19196279 OR Metabolic diversification of cells during the development of yeast colonies Dotaz Zobrazit nápovědu
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.
Yeast populations can undergo diversification during their growth and ageing, leading to the formation of different cell-types. Differentiation into two major subpopulations, differing in cell size and density and exhibiting distinct physiological and metabolic properties, was described in planktonic liquid cultures and in populations of colonies growing on semisolid surfaces. Here, we compare stress resistance, metabolism and expression of marker genes in seven differentiated cell subpopulations emerging during cultivation in liquid fermentative or respiratory media and during colony development on the same type of solid media. The results show that the more-dense cell subpopulations are more stress resistant than the less-dense subpopulations under all cultivation conditions tested. On the other hand, respiratory capacity, enzymatic activities and marker gene expression differed more between subpopulations. These characteristics are more influenced by the lifestyle of the population (colony vs. planktonic cultivation) and the medium composition. Only in the population growing in liquid respiratory medium, two subpopulations do not form as in the other conditions tested, but all cells exhibit a range of characteristics of the more-dense subpopulations. This suggests that signals for cell differentiation may be triggered by prior metabolic reprogramming or by an unknown signal from the structured environment in the colony.
