derived from the results obtained using strong clastogens exhibiting a low or no SCE-inducing activity and vice versa, from special observations on chromosomal breakage syndromes, and from studies on the action of known co- and anti-clastogens on SCE-induction by chemical mutagens. As a result, it has been suggested that the SCE-technique should be considered as a valuable additional method for cytogenetic mutagenicity testing, which, however, is not adequate to replace the classical methods of analysis of structural chromosome damage.