Divergent branches of mitochondrial signaling regulate specific genes and the viability of specialized cell types of differentiated yeast colonies.

Mitochondrial retrograde signaling mediates communication from altered mitochondria to the nucleus and is involved in many normal and pathophysiological changes, including cell metabolic reprogramming linked to cancer development and progression in mammals. The major mitochondrial retrograde pathway described in yeast includes three activators, Rtg1p, Rtg2p and Rtg3p, and repressors, Mks1p and Bmh1p/Bmh2p. Using differentiated yeast colonies, we show that Mks1p-Rtg pathway regulation is complex and includes three branches that divergently regulate the properties and fate of three specifically localized cell subpopulations via signals from differently altered mitochondria.

SUN family proteins Sun4p, Uth1p and Sim1p are secreted from Saccharomyces cerevisiae and produced dependently on oxygen level.

The SUN family is comprised of proteins that are conserved among various yeasts and fungi, but that are absent in mammals and plants. Although the function(s) of these proteins are mostly unknown, they have been linked to various, often unrelated cellular processes such as those connected to mitochondrial and cell wall functions. Here we show that three of the four Saccharomyces cerevisiae SUN family proteins, Uth1p, Sim1p and Sun4p, are efficiently secreted out of the cells in different growth phases and their production is affected by the level of oxygen.

The transport of carboxylic acids and important role of the Jen1p transporter during the development of yeast colonies.

On solid substrates, yeast colonies pass through distinct developmental phases characterized by the changes in pH of their surroundings from acidic to nearly alkaline and vice versa. At the beginning of the alkali phase colonies start to produce ammonia, which functions as a quorum-sensing molecule inducing the reprogramming of cell metabolism. Such reprogramming includes, among others, the activation of several plasma membrane transporters and is connected with colony differentiation.

Ato protein interactions in yeast plasma membrane revealed by fluorescence lifetime imaging (FLIM).

Each of the three plasma membrane Ato proteins is involved in ammonium signalling and the development of yeast colonies. This suggests that although these proteins are homologous, they do not functionally substitute for each other, but may form a functional complex. Here, we present a detailed combined FRET, FLIM and photobleaching study, which enabled us to detect interactions between Ato proteins found in distinct compartments of yeast cells.

Synchronous plasma membrane electrochemical potential oscillations during yeast colony development and aging.

Microorganisms that survive in natural environments form organized multicellular communities, biofilms and colonies with specific properties. During stress and nutrient limitation, slow growing and senescent cells in such communities retain vital processes by maintaining plasma membrane integrity and retaining the ability to generate transmembrane electrochemical gradients. We report the use of a Saccharomyces cerevisiae colonial model to show that population growth in a multicellular community depends on nutrient diffusion and that resting cells start to accumulate from the beginning of the second acidic phase of colony development.

Putative role for ABC multidrug exporters in yeast quorum sensing.

Pleiotropic drug resistance (PDR) transporters play essential roles in cell resistance to various toxic compounds in various organisms including bacteria, mammals and yeasts. A large group of PDR transporters have been described in yeasts so far, including those that are controlled by transcription factor Pdr1p. Here, we show that besides their role in removing extracellularly added toxic compounds, the Pdr5p and Snq2p transporters play important physiological roles and significantly influence the developmental phases and physiology of yeast populations growing in a liquid culture.

Metabolic diversification of cells during the development of yeast colonies.

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.

Influence of aggregation on interaction of lipophilic, water-insoluble azaphthalocyanines with DOPC vesicles.

Dioleoylphosphatidylcholine unilamellar vesicles made by extrusion technique (LUVETs) were studied as the delivery system for lipophilic water-insoluble potential photosensitizers for photodynamic therapy (PDT). Two azaphthalocyanines (AzaPcs) with hydrophobic substituents only and two also possessing two charged amino groups were introduced into the study. All compounds are insoluble in water and form aggregates in PBS with tetrahydrofuran as cosolvent.

Association of putative ammonium exporters Ato with detergent-resistant compartments of plasma membrane during yeast colony development: pH affects Ato1p localisation in patches.

It was proposed that Ato1p, Ato2p and Ato3p have a role in ammonia production by Saccharomyces cerevisiae colonies (Palkova et al., Mol Biol Cell 13: 3901-3914, 2002). In this study, we show that all three Ato proteins localise to the plasma membrane and their appearance correlates with the beginning of ammonia release.

Sok2p transcription factor is involved in adaptive program relevant for long term survival of Saccharomyces cerevisiae colonies.

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.

External factors involved in the regulation of synthesis of an extracellular proteinase in Bacillus megaterium: effect of temperature.

We studied the effect of temperature on the production of an extracellular neutral metalloproteinase of Bacillus megaterium in a laboratory fermentor under constant aeration and pH. The optimal temperature for growth (35-38° C) was higher than that for the synthesis of proteinase during exponential growth (below 31° C). The critical biomass concentration at which the exponential growth terminated decreased with increase in cultivation temperature.