Microorganisms in nature form organized multicellular structures (colonies, biofilms) possessing properties absent in individual cells. These are often related to the better ability of communities to survive long-lasting starvation and stress and include mechanisms of adaptation and cell specialization. Thus, yeast colonies pass through distinct developmental phases characterized by changes in pH and the production of ammonia-signalling molecules. Here, we show that Saccharomyces cerevisiae colony transition between major developmental phases (first acidic, alkali, second acidic) is accompanied by striking transcription changes, while the development within each particular phase is guided mostly at the post-transcriptional level. First- and second-acidic-phase colonies markedly differ. Second-acidic-phase colonies maintain the adaptive metabolism activated in the ammonia-producing period, supplemented by additional changes, which begin after colonies enter the second acidic phase. Cells with particular properties are not homogenously dispersed throughout the colony population, but localize to specific colony regions. Thus, cells located at the colony margin are able to export higher amounts of ammonium than central cells and to activate an adaptive metabolism. In contrast, central chronologically aged cells are unable to undergo these changes but they maintain higher levels of various stress-defence enzymes. These divergent properties of both cell types determine their consequent dissimilar fate.

Volatile ammonia functions as a long range alarm signal important for the transition of yeast colonies to their adaptive alkali developmental phase and for their consequent long term survival. Cells of aged Saccharomyces cerevisiae sok2 colonies deleted in the gene for Sok2p transcription factor are not able to release a sufficient amount of ammonia out of the cells, they are more fragile than cells of wild type colonies, and they exhibit a survival defect. Genome-wide analysis on gene expression differences between sok2 and WT colonies revealed that sok2 colonies are not able to switch on the genes of adaptive metabolisms effectively and display unbalanced expression and activity of various enzymes involved in cell protection against oxidative damage. Impaired amino acid metabolism and insufficient activation of genes for putative ammonium exporters Ato and of those for some other membrane transporters may be responsible for observed defects in ammonia production. Thus, Sok2p appears to be an important regulator of S. cerevisiae colony development. Gene expression differences caused by its absence in colonies differ from those described previously in liquid cultures, which suggests a pleiotropic effect of Sok2p under different conditions.

Over a 12-year period, from 1987 to 1998, the spectrum of aetiological agents isolated from 11208 patients (6265 females and 4943 males) suspected of having dermatomycosis was analysed in the mycological laboratory of the Department of Dermatology, Charles University, Prague. The most frequently examined locations were toenails (34.9%), feet (15.6%), fingernails (12.8%), toe webs (11%), trunk (10%) and hands (8.7%). Dermatophytes were isolated from 5605 (30.2%) of all 18528 samples examined. Among dermatophytes, the most common infectious agent was Trichophyton rubrum (90.2%) followed by Trichophyton mentagrophytes (6.6%), Microsporum canis (1.8%) and Epidermophyton floccosum (1.4%). Trichophyton verrucosum, Microsporum persicolor and Microsporum gypseum were rare. During this 12-year period the pattern of aetiological agents of dermatomycoses in Prague was relatively stable.