Physiological modification of alkylating-agent induced mutagenesis. I. Effect of growth rate and repair capacity on nitrosomethylurea-induced mutation of Escharichia coli.

The effects of repair capacity and growth rate on the induction of mutations by N-methyl-N-nitosourea (MNUA) was investigated using the trpE reversion system of Escherichia coli WP2 and some repair-deficient derivatives isogenic for this gene. In all these strains reducing the growth rate prior to MNUA-treatment caused a reduction in the mutational response, however major differences were observed between strains. In exrA and recA- bacteria stationary phase cells were 100 times less mutable than cells grown at a mean generation time (m.g.t.) of 30 min, whereas reductions of 12 and 25 times were observed in the uvrA- and wild-type strains respectively. In contrast the mutational response of the polA- mutant varied only slightly with growth rate; the increases at high MNUA concentrations being equal to the increase in the trpE gene number. These results show the increasing importance of the error-prone exrA+/recA+-dependent repair system in mutation-induction by MNUA as the growth rate of the culture is reduced and its relative unimportance for mutation induction in nutrient broth-grown cells (m.g.t. 30 min).

[The epidemiology of gastric cancer (author's transl)]. / Epidemiologie des Magenkarzinoms

Gastric cancer is a highly fatal, common form of cancer in many countries and its medical, surgical, radiologic or combined treatment is very problematic. Thus, a search for its cause and prevention may be more promising than a search for its cure. Epidemiologic data from international studies suggest that environmental factors are more influential than genetic ones in the pathogenesis of gastric cancer, although its causes have not yet been identified. It is likely that the disease has a multi-factorial pathogenesis and that an ingested carcinogen may exert its influence at a time of enhanced susceptibility (damaged mucosa, older age, etc.), particulary in individuals with inherent, elevated risk (males, selected hereditary background etc.). In general, dietary studies have been less rewarding than occupational and geographic-pathologic analyses; such investigations may eventually identify the crude sources of carcinogens which then can be isolated by chemical means.