Mitiushina La

Bio: Mitiushina La is an academic researcher. The author has contributed to research in topics: Autolysis (biology) & Methylococcus capsulatus. The author has an hindex of 1, co-authored 1 publications receiving 17 citations.

Formation of resting cells in microbial suspensions undergoing autolysis

Abstract: 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.

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

Abstract: 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.

Production of Dormant Stages and Stress Resistance of Polar Cyanobacteria

Abstract: 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.

Comparative Study of the Elemental Composition of Vegetative and Resting Microbial Cells

Abstract: X-ray microanalysis showed that vegetative cells, viable resting forms, and nonviable forms (micromummies) of the bacteria Bacillus cereus and Micrococcus luteus and the yeast Saccharomyces cerevisiae differ in the content of elements S, P, Ca, and K and Ca/K and P/S ratios. Viable resting forms (cystlike refractive cells and bacillar endospores) had more calcium and less phosphorus and potassium than vegetative cells, the difference being higher for bacilli than for micrococci and yeasts. The distinctive feature of all viable resting microbial forms was their low P/S ratios and high Ca/K ratios. The differences revealed in the cellular content and ratios of elements probably reflect changes in ionic homeostasis accompanying the transition of vegetative microbial cells to the dormant state. Relevant potassium parameters indicate that the membranes of viable resting forms retain their barrier function. At the same time, the nonviable micromummies, even those morphologically intact, of B. cereus and S. cerevisiae exhibited an anomalously low content of potassium, while those of M. luteus had an anomalously high content of this element. This suggests that the cellular membranes of micromummies lose their barrier function, which results in a free diffusion of potassium ions across the membranes. The possibility of using the elemental composition parameters for the quick analysis of the physiological state of microorganisms in natural environments is discussed.

Study of ultramicrobacteria (Nanoforms) in soils and subsoil deposits by electron microscopy

Abstract: The use of multiple centrifuging and filtration of water suspensions from different soils and subsoil deposits allowed revealing the ultrafine forms (nanosized, nanoforms) of bacteria. In the soils studied, the number of bacteria obtained by filtration using 0.2-μm filters was 20–300 mln cells in 1 g soil; the share of these bacteria of their total population in the natural soils reached 5% and was higher (up to 15%) in the polluted urban soils. The study of bacterial nanoforms in situ by the methods of scanning and transmission microscopy has shown the presence of dividing cells, which testifies to their viability. The cells without signs of division were similar in their ultrastructural characteristics to dormant forms of nonspore-forming bacteria. They were observed in permafrost deposits. The data obtained attest that the bacterial nanoforms are widespread in soils and subsoil deposits. According to their morphological and cytological characteristics, they are represented by both active and dormant forms to survive unfavorable conditions.