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Plants’ adaptations, in combination with the rhizosphere and endosphere microbiome, ensure their survival in the extreme conditions of the Antarctic. The work aimed to quantify the culturable microorganisms of different groups and establish the plant growth-promoting potential of bacterial isolates from the rhizosphere of Deschampsia antarctica. Standard microbiological methods (enumeration of microorganisms and study of the properties of isolates, in particular, the cell wall organization by Gram staining, motility, endospore formation, growth at different temperatures, halotolerance, need for oxygen, ability to assimilate some organic carbon sources) and biochemical methods to determine the properties of isolates (oxidase, catalase activities, tests for the ability to reduce nitrate, produce amylases, lipases, proteases). The ability of the isolates to produce siderophores was determined using a medium with chromazurol S and hexadecyltrimethylammonium bromide, to solubilize insoluble phosphate-containing compounds using Pikowska’s medium with Ca3(PO4)2 and Menkina’s medium with egg lecithin. The content of auxin-like substances in the medium was determined by the Salkowski method. The effect of the isolates on wheat growth was determined by the germination of wheat seeds treated with the isolates, the length of shoots and roots of plants, and chlorophyll content in leaves. The isolates were identified using phylogenetic analysis of the 16S rRNA gene. The most abundant groups of microorganisms in the rhizosphere of D. antarctica were oligotrophic, oligonitrophilic, and cellulose-degrading microorganisms. Among 120 isolates of the rhizosphere zone of D. antarctica, 7 oligonitrophilic isolates (RE1, RE3, RE4, RE8, RP8, RO4, RT1) were selected, which solubilized insoluble phosphatecontaining compounds, synthesized lipases, amylases, auxin-like substances, and siderophores. Isolate RT1 (Bacillus sp. RT1 by physiological and biochemical properties and the 16S rRNA gene) showed the best plant growth-promoting properties. Treatment of wheat seeds with this isolate increased germination by 25%, shoot and root length by 15%, leaf area 3 times, and chlorophyll content 1.6 times.

Microorganisms are exposed to reactive oxygen species (ROS) that are formed in various ways, in particular, as a result of respiration or other intracellular processes, during metal-catalyzed Fenton reactions, as a result of the action of UV- and X-radiation, under the influence of some antimicrobial drugs, or during the host immune oxidative-burst response against infection agents. In this review, we take a look at the mechanisms of microbial cell damage, including damage of lipids and proteins. Lipid peroxidation (LPO) is one of the main molecular mechanisms involved in oxidative damage to cellular structures. A variety of products are formed during LPO reactions: alkoxyl radicals, peroxyl radicals, hydroperoxides, diene conjugates, carbonyl compounds, aldehyde adducts with biopolymers, alcohols, esters, etc. These products include cytotoxic and highly reactive compounds. Free radical reactions of protein damage occur via hydrogen atom abstraction from α-carbon or SH-, NH2-groups of aminoacids and electron abstraction from nucleophile centers of proteins resulting in the fragmentation of proteins, their denaturation and the formation of amino acid radicals. Bacteria show a significant adaptive potential to the influence of stress agents, including ROS. We summarized the data on bacterial antioxidant protection, ROS redox sensors, and regulators of bacterial cell response to ROS exposure, focusing on the features of anaerobic microorganisms, as their responses to the oxidative damage are the least studied, and many problems remain unsolved. This review contains information about changes in fatty acid composition of lipids of the plasma membrane to maintain the necessary fluidity, and, thus, counteract the effects of various stressing agents, including ROS. The main modifications of the fatty acid composition of lipids important for the regulation of membrane fluidity are described, in particular, via changes in the degree of lipid saturation, cis/trans isomerization, and synthesis of cyclopropane fatty acids.