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A series of biocide-containing polyethylene composites were obtained using novel guanidine-containing copolymers immobilized on an inert mineral carrier. Multispecies microbial communities were isolated from the surface of polyethylene samples either incubated or found in the environment, and their taxonomic composition was determined. Biofilms reconstructed using microorganisms obtained from different ecotopes were shown to intensively foul polyethylene surfaces. The presence of polyguanidine biocide suppressed the growth and survival of both binary and multispecies biofilms, with a cumulative effect during long-term incubation. When microorganisms were co-cultivated in binary biofilms, the phenomenon of a decrease in biocide effectiveness was demonstrated. This protective effect is potentially based on cooperative interactions inside the binary biofilm community. Scanning electron microscopy showed a pronounced difference in the architecture of reconstructed biofilms incubated in the presence of biocide in comparison to control samples, where biocide suppressed the formation of dense and well-organized three-dimensional structures. Biofilm disruption by immobilized biocides occurred primarily during the later stages of biofilm formation, probably caused by polycation interaction with their negatively charged extracellular components.

This is the first report on the effect of norepinephrine on biofilms and planktonic cultures of a human skin commensal Kytococcus schroeteri H01. A dose-depending inhibitory effect of norepinephrine on K. schroeteri was shown after 24 and 72 h of incubation on PTFE cubes. The most pronounced effect was observed at 3.5 × 10–7 M norepinephrine after 24 h of incubation (71 ± 13% of the control) and at 3.5 × 10–6 M after 72 h (78 ± 10% of the control). Biofilms formed on glass in the presence of norepinephrine were thinner and flatter than in the controls. No significant effect of norepinephrine on metabolic activity of the cells in biofilms formed on PTFE cubes was revealed. Norepinephrine probably affects initial stages of the switching to biofilm lifestyle and matrix synthesis in K. schroeteri H01.

The mechanisms of microbial action on synthetic plastics are analyzed, with the focus on the most widespread polymers produced on an industrial scale. The effect of microbial enzymes on plastic biodegradation and the role of multispecies biofilms in biocorrosion are considered. The main approaches for protection of synthetic plastics from microbially caused damage are discussed.

Patterns of formation of three-species biofilms on the surface of an LDPE-based composite material were studied using a mixture of pure planktonic cultures of microorganisms capable of degrading this polymer. This is the first report of the role of the ascomycete Yarrowia lipolytica as a primary colonizer in this system, forming aggregates with gram-negative bacteria Pseudomonas aeruginosa or Chromobacterium violaceum. Addition of biocidal compounds of the guanidine family to LDPE as a component of the filler was shown to result in selective suppression of biofilm growth of some microorganisms, while it had no effect on the initial stages of adhesion and on planktonic growth of the cultures. Gram-positive bacteria of the genus Kocuria exhibited the highest sensitivity to these biocidal agents.

The impact of steroid hormones, and particularly estradiol, on human microbiota could be recognized as a substantial part of human-microbiota interactions. However, an area that remains poorly investigated is that of the skin and vaginal microbial communities and biofilms, which contain non-pathogenic bacteria of phyla Firmicutes and Actinobacteria, especially probiotic bacteria of the genus Lactobacillus and the widespread, safe skin genus, Micrococcus. Experiments with Lactobacillus paracasei AK508 and Micrococcus luteus C01 biofilms on PTFE cubes showed dose-dependent effects of estradiol at concentrations of 0.22 nM and 22 nM. The hormone mostly inhibits L. paracasei growth and stimulates M. luteus. The presented studies of colony-forming unit (CFU) amountsand cell aggregation in biofilms on glass fiber filters showed the same general tendencies. Estradiol generally increased the aggregation of cells in monospecies communities and potentially changed the synthesis of antibacterial metabolites in L. paracasei. The balance between two bacteria in mixed-species biofilms depended on the initial adhesion stage, and when this stage was reduced, micrococci were more resistant to the antagonistic action of L. paracasei. Moreover, in mixed-species biofilms, the effect of estradiol on lactobacilli altered from inhibition to stimulation, potentially due to the presence of M. luteus. At the same time, ethanol as a solvent for estradiol at the concentration 0.6% acted mostly as an antagonist of the hormone and had an opposite effect on bacteria; nevertheless, the overlapping of ethanol and estradiol effects was shown to be minimal. The data obtained prove the complexity of microbial interactions and the regulatory effect of estradiol on commensal bacteria biofilms.

An express method for measuring biocorrosion of the surface of polyethylene by mono- and multi-species microbial biofilms was developed. The method involves massive inoculation of polyethylene samples with pure microbial cultures or their mixtures, with subsequent incubation for 5‒7 days providing for the biofilm development. The damage to the surface of polyethylene was determined both by the optical method described in this paper and based on measuring the intensity of scattered light and by the standard method using a profilometer. Both methods revealed a direct correlation of the results and may be recommended for practical measurement of the initial stages of biocorrosion of the polyethylene surface. The biocorrosion level was found to depend primarily upon the number of viable microbial cells in the biofilm, rather than upon accumulation of the extracellular polymer matrix.

The concepts on the nature of antibiofilm agents and strategies for their search, which exist in modern literature, are analyzed. A new classification of these compounds is proposed, with subdivision into four major classes depending on their mechanism of action. An advanced system of screening for the pro- and antibiofilm agents is proposed, which will make it possible to improve the efficiency of selection and to expand the spectrum of these compounds.

Binary biofilms containing gram-positive bacteria Micrococcus thailandicus HB or Kocuria rhizophila strain 4A-2G and gram-negative bacteria Escherichia coli strain K-12 or strain ET12567 pRAG56 were obtained. Strain E. coli ET12567 contained a plasmid encoding aminoglycoside phosphotransferase, the enzyme which inactivates kanamycin. A new kinetic approach was developed for selective detection of metabolically active gram-positive bacteria in binary biofilms with E. coli, based on the differences in reduction rate of the electron acceptor, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). It was found that the studied E. coli strains did not exert a protective effect upon the action of antibiotics vancomycin and oxacillin on gram-positive bacteria in the binary biofilms under formation. However, a protective effect was found in the case of preformed binary biofilms: the growth of gram-positive bacteria in binary biofilms was observed at the concentrations of antibiotics oxacillin and kanamycin, which almost completely suppressed growth in the mono-species biofilms of these gram-positive bacteria. The presence of a protective effect was confirmed by several methods (dynamics of MTT reduction, densitometric evaluation of biofilm staining, measurement of the optical density of MTT extracts, and CFU enumeration).

Biofilms are microbial communities of cells embedded in extracellular matrix, and they are regarded as a major form of the natural and laboratory occurrence of bacteria. Cutaneous microbiota is represented by prokaryotic and eukaryotic organisms, which form biofilms in the different niches including the skin surface, glands, and hair follicles. Despite of a large number of in vitro studies dedicated to the biofilms of cutaneous bacteria, the methods used usually do not closely take into account the specific surroundings of certain skin parts. In this study, we introduce a new simple method of biofilm cultivation on the solid keratine/agarose pellets embedded in polyacrylamide gel. In such a model system, we tried to minimize the amount of liquid phase, which makes a model close to a human comedo, and provide a prominent biofilm formation of selected cutaneous bacteria.

The prevention of bacterial biofilm formation is one of the major current challenges in microbiology. Here, by systematically screening a large number of approved drugs for their ability to suppress biofilm formation by Escherichia coli, we identified a number of prospective antibiofilm compounds. We further demonstrated different mechanisms of action for individual compounds, from induction of replicative stress to disbalance of cation homeostasis to inhibition of bacterial attachment to the surface. Our work demonstrates the potential of drug repurposing for the prevention of bacterial biofilm formation and suggests that also for other bacteria, the activity spectrum of antibiofilm compounds is likely to be broad., In most ecosystems, bacteria exist primarily as structured surface-associated biofilms that can be highly tolerant to antibiotics and thus represent an important health issue. Here, we explored drug repurposing as a strategy to identify new antibiofilm compounds, screening over 1,000 compounds from the Prestwick Chemical Library of approved drugs for specific activities that prevent biofilm formation by Escherichia coli. Most growth-inhibiting compounds, which include known antibacterial but also antiviral and other drugs, also reduced biofilm formation. However, we also identified several drugs that were biofilm inhibitory at doses where only a weak effect or no effect on planktonic growth could be observed. The activities of the most specific antibiofilm compounds were further characterized using gene expression analysis, proteomics, and microscopy. We observed that most of these drugs acted by repressing genes responsible for the production of curli, a major component of the E. coli biofilm matrix. This repression apparently occurred through the induction of several different stress responses, including DNA and cell wall damage, and homeostasis of divalent cations, demonstrating that biofilm formation can be inhibited through a variety of molecular mechanisms. One tested drug, tyloxapol, did not affect curli expression or cell growth but instead inhibited biofilm formation by suppressing bacterial attachment to the surface. IMPORTANCE The prevention of bacterial biofilm formation is one of the major current challenges in microbiology. Here, by systematically screening a large number of approved drugs for their ability to suppress biofilm formation by Escherichia coli, we identified a number of prospective antibiofilm compounds. We further demonstrated different mechanisms of action for individual compounds, from induction of replicative stress to disbalance of cation homeostasis to inhibition of bacterial attachment to the surface. Our work demonstrates the potential of drug repurposing for the prevention of bacterial biofilm formation and suggests that also for other bacteria, the activity spectrum of antibiofilm compounds is likely to be broad.

Human natriuretic peptides (NUPs) types A and C were shown have different effects on the growth of monospecies and binary biofilms of human skin commensal microorganisms Staphylococcus epidermidis and Staphylococcus aureus. The effect of natriuretic peptides depended on cultivation conditions: at 37°С growth of monospecies biofilms formed by S. epidermidis and S. aureus was stimulated and inhibited, respectively, resulting in changed values of the biofilm average thickness and biomass in presence of NUPs. At 33°С effects of NUPs reversed: growth of S. epidermidis monospecies biofilms was inhibited. In binary biofilms at 37°С, NUPs were able to increase the competitiveness of S. epidermidis against S. aureus. NUPs affected predominantly biofilms and, to a lesser degree, planktonic cultures. This phenomenon makes it possible to consider NUPs as the molecules able to regulate the interactions between the human organism and skin microbiota.

In this study, the effect of epinephrine on the biofilm formation of Micrococcus luteus C01 isolated from human skin was investigated in depth for the first time. This hormone has a complex effect on biofilms in various systems. In a system with polytetrafluoroethylene (PTFE) cubes, treatment with epinephrine at a physiological concentration of 4.9 × 10−9 M increased the total amount of 72-h biofilm biomass stained with crystal violet and increased the metabolic activity of biofilms, but at higher and lower concentrations, the treatment had no significant effect. On glass fiber filters, treatment with the hormone decreased the number of colony forming units (CFUs) and changed the aggregation but did not affect the metabolic activity of biofilm cells. In glass bottom plates examined by confocal microscopy, epinephrine notably inhibited the growth of biofilms. RNA-seq analysis and RT–PCR demonstrated reproducible upregulation of genes encoding Fe–S cluster assembly factors and cyanide detoxification sulfurtransferase, whereas genes encoding the co-chaperone GroES, the LysE superfamily of lysine exporters, short-chain alcohol dehydrogenase and the potential c-di-GMP phosphotransferase were downregulated. Our results suggest that epinephrine may stimulate matrix synthesis in M. luteus biofilms, thereby increasing the activity of NAD(H) oxidoreductases. Potential c-di-GMP pathway proteins are essential in these processes.

Controlling the formation and reconstruction of microbial biofilms is of ever increasing importance for the ecological, medical, and biotechnological aspects of biofilm studies. The goal of this review was to provide systematization and analysis of the results obtained in recent years on the modes and mechanisms of the stimulatory or inhibitory effect of extreme factors and biocidal agents on biofilm formation. Special attention is paid to controlling the formation of medically (infective diseases, implant biofouling) and technologically or biotechnologically important biofilms (bioremediation, biocorrosion, and biosynthesis of biologically active compounds).

Search for inexpensive efficient compounds with antibiofilm activity, which could be applied both for treatment of biofilm-associated infections and in other cases requiring biofilm elimination, is presently of importance. For this purpose we chose niclosamide. Niclosamide is a widespread and available anthelmintic drug, which was also recently shown to suppress bacterial growth. High antibiofilm activity of niclosamide against a range of gram-positive bacteria isolated from different ecological niches was shown. According to our results, niclosamide may be a promising component of composite antibiofilm preparations.

Kytococcus schroeteri strain H01 was isolated from the skin of a healthy volunteer who underwent erythromycin treatment for a skin disorder 1 year prior. The draft genome consists of 2.38 Mb, a G+C content of 73.06%, and 2,221 protein coding sequences. This is the first genome characterization of a K. schroeteri strain isolated from human skin.

The effect of norepinephrine (“NE”) on Gram-negative bacteria is well characterized; however, little is known about the impact of NE on cutaneous Gram-positive skin residents, especially staphylococci. In this study, the impact of NE on monospecies and dual-species biofilms of Staphylococcus epidermidis and S. aureus model strains was investigated for the first time. Biofilms were grown in two different models (on polytetrafluoroethylene (“PTFE”) cubes and glass microfiber filters (“GMFFs”)) and additionally kinetic measurements of bacterial growth was performed. We have shown that NE can affect the biofilm formation of both species with a strong dependence on aerobic or anaerobic culture conditions in different models. It was shown that S. epidermidis suppresses S. aureus growth in dual-species biofilms and that NE can accelerate this process, contributing to the competitive behavior of staphylococci.

Staphylococcus aureus and Cutibacterium acnes are common representatives of the human skin microbiome. However, when these bacteria are organized in biofilm, they could be involved in several skin disorders such as acne or psoriasis. They inhabit in hollows of hair follicles and skin glands, where they form biofilms. There, they are continuously exposed to human hormones, including human natriuretic peptides (NUPs). We first observed that the atrial natriuretic peptide (ANP) and the C-type natriuretic peptide (CNP) have a strong effect S. aureus and C. acnes biofilm formation on the skin. These effects are significantly dependent on the aero-anaerobic conditions and temperature. We also show that both ANP and CNP increased competitive advantages of C. acnes toward S. aureus in mixed biofilm. Because of their temperature-dependent effects, NUPs appear to act as a thermostat, allowing the skin to modulate bacterial development in normal and inflammatory conditions. This is an important step toward understanding how human neuroendocrine systems can regulate the cutaneous microbial community and should be important for applications in fundamental sciences, medicine, dermatology, and cosmetology.

Increasing popularity of preservative‐free cosmetics necessitates in‐depth research, specifically as bacteria can react to local factors by important metabolic changes. In this respect, investigating the effect of cosmetic preparations on pathogenic strains of commensal species such as acneic forms of Cutibacterium acnes (former Propionibacterium acnes) and bacteria behaving both as commensals and opportunistic pathogens such as Staphylococcus aureus is of major interest. In this study, we studied the effect of commonly used cosmetics, Uriage™ thermal water (UTW) and a rhamnose‐rich polysaccharide (PS291®) on RT4 and RT5 acneic strains of C. acnes and a cutaneous strain of S. aureus. UTW affected the growth kinetic of acneic C. acnes essentially by increasing its generation time and reducing its biomass, whereas only the S. aureus final biomass was decreased. PS291 had more marginal effects. Both compounds showed a marked antibiofilm activity on C. acnes and S. aureus. For S. aureus that appeared essentially due to inhibition of initial adhesion. Cosmetics did not modify the metabolic activity of bacteria. Both C. acnes and S. aureus showed marked hydrophobic surface properties. UTW and PS291 had limited effect on C. acnes but increased the hydrophobic character of S. aureus. This work underlines the effect of cosmetics on cutaneous bacteria and the potential limitations of preservative‐free products.

The structure, composition, and developmental patterns of multi-species biofilms are analyzed, as are the mechanisms of interaction of their microbial components. The main methodological approaches used for analysis of multi-species biofilms, including omics technologies, are characterized. Environmental communities (cyanobacterial mats and methanotrophic communities), as well as typical multi-species communities of medical importance (oral cavity, skin, and intestinal microbiomes), are described. A special section deals with the role of multi-species biofilms in such biotechnological processes as wastewater treatment, heavy metal removal, corrosion control, and environmental bioremediation.

Bacterial biofilms constitute a critical problem in hospitals, especially in resuscitation units or for immunocompromised patients, since bacteria embedded in their own matrix are not only protected against antibiotics but also develop resistant variant strains. In the last decade, an original approach to prevent biofilm formation has consisted of studying the antibacterial potential of host communication molecules. Thus, some of these compounds have been identified for their ability to modify the biofilm formation of both Gram-negative and Gram-positive bacteria. In addition to their effect on biofilm production, a detailed study of the mechanism of action of these human hormones on bacterial physiology has allowed the identification of new bacterial pathways involved in biofilm formation. In this review, we focus on the impact of neuropeptidic hormones on bacteria, address some future therapeutic issues, and provide a new view of inter-kingdom communication.

O-Specific polysaccharides were obtained from the lipopolysaccharides isolated from the planktonic and biofilm cultures of Pseudomonas chlororaphis 449 and studied by composition analysis and 1D and 2D (1)H and (13)C NMR spectroscopy. The following structure was established: --4)-α-D-GalpNAc6Ac-(1--3)-β-D-QuipNAc-(1--6)-α-D-GlcpNAc-(1--β-D-GlcpNAc-(1--3) where the degree of non-stoichiometric 6-O-acetylation of GalNAc is ∼ 60% in the planktonic form or ∼ 10% in biofilm.

Growth of members of most of the studied genera of gram-positive (Dietzia, Kocuria, and Rhodococcus) and gram-negative bacteria (Pseudomonas and Chromobacterium) in biofilms exhibited higher resistance to a translation inhibitor, azithromycin compared to the growth of planktonic cultures of the same strains. Low concentrations of azithromycin were found to stimulate biofilm formation by the studied saprotrophic strains. The rate of synthesis of the polysaccharide matrix component exceeded the rate of cell growth, indicating implementation of the biofilm phenotype under these conditions. It was found that an alkylhydroxybenzene (AHB) compound 4-hexylresorcinol was capable of almost uniform suppression of growth of both planktonic cultures and biofilms of the saprotrophic strains under study. In some cases, combined action of azithromycin and AHB resulted in an additive inhibitory effect and prevented the stimulation of biofilm growth by subinhibitory azithromycin concentrations. Thus, AHB may be considered a promising antibiofilm agent.

The data on the composition and structure of the components comprising the extracellular polymer matrix of bacterial biofilms, the role of these components, and their functions in the biofilm are reviewed. The main biochemical mechanisms regulating the biosynthesis of biofilm matrix are discussed.

International audience; Neurohormones diffuse in sweat and epidermis leading skin bacterial microflora to be largely exposed to these host factors. Bacteria can sense a multitude of neurohormones, but their role in skin homeostasis was only investigated recently. The first study focused on substance P (SP), a neuropeptide produced in abundance by skin nerve terminals. SP is without effect on the growth of Gram-positive (Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis) and Gram-negative (Pseudomonas fluorescens) bacteria. However, SP is stimulating the virulence of Bacillus and Staphylococci. The action of SP is highly specific with a threshold below the nanomolar level. Mechanisms involved in the response to SP are different between bacteria although they are all leading to increased adhesion and/or virulence. The moonlighting protein EfTu was identified as the SP-binding site in B. cereus and Staphylococci. In skin nerve terminals, SP is co-secreted with the calcitonin gene-related peptide (CGRP), which was shown to modulate the virulence of S. epidermidis. This effect is antagonized by SP. Identification of the CGRP sensor, DnaK, allowed understanding this phenomenon as EfTu and DnaK are apparently exported from the bacterium through a common system before acting as SP and CGRP sensors. Many other neuropeptides are expressed in skin, and their potential effects on skin bacteria remain to be investigated. Integration of these host signals by the cutaneous microbiota now appears as a key parameter in skin homeostasis.

Biofilms of a number of gram-positive and gram-negative bacteria (both environmental strains from the stratal waters of oil fields and collection strains) were found to exhibit higher resistance to extreme physicochemical factors (unfavorable temperature, pH, and salt concentration) than planktonic cultures. The extracellular polymers forming the structure of the biofilm matrix were shown to contribute significantly to this resistance, since suppression of matrix formation by subbacteriostatic concentrations of azithromycin (for Pseudomonas acephalitica) or mutation in the cvil gene encoding N-hexanoyl homoserine lactone synthetase (for Chromobacterium violaceum CV026) resulted in the resistance of biofilms being decreased almost to the level of planktonic cultures. The role of the biofilm matrix for bacterial survival under extreme conditions is discussed.

Установлено, что биопленки ряда грамположительных и грамотрицательных бактерий (как изолированных из пластовых вод нефтяного месторождения, так и коллекционных штаммов) обладают повышенной по сравнению с планктонными культурами устойчивостью к экстремальным физико-химическим условиям среды (неблагоприятной температуре, рН и концентрации соли). Показано, что существенную роль в этой устойчивости играют внеклеточные полимерные вещества, составляющие структуру матрикса биопленки, поскольку при подавлении образования матрикса под воздействием суббактериостатических концентраций антибиотика азитромицина (в случае Pseudomonas acephalitica), а также в результате мутации гена cvil, кодирующего синтетазу N-гексаноилгомосеринлактона (в случае Chromobacterium violaceum CV026), чувствительность биопленок к экстремальным факторам среды снижается практически до уровня планктонных культур. Обсуждается значение матрикса биопленки для выживания бактерий в экстремальных условиях.

The review considers the main mechanisms of metabolism regulation that operate in pro- and eukaryotic microorganisms upon changes in the partial pressure of oxygen in the medium, i.e., upon transition from normoxia via hypoxia to anoxia or upon the reverse transition. The involvement in these processes of hemes, the Hap transcription factors, the Rox1 repressor protein, sterols, and other regulatory factors is discussed.

A number of halotolerant and halophilic bacterial strains were isolated from the Romashkinskoe oil field (Tatarstan) stratal waters having a salinity of up to 100 g/l. The isolation of pure cultures involved biofilm reconstitution on M9 medium with paraffins. The associations obtained were dispersed and reinoculated onto solid media that contained either peptone and yeast extract (PY medium) or paraffins. It was shown that such associations included both oil-oxidizing bacteria and accompanying chemoheterotrophic bacteria incapable of oil oxidation. The pure cultures that were isolated were used for creating binary biofilms. In these biofilms, interactions between halophilic and nonhalophilic bacteria under hypo-and hyperosmotic shocks were investigated. We conducted a detailed study of a biofilm obtained from an oil-oxidizing halotolerant species (with an upper growth limit of 10–12% NaCl) identified as Dietzia sp. and an extremely halophilic gram-negative bacterium (growing within the 5–20% NaCl concentration range) of the genus Chromohalobacter that did not oxidize paraffins. If these microorganisms were grown in a mixed suspension (planktonic) culture that was not supplemented with an additional amount of NaCl, no viable cells of the halophilic microorganism were detected after reinoculation. In contrast, only halophilic cells were detected at a NaCl concentration of 15%. Thus, no mutual protective influence of the microorganisms manifested itself in suspension culture, either under hypoor under hyperosmotic shock. Neither could halophile cells be detected after reinoculating a biofilm obtained on a peptone medium without the addition of NaCl. However, biofilms produced at a NaCl concentration of 15% contained approximately equal numbers of cells of the halophilic and halotolerant organisms. Thus, the halophile in biofilms sustaining a hyperosmotic shock exerts a protective influence on the halotolerant microorganism. Preliminary data suggest that this effect is due to release by the halophile of osmoprotective substances (ectoine and glutamate), which are taken up by the halotolerant species. Such substances are diluted by a large medium volume in suspension cultures, whereas, in biofilms, their diffusion into the medium is apparently hampered by their interaction with the intercellular polymer matrix.

The definition of the term "biofilm" and the validity of the analogy between these structured microbial communities and multicellular organisms are discussed in the review. The mechanisms of biofilm formation, the types of interrelations of the components of biofilms, and the reasons for biofilm resistance to biocides and stress factors are considered in detail. The role of biofilms in microbial ecology and in biotechnology is discussed.

It was shown that two stress factors, hypoxia and hyperosmotic shock, if applied simultaneously to the yeast Debaryomyces hansenii, display an antagonistic mode of interaction, which results in an increased degree of halophily of this microorganism under microaerobic conditions. Studies of the effects of respiration inhibitors (sodium azide and salicyl hydroxamic acid, SHA) and of the pattern of changes in the composition of the respiratory chain of Debaryomyces hansenii under the stated stress conditions led to the suggestion of three (or four) chains of electron transfer functioning simultaneously in the cell: the classical respiratory chain involving cytochrome-c oxidase, an alternative respiratory chain involving a cyanide- and azide-resistant oxidase, and additional respiratory chains involving oxidases resistant to salt, azide and SHA. Thus, the antagonistic mode of interaction between hypoxia and hyperosmotic shock results from the redirection of the electron flow from the salt-susceptible respiratory systems to the salt-unsusceptible ones encoded by "the hypoxia genes" and activated (induced) under microaerobic conditions.

Peculiarities of the structural organization in non-spore-forming bacteria associated with long-term anabiosis were revealed both in laboratory cultures and in natural populations isolated from 1–3-Myr-old Eastern Siberian permafrost and tundra soil. Different advanced methods were used, including (a) high-resolution electron microscopy; (b) simulation of in situ conditions in the laboratory by varying the composition of growth medium and cultivation conditions; (c) low-temperature fractionation to isolate and concentrate microbial cells from natural soils; (d) comparative morphological analysis of microbial cells in model cultures and natural soils (in situ). Under laboratory conditions, the intense formation of resting cells by representatives of various taxa of eubacteria and halophilic archaea occurred in 2–9-month-old cultures grown in carbon-, nitrogen-, or phosphorus-limited media, in starved cell suspensions in the presence of sodium silicate, or on soil agar. Among resting cells, we revealed cystlike forms having a complicated structure and common features. These included a thick capsule; a thickened and multiprofile cell wall; the presence of large intramembrane particles on PF- and EF-fracture surfaces; fine-grained or lumpy cytoplasm; and a condensed nucleoid. The general morphological properties, ultrastructural organization, physiological features of cystlike cells, and their ability to germinate under the appropriate conditions suggest the existence of constitutive dormancy in non-spore-forming bacteria. It was found that the majority of microorganisms in permafrost and tundra soil are cystlike cells, very similar to those in laboratory cultures. Anabiotic (resting) cystlike cells are responsible for the survival of non-spore-formers in extreme Earth habitats and may be regarded as possible analogs of extraterrestrial forms of microbial life.

The biochemical mechanisms were studied that determine different reactions of yeasts of different genera to two simultaneously imposed stressors, hypoxia and osmotic shock. For Candida lipolytica, these two stressors were antagonistic, which resulted in stimulation (and not suppression) of the growth of this yeast by NaCl (in a wide range of concentrations) under microaerobic conditions. The reaction of Malasseziasp. was different: the degree of halotolerance of this microorganism was lower under microaerobic conditions. An intervening reaction pattern was characteristic of Rhodotorula aurantiaca.These differences were found to be determined, above all, by the induction of a salt-resistant respiratory system (oxidase) in C. lipolytica, which could not be induced in Malassezia sp. In addition, the synthesis of catalase was enhanced in C. lipolytica, which provided for neutralization of the active forms of oxygen accumulating as a result of inhibition of other protective enzymes by salt.

Two stress factors, hypoxia (microaerobic conditions) and a high salt concentration, if applied simultaneously to aerobic microorganisms, display an antagonistic mode of interaction. As a result, the NaCl level that is usually optimal for moderate halophiles (5-6%) becomes optimal for the growth of weak halophiles (Rhodococcus erythropolis and Shewanella sp. CN32); the halotolerant yeast Yarrowia lypolytica acquires halophilic properties (with a growth optimum at a NaCl concentration of 10%), and the growth rate of the extremely halophilic Halobacterium salinarum increases at supraoptimal salt concentrations (25-34%). This phenomenon is apparently due to multiple changes in metabolic reactions. In particular, high salt concentrations suppress respiration and the formation of enzymes (superoxide dismutase and catalase) that protect the cell from toxic oxygen species. Therefore, establishment of microaerobic conditions compensates for the loss of these protective mechanisms and enables cell growth at higher salt concentrations than under aerobic conditions. Of some importance can also be the increase in the intracellular concentrations of osmoprotectants caused by the suppression of their intracellular oxidation. The implications of this phenomenon for the ecophysiology of microorganisms (including oiloxidizing species) and for the classification of weak and moderate halophiles are discussed.

The degree of halophily inRhodococcus erythropolis andHalobacterium salinarum was found to increase under microaerobic conditions. This was evidently due to the fact that the two stress factors (high salt and low oxygen concentrations) acted in an antagonistic manner. The results obtained suggest that the aeration rate should be taken into account while estimating the degree of halophily of a microorganism.

The growth characteristics of an algo-bacterial community (Chlamydomonas reinhardtii and bacterial satellites) were studied, as well as the mechanism and patterns of bacterial effect on algae. Four strains of predominant bacteria were isolated and partially characterized. They were assigned to the following taxa: Rhodococcus terrea, Micrococcus roseus, and Bacillus spp. A pure culture of the alga under study was obtained by plating serial dilutions on agarized media. Within the algo-bacterial association, the alga had a higher growth rate (0.76 day−1) and yield (60 μg chlorophyll/ml culture) than in pure cultures (0.4 day−1 and 10 μg chlorophyll/ml culture, respectively). The viability of the algal cells within the association was retained longer than in pure culture. Among the isolated bacterial satellites, strains B1 and Y1, assigned to the species Rhodococcus terrae, had the highest stimulatory effect on algal growth. The culture liquid of bacteria incubated under the conditions not permitting growth stimulated algal growth; the culture liquid of actively growing bacteria had an opposite effect.