Lethal and mutagenic effects of elevated temperature on haploid yeast. II. Recovery from thermolesions

High resistance to oxidative stress in the fungal pathogen Candida glabrata is mediated by a single catalase, Cta1p, and is controlled by the transcription factors Yap1p, Skn7p, Msn2p, and Msn4p

We characterized the oxidative stress response of Candida glabrata to better understand the virulence of this fungal pathogen. C. glabrata could withstand higher concentrations of H(2)O(2) than Saccharomyces cerevisiae and even Candida albicans. Stationary-phase cells were extremely resistant to oxidative stress, and this resistance was dependent on the concerted roles of stress-related transcription factors Yap1p, Skn7p, and Msn4p. We showed that growing cells of C. glabrata were able to adapt to high levels of H(2)O(2) and that this adaptive response was dependent on Yap1p and Skn7p and partially on the general stress transcription factors Msn2p and Msn4p. C. glabrata has a single catalase gene, CTA1, which was absolutely required for resistance to H(2)O(2) in vitro. However, in a mouse model of systemic infection, a strain lacking CTA1 showed no effect on virulence.

Viability of Saccharomyces cerevisiae cells exposed to low-amperage electrolysis as assessed by staining procedure and ATP content

Assessment of yeast viability by plate counts, ATP determination and FUN-1 viability staining was performed to study sublethal injury of Saccharomyces cerevisiae cells submitted to low-amperage electrolysis. Lethal effects of electrolysis were confirmed by all methods, demonstrated by the decrease in viable counts observed during electrolysis. FUN-1 viability staining and ATP determination appeared to demonstrate higher survivors than plate counts. To study possible recovery of certain yeast cells damaged by electrolysis thus rendering them nonculturable, yeast suspensions were stored in phosphate buffer at 4 and 20 degrees C. Increase in viable counts and ATP content of treated yeast cells was observed during storage at 20 degrees C, whereas viable counts of treated and control yeast cells were shown to decrease during storage at 4 degrees C. The increase in the number of viable cells appeared to be the result of repair of damaged cells rather than regrowth of few cells remaining culturable. The lethal efficacy of electrolysis might be overestimated by plate counts. Further experiments must be done to evaluate the lethal efficacy of electrolysis on microorganisms in real conditions encountered in food products.

Heat and UV light resistance of vegetative cells and spores of Bacillus subtilis Rec-mutants

The heat and UV light resistance of spores and vegetative cells of Bacillus subtilis BD170 (rec+) were greater than those of B. subtilis BD224 (recE4). Strain BD170 can repair DNA whereas BD224 is repair deficient due to the presence of the recE4 allele. Spores of a GSY Rec+ strain were more heat resistant than spores of GSY Rec- and Uvr- mutants. The overall level of heat and UV light resistance attained by spores may in part be determined by their ability to repair deoxyribonucleic acid after exposure to these two physical mutagens.

Effect of growth temperature upon heat sensitivity in Saccharomyces cerevisiae

The resistance of exponentially growing yeast cells to killing by exposure to 52 degrees C increase markedly as the growth temperature was increased. Identical killing curves were obtained for cells suspended in growth medium or in 0.9% saline. Cells resistant to killing at 52 degrees C were quite sensitive to killing at slightly higher temperatures. These results suggest a primary role for membrane damage in the mechanism of heat killing.

Mutagenic action of hydrostatic pressure on yeast: a cell cycle analysis

Pressure-treated log growth cultures (14,000 psi equivalent to 966 x 10(5) N/m2 for 4 h) of Saccharomyces cerevisiae were fractionated across a linear Ficoll gradient by zonal rotor centrifugation. This procedure separated the yeast cells on the basis of size and volume into a continuum of cell cycle ages. Cell survival and petite mutation frequency were determined for several zonal fractions. Survival of yeast cells after pressure treatment was maximal in zonal fractions obtained from either the top (single cells in G1) or the botton ("doublets") of the gradient. Intermediate zonal fractions showed more lethality, with minimal survival occurring in zonal fractions containing a large proportion of yeast cells in which buds were just beginning to emerge (initiation of S phase). The petite mutation frequency was minimal in zonal fractions from the top (single cells in G1) and bottom ("doublets") of the gradient. Induction increased to a maximum in those fractions containing cells in S phase.

Protein synthesis and the recovery of both survival and cytoplasmic "petite" mutation in ultraviolet-treated yeast cells. I. Nuclear-directed protein synthesis

The contribution of nuclear-directed protein synthesis in the repair of lethal and mitochondrial genetic damage after UV-irradiation of exponential and stationary phage haploid yeast cells was examined. This was carried out using cycloheximide (CH), a specific inhibitor of nuclear protein synthesis. It appears that nuclear protein synthesis is required for the increase in survival seen after the liquid holding of cells at both stages, as well as for the "petite" recovery seen after the liquid holding of exponential phase cells. The characteristic negative liquid holding effect observed for the UV induction of "petites" in stationary phase cells (increase of the frequency of "petites" during storage) remained following all the treatments which inhibited nuclear protein synthesis. However, the application of photoreactivating light following dark holding with cycloheximide indicates that some steps of the repair of both nuclear and mitochondrial damage are performed in the absence of a synthesis of proteins.