Information about the functions of extracellular autoregulators, which adapt microorganisms to the stresses “scheduled” in the development cycle of microbial cultures (stresses of new medium, starvation, or space exhaustion (high cell density)) is summarized in the review. In a number of bacteria and yeasts, derivatives of alkylhydroxybenzenes (AHB), particularly of the class of alkyl resorcinols, act as autoregulators with adaptogenic functions. The chemical structure of AHB determines their amphiphility; capacity for physical and chemical interaction with membrane lipids, proteins, and DNA; properties as natural modifiers of biological membranes and enzymes; and the expression of antioxidant activity. Increase of AHB concentration up to the critical level (10⁻⁵-10⁻⁴ M) results in cessation of cell division and in transition of the microbial culture to the stationary phase; further increase to 10⁻⁴-10⁻³ M induces a transition of some of the cells of a post-stationary culture to the anabiotic state with the formation of cystlike resting cells (CRC), even in non-spore-forming bacteria. AHB participate in the regulation of the phenotypic variability of bacteria. The dynamics of extra-and intracellular concentrations of AHB in growing microbial cultures and the polymodality of their effect determine the adaptogenic functions of AHB as autoinhibitors of culture growth, autoinducers of anabiosis, and autoinhibitors of germination of resting forms. Manifestation of any given function depends on the concentration of AHB, the physiological state of the recipient cells, and on environmental factors. The species nonspecificity of AHB effects points to their significant role in the regulation of the development and functioning of microbial communities.

A thermotolerant, Gram-positive, aerobic, endospore-forming, acidophilic bacterium (strain Kr1^T) was isolated from the pulp of a gold-containing sulfide concentrate processed at 40 °C in a gold-recovery plant (Siberia). Cells of strain Kr1^T were straight to slightly curved rods, 0.8–1.2 μm in diameter and 1.5–4.5 μm in length. Strain Kr1^T formed spherical and oval, refractile, subterminally located endospores. The temperature range for growth was 20–60 °C, with an optimum at 40 °C. The pH range for growth on medium containing ferrous iron was 1.2–2.4, with an optimum at pH 2.0; the pH range for growth on medium containing S⁰ was 2.0–5.0, with an optimum at pH 2.5. Strain Kr1^T was mixotrophic, oxidizing ferrous iron, S⁰, tetrathionate or sulfide minerals as energy sources in the presence of 0.02 % yeast extract or other organic substrates. The G+C content of the DNA of strain Kr1^T was 48.2±0.5 mol%. Strain Kr1^T showed a low level of DNA–DNA reassociation with the known Sulfobacillus species (11–44 %). 16S rRNA gene sequence analysis revealed that Kr1^T formed a separate phylogenetic group with a high degree of similarity between the nucleotide sequences (98.3–99.6 %) and 100 % bootstrap support within the phylogenetic Sulfobacillus cluster. On the basis of its physiological properties and the results of phylogenetic analyses, strain Kr1^T can be affiliated to a novel species of the genus Sulfobacillus, for which the name Sulfobacillus thermotolerans sp. nov. is proposed. The type strain is Kr1^T (=VKM B-2339^T=DSM 17362^T).

Cultivation of Mycobacterium smegmatis cells in a nitrogen-limited minimal medium (SR-1) followed by prolonged storage at room temperature without shaking resulted in the gradual accumulation of morphologically distinct ovoid forms characterized by (i) low metabolic activity; (ii) elevated resistance to antibiotics and to heat treatment; and (iii) inability to produce colonies on standard agar plates (non-platable cells). Detailed microscopic examination confirmed that ovoid cells possessed an intact cell envelope, specific fine structure and large electron-transparent bodies in the cytoplasm. Cell staining with Nile red and analysis of the lipid content by TLC revealed the presence of significant amounts of apolar lipids in these bodies. The ovoid forms could be stored for significant periods (up to 5 months) and resuscitated afterwards in a modified Sauton's medium. Importantly, resuscitation of ovoid cells was accompanied by their transformation into the typical rod-shaped cells. We suggest that the observed ovoid cells represent dormant forms, resembling morphologically distinct cells of Mycobacterium tuberculosis previously isolated from tuberculosis patients and infected animals.

Ultramicrobacteria (UMB) are species of the domain Bacteria characterized by very small sizes of proliferating cells (less than 0.1 μm³ in volume) and small genomes (3.2 to 0.58 Mb). Some authors use the term nanobacteria as a synonym of UMB. Several tens of UMB species have been isolated from various natural habitats: sea water, soil, silt, Greenland ice sheet, permafrost soils, and intestines of humans and insects. Under laboratory conditions, they are cultivated on different nutrient media. In the second prokaryotic domain, the Archaea, ultrasmall forms (ultramicroarchaea) have also been described, including nanoarchaea (members of the genus Nanoarchaeum) with a cell volume of less than 0.1 μm³. The term nanobacteria is used in the literature also to denote ultrasmall bacterium-like particles occurring in rocks, sands, soils, deep sub-surface layers, meteorites, and clinical samples. The systematic position and the capacity for self-reproduction of these particles are still unclear. The cultured UMB forms are characterized by highly diverse morphology, ultrastructural organization, physiology, biochemistry, and ecology. UMB form three groups according to the type of cell wall structure and the reaction to Gram staining: (1) gram-negative, (2) gram-positive, and (3) cell wall-lacking. Their cells divide by constriction, septation, or budding. The unique processes performed by UMB are dehalorespiration and obligate or facultative epibiotic parasitism. The UMB that synthesize organic compounds in ocean waters with the involvement of proteorhodopsin play a great role in the biosphere. UMB have been found in seven large phylogenetic groups of prokaryotes, where their closest relatives are organisms with larger cells typical of bacteria, which is evidence of the polyphyletic origin of the currently known UMB species and the reductive mode of their evolution.