Tyrosol and farnesol are quorum-sensing molecules produced by Candida albicans which accelerate and block, respectively, the morphological transition from yeasts to hyphae. In this study, we have investigated the secretion of tyrosol by C. albicans and explored its likely role in biofilm development. Both planktonic (suspended) cells and biofilms of four C. albicans strains, including three mutants with defined defects in the Efg 1 and Cph 1 morphogenetic signaling pathways, synthesized extracellular tyrosol during growth at 37°C. There was a correlation between tyrosol production and biomass for both cell types. However, biofilm cells secreted at least 50% more tyrosol than did planktonic cells when tyrosol production was related to cell dry weight. The addition of exogenous farnesol to a wild-type strain inhibited biofilm formation by up to 33% after 48 h. Exogenous tyrosol appeared to have no effect, but scanning electron microscopy revealed that tyrosol stimulated hypha production during the early stages (1 to 6 h) of biofilm development. Experiments involving the simultaneous addition of tyrosol and farnesol at different concentrations suggested that the action of farnesol was dominant, and 48-h biofilms formed in the presence of both compounds consisted almost entirely of yeast cells. When biofilm supernatants were tested for their abilities to inhibit or enhance germ tube formation by planktonic cells, the results indicated that tyrosol activity exceeds that of farnesol after 14 h, but not after 24 h, and that farnesol activity increases significantly during the later stages (48 to 72 h) of biofilm development. Overall, our results support the conclusion that tyrosol acts as a quorum-sensing molecule for biofilms as well as for planktonic cells and that its action is most significant during the early and intermediate stages of biofilm formation.

Production of Tyrosol by Candida albicans Biofilms and Its Role in Quorum Sensing and Biofilm Development

Using electron microscopy (ultrathin sections and freeze-fractures), we investigated the ultrastructure of the resting cells formed in cultures of Micrococcus luteus, Arthrobacter globiformis, and Pseudomonas aurantiaca under conditions of prolonged incubation (up to 9 months). These resting cells included cystlike forms that were characterized by a complex cell structure and the following ultrastructural properties: (i) a thickened or multiprofiled cell wall (CW), typically made up of a layer of the preexisting CW and one to three de novo synthesized murein layers; (ii) a thick, structurally differentiated capsule; (iii) the presence of large intramembrane particles (d = 180–270 A), occurring both on the PF and EF faces of the membrane fractures of M. luteus and A. globiformis; (iv) a peculiar structure of the cytoplasm, which was either fine-grained or lumpy (coarse-grained) in different parts of the cell population; and (v) a condensed nucleoid. Intense formation of cystlike cells occurred in aged (2- to 9-month-old) bacterial cultures grown on diluted complex media or on nitrogen-, carbon-, and phosphorus-limited synthetic media, as well as in cell suspensions incubated in media with sodium silicate. The general morphological properties, ultrastructural organization, and physiological features of cystlike cells formed during the developmental cycle suggest that constitutive dormancy is characteristic of non-spore-forming bacteria.

[Ultrastructure of resting cells of some non-spore-forming bacteria].

Submerged cultures of Arthrobacter globiformis grown in media unbalanced with respect to carbon and nitrogen sources were found to contain cells exhibiting features typical of resting forms: long-term viability, specific ultrastructure, dormant metabolism, and thermoresistance. Such cells were produced not only in the collection strain VKM B-1112, but also in the A. globiformis strains isolated from 2- to 3-million-year-old permafrost sediments.

Reproductive resting forms of Arthrobacter globiformis

Cyanobacteria represent the major component of the autotrophic community in many different types of habitats in both the Arctic and Antarctic. Their dominance is attributed mainly because of their high tolerance to the extreme polar environments. Low temperatures and desiccation are the main forms of physical environmental stressors. During freezing-melting and desiccation periods, the cells are exposed to radical dehydration effects which can be quite damaging. Polar cyanobacteria have evolved a diverse range of protective strategies in order to avoid, or tolerate, the various stresses. The most widespread adaptation to environmental stress is dormancy. Dormancy can be subdivided into diapause and quiescence. Diapause (the cyanobacterial akinete) is endogenously controlled: it is connected to external stressors but is not directly induced by them. Akinetes are more resistant to various insults and commonly considered as overwintering stages. However, the majority of cyanobacteria in the polar regions survive winters without the production of akinetes. This suggests that other alternative mechanisms contribute to survival during stressful conditions. Quiescence (the decrease of metabolic activity under exogenous control) is the transformation into a resistant state, with hardly visible morphological differentiation of the cell. It has been suggested that starvation and entrance into the stationary phase can induce changes in the ultrastructure (e.g., thickening of cell walls) and biochemistry (e.g.,sucrose and trehalose accumulation, changes in composition of fatty acids, secretion of extracellular polysaccharides) of the stressed cells. We accept that the stationary-phase and/or starvation-induced cells can represent alternative dormant stages of polar cyanobacteria which do not produce akinetes. This overview summarizes the present knowledge about production of dormant stages and stress resistance of polar cyanobacteria. It is clear that we still have paucity of information on this topic and that further research is necessary.

Production of Dormant Stages and Stress Resistance of Polar Cyanobacteria

Aerosol deposition of hydroxyapatite and 4-hexylresorcinol coatings on titanium alloys for dental implants.

Under experimentally selected conditions favoring spontaneous or induced autolysis of cell suspensions, the asporogenous bacteria Escherichia coli and Methylococcus capsulatus, the bacilli Bacillus cereus (under conditions of suppressed sporulation), and the yeast Saccharomyces cerevisiae were shown to be capable of forming cystlike resting cells. Their number was influenced by (1) cell density in the suspensions; (2) the presence of Ca2+ ions in nutrient-limited medium; (3) pH of medium; and (4) autolysis rate, dependent on the concentration of oleic acid (a chemical analogue of the autolysis-inducing d2 factor) introduced into the cell suspensions.

Formation of resting cells in microbial suspensions undergoing autolysis

The autoregulatory d1 factor of the yeast, Saccharomyces cerevisiae, that induces the transition of vegetative cells into refractory resting forms, has been isolated from the cell-free culture medium as an individual crystalline compound. It has been shown to be 2-(4-hydroxyphenyl)ethane-1-ol which is also known as tyrosol. When added to the producer culture at 5-15 microM concentration, tyrosol stimulated the endogenous respiration of cells, but inhibited at 20-80 microM concentration. At 200-800 microM concentration, it induced the occurrence of resting forms. The action of tyrosol was not specific, for it also inhibited the cell respiration of the bacteria, Escherichia coli and Bacillus cereus, at 64-86 microM concentration.

[Tyrosol--the autoregulatory d1 factor of the yeast Saccharomyces cerevisiae].

Under certain cultivation conditions, the bacteria Bacillus cereus and Micrococcus luteus form cystlike refractive cells (up to 60% of the total number) that retain viability over a long time, are metabolically inactive and thermotolerant and possess specific ultrastructure. These properties allow them to be attributed to a new type of resting forms of microorganisms.

Griaznova Mn

Papers

Formation of resting cells in microbial suspensions undergoing autolysis

[Tyrosol--the autoregulatory d1 factor of the yeast Saccharomyces cerevisiae].

Formation of a resting form of Bacillus cereus and Micrococcus luteus