The article deals with the formation and development of the physiological methodological approach to microbial life-sustaining activities as related to M.V. Gusev’s scientific achievements. It summarizes Gusev’s concepts on microbial physiology and its role in the system of the life sciences. The main research directions developed at the Department of Microbial Physiology at M.V. Lomonosov Moscow State University are outlined.

Complex ecosystem of humans and microbes has been presented as a associative symbiosis, based on a mutual support of symbionts with different consequences for them. Conditions for the persistence of bacteria have been defined: their resistance to the outdoor environment factors, antagonism in biocenosis and stability to host defence mechanisms.
The key role of bacterial peptidoglycane has been defined for their survival in infected organism, and the classification for persistent mechanisms of pathogens has been given. The group of bacterial secreted protease, providing microbial resistance to defence factors of an organism, has been described.
Host colonizing resistance has been presented as a physiological regulatory system, controlling bacterial penetration into an organism. Regulatory mechanisms for bacterial persistence have been discussed.

The whole-genomic analysis in silico of 64 free-living prokaryotic species has been performed to determine the number, length, distribution and location of direct and inverted intragenomic repeated sequences (LRS). Three main types of lengthy ( 500 bp) repeated sequences were revealed: a) associated with ribosomal RNA genes; b) with copies of protein coding genes; c) with IS-elements and genes encoding putative transposases. Lengthy repeated sequences related to transposases comprise 50—95% of total number of LRS depending on species. Intragenomic LRS associated with transposases and IS-elements can reflect a recombinational potential of different prokaryotic species determining both the ability to adaptive gene rearrangements and cell capacity for integration of genes acquired through horizontal transfer ways.

Cyanobacterial biodiversity is paradoxical, since they strongly vary in cytological characters being metabolically uniform. Cyanobacterial phylogeny is also paradoxical, since structural genes of rRNA are too conservative for a large phylum. On the paradoxical evolutionary tree, neighbors with strongly contrast phenotypes reside, while objects with alike phenotypes demonstrate heterological structure of 16S rDNA. Cyanobacterial systematics is paradoxical too, since it is logically contradictory (on the one hand, phylum BX Cyanobacteria generally separates itself on molecular-biological grounds; on the other hand, in accordance with traditional botany algorithm which is used in the classification of blue-green algae, this phylum artificially subdivides itself in morphological groups (ultrastructural characters are taken into account in rare instances only). The unique peculiarity of cyanobacterial taxonomy (with rare exceptions, e.g. Cyanobacterium stanieri) is its general non-usage of the category of species; species epithet is substituted for by strain index (e.g. Anabaena sp. PCC 7122).

Bacteria are capable “to sense” an increase of cell density population and to reply on it by the induction of special sets of genes. This type of the regulation named quorum sensing (QS) includes the production and excretion from cells into the medium low-molecular-weight signaling molecules (autoinducers, AI) which readily diffuse through a cell wall. As the bacterial population reaches a critical level of density, the concentration of these signaling molecules in medium increases as a function of density population. On reaching a critical threshold concentration, AIs bind to the specific receptor regulatory proteins which induce the expression of target genes. By means of AIs bacteria accomplish communication that is transmission of the information between bacteria belonging to the same or different species, genera, and even families — signaling molecules of some bacteria act on the receptors of others, resulting in coordinated reply of bacterial cells in population. Bacteria of different taxonomic groups use QS systems in the regulation of the broad range of physiological activities. These processes involve virulence, symbiosis, conjugation, biofilms formation, bioluminescence, synthesis of enzymes, antibiotic substances etc. Here we review the different QS systems of bacteria, the role of QS in bacteria communication and some applied aspects of QS regulation application.

The article presents the historical analysis of the development of population approach in cytology of microorganisms. Special attention is paid to the structural fundamentals of the organization of developing bacterial population as a holistic self-regulated system featuring cell specialization and cooperation. The structural and functional properties, the proportion of different cell types formed during population development under certain environmental conditions as well as the structural fundamentals of cell interaction are proposed as the subject of procaryote population cytology. The interrelationship of the phenotypical and ultrastructural plasticity concepts in bacteria is discussed. The results of the experiments carried out by the author on cyanobacteria in natural and model plant symbioses are employed as an evidence of efficiency of the ultrastructural plasticity-based criteria use as the markers of operation of adaptation mechanisms implemented on subcellular, cellular and population levels.

Physiology is a science on functions. Functions of microorganisms, as for every living thing, are metabolism and energy provision, reproduction and death, regulation of vital activity on the intracellular level and on the level of interactions between microbial cells and abiogenous factors, on the level of microbe-microbial interactions and interactions of microorganisms with plants, animals and man. According to metabolic and energetic potentials, microorganisms are subdivided into photo- and chemotrophs, litho- and organotrophs, auto- and heterotrophs; procaryotic organisms assimilate molecular nitrogen. The noted functions are subjected to versatile regulation that is a basis for intra- and intercellular communications. Microbial responses to exposure on macroorganisms is an introduction or a prevention of programmed cell death (PCD) in infected organisms, a change to inactive state (persistence). An induction of programmed cell death in cells affected by illness that can be spreaded to sound cell and organisms, an induction of PCD in pathogens penetrating in macroorganism, a change of persister cell of pathogens into active state, suppression of density effects in microbial populations (quorum sensing) are important trends in microbial physiology and biotechnology of medical and prophylactic preparations.

Parietochloris incisa is a unicellular, fresh water green alga, capable of accumulating high amounts of the valuable very long chain polyunsaturated arachidonic acid (AA) in triacylglycerols (TAG) of cytoplasmic oil-bodies. To find out the cultivation conditions providing maximum AA yield, the effects of light irradiance and N- availability on the dry weight (DW), chlorophyll, carotenoid and AA content have been studied. Under nitrogen starvation, TAG accounted for over 30% of dry weight (DW) and AA content became as high as ~ 55% of total fatty acids. From the standpoint of biomass accumulation, light intensity of ca. 400 uE m–2 · s–1 was found to be optimal for growing P. incisa on complete medium. Lower light intensities (or higher cell density of inoculum) resulted in higher AA yield when the alga was cultivated on nitrogen-free media. In the absence of nitrogen, algal cells were unable to cope with high light and suffered from photooxidative damage, whereas the nitrogen-sufficient culture survived under such illumination conditions probably due to accumulation of carotenoids. Nitrogen-deprived P. incisa cells displayed elevated sensitivity to light.