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Streptomycetes, soil-dwelling mycelial bacteria, can form biofilms as indigenous components of the environment. The biofilms formed by streptomycetes exist in different ecological niches, in natural, medical, industrial environments. The biofilm-forming streptomycetes affect water quality, human health, associate with deterioration of artworks and historical monuments. The review should be of interest for researchers of the biofilm mode of streptomycetes growth.

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Streptomycetes or mycelial microorganisms are able to form biofilms under the natural, industrial and clinical conditions. The controlled use of biofilms in various industrial processes is much more efficient vs. the cultivation of plankton suspended cells. Optimization of biotechnological processes with the use of streptomycete biofilms is advisable in production of lactic acid and detoxication of the liquor in pyrolysis of plant biomass. Streptomycete biofilms are used in water purification systems. It is recommended to use biofilms for detoxication of wastes and bioremediation of soils contaminated with hard metals. The use of biofilms of streptomycetes producing biologically active substances is of special interest. High yields of.antibiotics and actinomycin D in particular was observed with. cultivation of antibioc-producing streptomycetes as biofilms in bioreactors of unique design.

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It was thought that antibiotics should be produced by soil microorganisms to inhibit the growth of competitors in natural habitats. Yet it has been shown that antibiotics at subinhibitory concentrations may have a role as signalling molecules providing cell-to-cell communication in bacteria in the environment. Antibiotics modulate gene transcription and regulate gene expression in microbial populations. Subinhibitory concentrations of antibiotics may cause a number of phenotypic and genotypic changes in microorganisms. These transcription changes are dependent on the interaction of antibiotics with macromolecular receptors such as ribosome or RNA-polymerase. Antibiotic signalling and quorum-sensing system are important regulatory mechanisms in bacteria. It was demonstrated that antibiotics interfered with quorum-sensing system.

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It is shown that the actinomycete complex in steppe-desert light brown salty soil of desert steppes of Mongolia is represented by the genera Streptomyces and Micromonospora. The species diversity of the genus Streptomyces, which dominates the complex, decreases with increasing osmolarity of the medium. The influence of environmental factors--temperature and osmolarity of medium--on the development of metabolically active members of the phylum Actinobacteria in the domain Bacteria of the prokaryotic microbial soil community was established. The proportion of metabolically active bacteria belonging to Actinobacteria increases with increasing osmolarity and incubation temperature of soil. The dominance of the filamentous metabolically active members of the phylum Actinobacteria over the unicellular organisms was shown. The halotolerant actinomycetes isolated from the steppe-desert soils were alkalotolerant, xerophilic, and thermotolerant and exhibited antimicrobial activity with respect to Gram-positive bacteria and actinomycetes.

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The known conceptions of resistome as a complex of all the antibiotic resistance genes in the genomes of all the microorganisms, pathogenic and nonpathogenic ones, in nature are considered. The data on the origin, evolution and distribution of antibiotic resistance genes and possible approaches to the resistance distribution control are presented.

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It has been demonstrated that complexes of mycelial bacteria (actinomycetes), in which the amount of psychrotolerant actinomycetes reaches hundreds of thousands of CFU/g of the soil (frequently exceeding the portion of mesophilic forms), are developed in peat and podzolic soils of the tundra and taiga at low temperatures. As actinomycetes grow and develop in cold soils, their mycelium increases in length. Use of the molecular in situ hybridization method (fluorescent in situ hybridization, FISH) demonstrated that the portion of metabolically active mycelial actinobacteria exceeds the portion of unicellular actinobacteria in the Actinobacteria phylum. Specific peculiarities of psychrotolerant populations in relation to the spectrum of consumed substrates (histidine, mannitol, saccharose) were established by the method of multirespirometric testing.

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Physiological aspects of Streptococcus lactis, strain MSU development in mixed culture with Rhodotorula colostri were studied in connection with nisin biosynthesis. By the IR spectra the average content of the main components in the monoculture cells of S. lactis and its association with the yeast in the stationary growth phase was the following by dry weight: 54-58 per cent of protein, 14-16 per cent of nucleic acids, 26-28 per cent of carbohydrates and 3-5 per cent of lipids. Glucose and nitrogen in the fermentation broth were consumed completely. A significant quantity of KH2PO4 remained in the fermentation broth. Lactic acid excretion was observed. S. lactis, strain MSU was the leading component of the association under the studied cultivation conditions because just its IR spectra dominated in the spectra of the mixed culture.

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A procedure for protoplasts of Str. lactis producing nisin was developed. The following lysing factors were used for obtaining the protoplasts: lycozyme, LE enzyme, lysosubtilin and an enzyme isolated from the culture fluid A. levoris. The use of the above factors in different combinations provided an increase in the number of the formed protoplasts from 1-2 in the field of the microscope vision to 15-20, which amounted to 25 per cent of the total number of the cells visible under microscope.

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The interaction between populations was studied with Arthrobacter crystallopoietes and Streptomyces olivocinereus, an actinomycete producing the antibiotic heliomycin active against Gram-positive microorganisms. The two organisms were either cultivated together in a growth medium or the two populations were introduced simultaneously into nonsterile soil at different levels of population density. The antagonism was found in both cases: A. crystallopoietes cells died off when a population of the potential antagonist was added. The density of a population producing the antibiotic had to be sufficiently high for the antagonism to be manifested. The antagonism influenced the dynamics of a population of the antibiotic-sensitive microorganism. The results have confirmed earlier data to the effect that antibiotic synthesis is possible in nonsterile soil.

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The dynamics of Rhizobium leguminosarum and Arthrobacter crystallopoietes populations introduced into soil at different levels of density was studied in a zone near barley roots. Microbial life with a high rate of growth was found only at the root surface. For A. crystallopoietes, the ultimate bacterial incidence at the root surface was found to depend on the original level of population density. For Rh. leguminosarum, the ultimate incidence was shown to reach an identical level irrespective of the original population density. Apparently, the identical level of stabilization in Rh. leguminosarum and the dependence of the ultimate incidence of A. crystallopoietes on the original population density reflect the peculiarities of ecological strategies displayed by these microorganisms. The introduction of A. crystallopoietes and Rh. leguminosarum into soil had no effect on the dynamics of soil bacteria assayed by the inoculation method.

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The survival of a population of nodule bacteria after its introduction into soil depends on the ratio between favourable and unfavourable microzones. This ratio does not remain constant in one and the same soil at different stages of microbial succession even if the succession is caused by simple humidification of the soil without any introduction of additional substrates. The dynamics of the incidence of nodule bacteria introduced, at one and the same level, into soil samples of different growth stages of a complex of soil microorganisms significantly differed. Successful nitragination may be assisted by determining the growth stage of a microbial system when the population is being introduced and by changing the environment in the soil.

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The dynamics of bacterial and fungal incidence in two sharply different soil samples after the addition of water and glucose was studied using direct microscopic techniques and a technique of inoculation in growth media. The ratio of the population density indices established by means of microscopy to those found from the data of inoculation characterizes the stage of microbial succession. The techniques of microscopy and inoculation are equitable, furnish different information, and must be used in parallel while examining various problems pertinent to the dynamics of the soil microflora incidence.

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The dynamics of individual components from the complex of soil microorganisms (bacteria, fungi, actinomycetes) and the population of Stm. olivocinereus introduced into soil was studied by luminescent microscopy and inoculation. The population density maxima for individual components from the complex of soil microorganisms were shown to be separated in time suggesting a succession. Fungi developed at the first steps of succession and dominated in biomass over the remaining components of the complex. Bacteria and actinomycetes developed at the later steps of succession. Glucose addition stimulated still earlier growth of fungi (the maximal mycelium legth was registered by the second day) but had hardly any effect on the dynamics of other components of the complex.

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Soil microorganisms can be quantitatively assayed by means of a technique which makes use of staining preparations on slides with acridine orange. When bacterial cells were counted daily in humus-gleisolic soil, their number did not depend on time if the soil was incubated for five days. Mixed soil samples corresponding to the same time of incubation differed reliably in the bacterial number. The paper presents a scheme for determining the necessary number of samples, preparations, and fields of vision when the number of bacteria is being estimated. It is expedient to take 7 samples from a soil mixture, to make 2 preparations out of each sample, and to count bacteria in 5 fields of vision for each preparation.

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The dynamics of the population of the soil actinomycetes Streptomyces olivocinereus can be studied in its natural habitat using a conventional technique of inoculation at a level of the population density close to the natural one. The colonies are registered and counted in UV where they are clearly visible due to their bright orange luminescence. Techniques employed for obtaining information about the population structure (spores--mycellium) are described. The dynamics of the population has been studied within a year. The population introduced into soil is stabilized at a relatively high level.

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Indices of the radial growth rate of colonies were determined for Circinella circinans and Mortierella ramanniana as well as for the complex of fungi in soil in the course of microbial succession. The maximum of growth (Kr = 0.053 cm/hr) for C. circinans was observed at a high concentration of glucose (10%) in the medium, whereas for M. ramanniana the maximum (Kr = 0.0054 cm/hr) was detected at a low glucose concentration (0.005%) in the medium. These data account for the position of C. circinans and M. ramanniana in the course of microbial succession in the natural habitat. Kr was used to establish the origin of successional changes in the complex of soil fungi in serozem upon the introduction of glucose.

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Relation between the growth of the heliomycin-producing organisms, biosynthesis of the antibiotic and morphological differentiation of the mycelium was studied. The curves of the culture growth were of diauxic nature. The synthesis of heliomycin was parallel to the organism active growth (trophophase). The antibiotic was synthesized in the germinating spores and localized in the areas of active growth and surface structures. The indicator properties of heliomycin were also evident in the organism mycelium. The antibiotic was registered in the young hyphae mainly in an oxidated form timed to the membrane structures. With the culture development heliomycin accumulated in the mycelium in reduced form together with lipids in the form of granules (vacuole structures). Condensation of heliomycin in the vacuoles (granules) started during the 2nd lag-phase, and may be associated with both heliomycin storing and inclusion of detoxication mechanisms. It was shown that heliomycin was consumed in the culture under conditions of starvation. In this case the antibiotic granules disappeared. The connection between the synthesis of heliomycin and the organism active growth, localization of the antibiotic in the areas of active growth, consumption of the antibiotic under conditions of starvation indicate that heliomycin is important for the organism and participates in the processes of growth and metabolism.

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Ultrasonic treatment of soil, though being very effective for desorption of cells and deaggregation of microcolonies, may damage and kill microorganisms. Possible application and effectiveness of ultrasonic treatment was studied in this work with chernozem (dry and wet samples), rhizosphere and rhizoplane of pea. An ultrasonic disintegrator of low frequency is recommended for dry soils. Ultrasound cannot be recommended for treating rhizosphere and rhizoplane of plants without checking its effectiveness in each case.

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