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PubMed1979

Genetic exchanges in the macrocysts of Dictyostelium discoideum.

Crosses were made between strains of Dictyostelium discoideum involving two drug resistance markers and the mating-type locus. Over 6000 progeny from 263 individual germinated macrocysts from four single-factor crosses, five two-factor crosses and one three-factor cross were characterized. In most cases the progeny from a single macrocyst were of one genotype, although in the population of macrocysts from any two-factor cross all possible parental and recombinant genotypes were recovered. There was no evidence of linkage between any of the markers examined. No selection against progeny carrying the methanol or the cycloheximide resistance markers was found in two-factor crosses, but selection against progeny carrying both resistance markers was found in the three-factor cross. Germination of macrocysts in all crosses was poor, only once exceeding 2.5% of the total macrocyst population. A variety of crosses and back-crosses with different parental strains indicated that germination might be influenced by both extrinsic (environmental) and multiple genetic factors. About 10% of the macrocysts yielded progeny spores that were ambivalent in their mating reactions. After extensive recloning these populations could be resolved to the normal matA (formerly A1) and mata (formerly A2) mating-types and might therefore have represented aneuploids. The results obtained with D. discoideum macrocysts differ from those obtained with other cellular slime moulds--Dictyostelium mucoroides, Dictyostelium giganteum and Polysphondylium pallidum--and are reminiscent of the results reported for germinated zygospores of Phycomyces blakesleeanus.

Crosses, Genetic↗
PubMed1970

Fitness of an Escherichia coli mutator gene.

Competition experiments between Escherichia coli mutT1 and mut(+) populations show that the mutator gene confers selective advantage on the strain that carries it. The observed increase in fitness varies, with an average increase in mutator growth rate of 1.4 percent when mutator and wild-type strains are grown together in chemostats.

DNA Replication↗
PubMed1972

Epidemiological differentiation of Serratia marcescens: typing by bacteriocin production.

A new method for comparing and differentiating strains of S. marcescens is described which has proved useful in determining the epidemiology of hospital infections. Strains were grown in Trypticase soy broth, and bacteriocin production was induced with mitomycin C for 5 hr. The bacteriocin lysates were then spotted onto nine standard indicator strains, which were chosen with the aid of computer analysis from the 118 indicators tested. After 24 hr at 37 C, zones of inhibition due to bacteriocins were recorded. One hundred twentynine strains were differentiated into 72 different bacteriocin production patterns, but 11 strains were nontypable. None of the 45 other strains of Enterobacteriaceae produced bacteriocins. Bacteriocin production was a stable epidemiological marker. Colonial mutants always had identical patterns, as did the same strain which has passed from patient to patient through cross-infection. The new technique does not require any specialized equipment and can be used in laboratories with limited budgets. The applications of the new method in cross-infection studies and as a supplement to serological typing are discussed.

Bacteriocins↗
PubMed1972

Initiation of dermatophyte pleomorphic strain sporulation by increased aeration.

A normally asporogenous pleomorphic strain of Microsporum gypseum was induced to sporulate by controlled aeration and dehydration. Aeration of the pleomorphic strain under optimal cultivation conditions caused the initiation of a sporulation cycle with equivalent growth parameters and percentage intracellular water loss as the wild-type strain. Initiation of sporulation was not due to alteration of the medium's nutrient concentration or consistency, concentration of fungal growth by-products, or removal of volatile "staling factors." Macroconidia formed by the pleomorphic colonies were of characteristic wildtype morphology, but germinated to form typical pleomorphic colonies, indicating that the induced sporulation was strictly phenotypic and reversible. Other asporogenous pleomorphic strains from different dermatophyte genera also were induced to form macroconidia by aeration, suggesting a similarity in sporulation induction in Microsporum sp., Epidermophyton floccosum, and Trichophyton violaceum. Initiation of sporulation by aeration further suggested that the pleomorphic mutation was one which affected the sensitivity of the pleomorphic aerial hyphae to natural sporulation inducers (i.e., decreased humidity) and did not represent a loss in the ability to form fertile macroconidia.

Aerobiosis↗