Detergent-Resistant Membranes in Chloroplasts and Mitochondria of the Halophyte Salicornia perennans under Salt Stress

Halophytes represent important models for studying the key mechanisms of salt tolerance. One approach to the development of new knowledge of salt tolerance is to study the properties of detergent-resistant membranes (DRMs). In this work, the lipid profiles of DRMs of chloroplasts and mitochondria of euhalophyte Salicornia perennans Willd, before and after their exposure to shock concentrations of NaCl, have been investigated. We found that DRMs of chloroplasts are enriched in cerebrosides (CERs) and that sterols (STs) dominate the mass of mitochondrial DRMs. Also, it has been proven that (i) the impact of salinity provokes obvious growth in the content of CERs in DRMs of chloroplasts; (ii) the content of STs in DRMs of chloroplasts does not change under the influence of NaCl; (iii) salinity also causes some elevation in the content of monounsaturated and saturated fatty acids (FAs). Considering the fact that DRMs represent integral parts of both chloroplast and mitochondrial membranes, the authors have come to the conclusion that the cells of euhalophyte S. perennans, under the impact of salinity, presumes the choice (by the cell) of some specific composition of lipids and FAs in the membrane. This may be considered as a specific protection reaction of the plant cell against salinity.

Prognostic of Yield of Potatoes of Promising Domestic Varieties under the Impact of Stress Abiotic Factors

Twenty-four potato (Solanum tuberosum L.) varieties differing in ripening groups (early, middle-early, and mid-season-ripening) were studied. Potatoes were grown under the conditions of the Middle Volga region of Russia in 2019-2021. It was found statistically that the yield (t/ha) of the early and mid-season-ripening varieties was negatively correlated with the increase in average temperatures during the growing season from May to August (R = -0.97, p = 0.04). Soil moisture content at a depth of 20 cm was positively correlated with the yield of middle-early varieties (R = 0.97, p = 0.04). The average tuber weight in the early varieties was sensitive to the increase in average temperatures (R = -0.95, p = 0.04). An increase in soil moisture content was beneficial to the average tuber weight (R = 0.98, p = 0.04), though only in the middle-early and mid-season-ripening groups. However, the soil moisture content and the tuber numbers in the mid-season-ripening varieties were negatively correlated (R = -0.96, p = 0.05).

Balance of Δ5-and Δ7-sterols and stanols in halophytes in connection with salinity tolerance

Sterols (STs) have a key role in regulating the fluidity and permeability of membranes in plants (phytosterols) that have wide structural diversity. We studied the effect of structural STs diversity on salt tolerance in halophytes. Specifically, we used gas chromatography-mass spectrometry (GC-MS), including two-dimensional gas chromatography-mass spectrometry (GCxGC-MS), to assess the STs composition in leaves of 21 species of wild-growing halophytes from four families (Asteraceae, Chenopodiaceae, Plumbaginaceae, Tamaricaceae) and three ecological groups (Euhalophytes (Eu), recretophytes (Re), salt excluders (Ex)). Fifteen molecular species of STs from three main groups, Δ⁵-, Δ⁷-and Δ⁰- STs (stanols), were detected. Plants of the genus Artemisia were characterized by a high content of stigmasterol (30-49% of the total STs), while β-sitosterol was the major compound in two Limonium spp., where it comprised 84-92% of the total STs. Species of Chenopodiaceae were able to accumulate both Δ⁵-and Δ⁷-STs and stanols. The content of the predominant Δ⁵-STs decreased in the order Ex → Re → Eu. Molecular species with a saturated steroid nucleus were identified in Eu and Re, suggesting their special salt-accumulating and salt-releasing functions. The structural analogues of stigmasterol, having a double bond C-22, were stigmasta-7,22-dien-3β-ol (spinasterol) and stigmast-22-en-3β-ol (Δ^7--sitosterol). The ratio of Δ⁵-stigmasterol/Δ⁵-β-sitosterol increased in Ex plants, and spinasterol/Δ^7--sitosterol and 22-stigmastenol/sitostanol increased in Eu plants. These data support the well-known role of stigmasterol and its isomers in plant responses to abiotic and biotic factors. The variability in STs types and their ratios suggested some involvement of the sterol membrane components in plant adaptation to growth conditions. The balance of Δ⁵-, Δ⁷-and stanols, as well as the accumulation of molecular analogues of stigmasterol, was suggested to be associated with salt tolerance of the plant species in this investigation.

Heterotrophic Microbiota from the Oligotrophic Waters of Lake Vostok, Antarctica

Lake Vostok is the deepest lake of Antarctica but has poor accessibility for study due to a thick glacial cover, however, water samples of this lake have become available for study just recently. Previously, only the microbiome of the ice cover samples was characterized. Here we report results of bacteriological seeding with subsequent identification of the heterotrophic microorganisms (bacteria and micellar fungi) present by 16S rDNA sequencing as well as results of a direct molecular study of the water microbiome. Surprisingly, the data obtained gave evidence of a predominant occurrence of common chemoorganotrophs that were rather psychrotolerant than psychrophilic. We isolated and described strains belonging to eight heterotrophic microbial species able to grow in a rich medium: six bacterial strains belonging to the species Microbacterium testaceum and Microbacterium trichothecenolyticum, Brevundimonas diminuta, Sphingomonas oligophenolica, Sphingomonas sp. and Sphingobium limneticum; and two fungal strains belonging to Dendryphion sp. and Cladosporium fusiforme. Direct study of 16S rDNA purified water samples confirmed the predominance of the Brevundimonas, Microbacterium, Bradyrhizobium, and Bacillus (Bacillus cereus) genera.

A novel efficient producer of human ω-amidase (Nit2) in Escherichia coli

Nit2/ω-amidase catalyzes the hydrolysis of α-ketoglutaramate (KGM, the α-keto acid analogue of glutamine) to α-ketoglutarate and ammonia. The enzyme also catalyzes the amide hydrolysis of monoamides of 4- and 5-C-dicarboxylates, including α-ketosuccinamate (KSM, the α-keto acid analogue of asparagine) and succinamate (SM). Here we describe an inexpensive procedure for high-yield expression of human Nit2 (hNit2) in Escherichia coli and purification of the expressed protein. This work includes: 1) the design of a genetic construct (pQE-Nit22) obtained from the previously described construct (pQE-Nit2) by replacing rare codons within an 81 bp-long DNA fragment "preferred" by E. coli near the translation initiation site; 2) methods for producing and maintaining the pQE-Nit22 construct; 3) purification of recombinant hNit2; and 4) activity measurements of the purified enzyme with KGM and SM. Important features of the hNit2 gene within the pQE-Nit22 construct are: 1) optimized codon composition, 2) the presence of an N-terminus His₆ tag immediately after the initiating codon ATG (Met) that permits efficient purification of the end-product on a Ni-NTA-agarose column. We anticipate that the availability of high yield hNit2/ω-amidase will be helpful in elucidating the normal and pathological roles of this enzyme and in the design of specific inhibitors.

Productivity and Dynamics of Morphological, Physiological, and Biochemical Parameters of Potatoes in Arid Climate

Interrelation between the morphology, physiology, biochemistry, and productivity of potato plants was shown for the first time using the example of a mid-season-ripening variety (v.) Siversky and a mid-early Tretyakovka v. The yield of Siversky v. turned out to be 1.6 times higher than the yield of Tretyakovka. Aboveground biomass of Siversky v. was distinguished by an increased content of photosynthetic pigments, a greater variability of the protein and lipid metabolism indicators, and more intense oxidation processes and antioxidant protection, which can be the key to its greater productivity. Multivariate statistical analysis showed that the greatest relationship in the climatic conditions of central Russia in 2020 was found for productivity and such indicators as the stomata number per unit leaf area, the number of stems, and the content of pigments, phospholipids, neutral lipids, and water-soluble part of the protein. Thus, both morphological and physiological-biochemical properties can influence the course and direction of the production process, and, hence, the yield of a certain variety.

Physiological and Biochemical Strategies of Adaptation in Halophytes

The relationship between the ecological adaptive strategies of some halophyte groups and their metabolism has been demonstrated; this correlation determines their competitive capabilities and place in the ecosystem. The features of the content of total and membrane lipids, chlorophylls, carotenoids, and membrane and water-soluble proteins, as well as the level of lipid peroxidation, hydration of photosynthetic organs, and sodium accumulation in euhalophytes, crynohalophytes, and glycohalophytes, which are confined to different levels of soil salinity, have been established.

Synthesis of 13С- and 14С-labeled linoleic acids for use in diagnostic breath tests for hepatobiliary system disorders

At present, there is a need for a simple, noninvasive, highly specific and sensitive diagnostic test for hepatobiliary system disorders. Compounds labeled with carbon isotopes are widely used in various diagnostic breath tests; they are safe and can reliably detect a metabolic disorder or enzyme deficiency. The aim of this study was to synthesize 13С- and 14С-labeled linoleic acids suitable for use in hepatobiliary breath tests in terms of purity. In the synthesis of 13С-labeled linoleic acid, the chemical yield for 1-bromo-8,11-heptadecadien was 86.4% and the chemical yield for barium carbonate-13С, 96.0%. In the synthesis of 14С-labeled linoleic acid, the chemical yield for 1-bromo-8,11-heptadecadien was 87.39%; for barium carbonate-14С it was 97.1%. The specific radioactivity of 14С-labeled linoleic acids was 45.36 ± 0.02 mCi/g. The radiochemical yield of the reaction was 96.0%. The proposed method is suitable for batch production.

Membrane-forming lipids of wild halophytes growing under the conditions of Prieltonie of South Russia

The composition of membrane-forming lipids has been examined for 10 wild halophyte species growing in southern Russian on alkaline soil. The plants belong to seven taxa of family rank: by their life form, which are semi-shrubs, herbaceous annuals, and perennial plants; their salt tolerance, which are classified as the euhalophytes, crynohalophytes, and glycohalophytes; and by their sensitivity to water, classifications of mesoxerophytes and xeromesophytes. Parallels have been found between the lipid composition and the ecological status of the plants. It has also been revealed that the similarity in the glyco- and phospholipid composition of different plant groups relates to the water factor and the type of salt accumulation, respectively. The fatty acid compositions of the examined plants is determined at the species level.

[Polar lipid pool modification in leaves of hoary plantain (Plantago media L.) plants during their light adaptation under natural conditions]

Polar glycerolipids and photosynthetic pigments of Plantago media L. plants, growing on limestone outcrops of the Southern Timan, have been studied. Leaves of plants growing on well insolated and heated slopes are characterized by an intensive lipoperoxidation; the accumulation of chlorophylls and carotenoids in these plants is 1.5-2 times less and the content of polar lipids is 15-20% less than in plants growing in dense grass at the bottom of slopes. The accumulation of some classes of glycerolipids in leaves in the daytime provides for stabilization of photosystem complexes and the formation of the pool of zeaxanthin, a protective xanthophyll. Changes in the content and ratio of lipids represent an important part of the adaptive reorganizations of the photosynthetic apparatus caused by excess radiation under natural conditions.

[Regulation of gene expression in type II restriction-modification system]

Type II restriction-modification systems are comprised of a restriction endonuclease and methyltransferase. The enzymes are coded by individual genes and recognize the same DNA sequence. Endonuclease makes a double-stranded break in the recognition site, and methyltransferase covalently modifies the DNA bases within the recognition site, thereby down-regulating endonuclease activity. Coordinated action of these enzymes plays a role of primitive immune system and protects bacterial host cell from the invasion of foreign (for example, viral) DNA. However, uncontrolled expression of the restriction-modification system genes can result in the death of bacterial host cell because of the endonuclease cleavage of host DNA. In the present review, the data on the expression regulation of the type II restriction-modification enzymes are discussed.

[Mercury-resistant bacteria from permafrost sediments and prospects for their use in comparative studies of mercury resistance determinants]

Mercury-resistant bacteria were isolated from permafrost sediments of Kolyma lowland and Canada existing over five thousand to two million years. Their content was shown to vary within the range 0.001-2.9% and to depend on the amount of mercury in sampling sites (coefficient of correlation 0.75). A collection of mercury-resistant bacterial strains was created. In this collection, various representatives of both Gram-positive bacteria (Bacillus, Exiguobacterium, Micrococcus, Arthrobacter) and Gram-negative bacteria (Pseudomonas, Acinetobacter, Plesiomonas, Myxobacteriales) were identified. Most resistant bacteria were found to contain determinants homologous to mer-operons of contemporary bacteria. The isolated strains of paleobacteria are proposed to be used for a comparative structural study of contemporary and ancient plasmids and transposons carrying mercury resistance determinants.

[Horizontal transfer of mercury resistance genes in natural bacterial populations]

The results of studying the horizontal transfer of mercury resistance determinants in environmental bacterial populations are reviewed. Identical or highly homologous mercury resistance (mer) operons and transposons were found in bacteria of different taxonomic groups from geographically distant regions. Recombinant mer operons and transposons were revealed. The data suggest high frequencies of horizontal transfer and of recombination for mercury resistance determinants. The mechanisms of horizontal gene transfer were elucidated in Gram-negative and Gram-positive bacteria. New transposons were found and analyzed.

Horizontal spread of mer operons among gram-positive bacteria in natural environments

Horizontal dissemination of the genes responsible for resistance to toxic pollutants may play a key role in the adaptation of bacterial populations to environmental contaminants. However, the frequency and extent of gene dissemination in natural environments is not known. A natural horizontal spread of two distinct mercury resistance (mer) operon variants, which occurred amongst diverse Bacillus and related species over wide geographical areas, is reported. One mer variant encodes a mercuric reductase with a single N-terminal domain, whilst the other encodes a reductase with a duplicated N-terminal domain. The strains containing the former mer operon types are sensitive to organomercurials, and are most common in the terrestrial mercury-resistant Bacillus populations studied in this work. The strains containing the latter operon types are resistant to organomercurials, and dominate in a Minamata Bay mercury-resistant Bacillus population, previously described in the literature. At least three distinct transposons (related to a class II vancomycin-resistance transposon, Tn1546, from a clinical Enterococcus strain) and conjugative plasmids are implicated as mediators of the spread of these mer operons.

Mercuric reductase in environmental gram-positive bacteria sensitive to mercury

According to existing data, mercury resistance operons (mer operons) are in general thought to be rare in bacteria, other than those from mercury-contaminated sites. We have found that a high proportion of strains in environmental isolates of Gram-positive bacteria express mercuric reductase (MerA protein): the majority of these strains are apparently sensitive to mercury. The expression of MerA was also inducible in all cases. These results imply the presence of phenotypically cryptic mer resistance operons, with both the merA (mercuric reductase) and merR (regulatory) genes still present, but the possible absence of the transport function required to complete the resistance mechanism. This indicates that mer operons or parts thereof are more widely spread in nature than is suggested by the frequency of mercury-resistant bacteria.

Occurrence of two structural types of mercury reductases among gram-positive bacteria

Structural variants of mercury reductase containing the N-terminal domain, which is easily cleaved by trypsin, have been found in Gram-positive bacteria with a low genomic G + C content (Bacillus, Staphylococcus and, possibly, some other genera). Mercury reductases without the N-terminal domain and relatively resistant to limited proteolysis are typical for Gram-positive bacteria with a high genomic G + C content (Arthrobacter, Citreobacterium, Micrococcus, Mycobacterium, Rhodococcus). Both types of mercury reductase genes may be located on plasmids.

Two structural types of mercury reductases and possible ways of their evolution

Structural differences have been revealed among mercury reductases of immunologically unrelated types from Gram-positive bacteria: enzymes of one immunological type have a molecular mass of 62-69 kDa and seem to contain an N-terminal extension of 5-15 kDa, which is easily cleaved by trypsin and chymotrypsin; enzymes of the other immunological type have a molecular mass of 52-57 kDa and are resistant to proteolysis. The existence of at least two different lines in the evolution of mercury reductases is surmised.

[Study of the horizontal transfer of mercury resistance genes in natural populations of bacteria using antibodies to mercury reductases]

Mercury resistant soil and intestinal bacteria were isolated from different mercury deposit areas of the USSR. Mercury reductases from all gram negative bacteria studied (Pseudomonas, Acinetobacter and Enterobacterial species) with a single exception (Flavobacterium sp.) were immunologically cross reactive. Two immunological types of mercury reductases were found among gram positive bacteria (Bacillus, Staphylococcus and Coryneform species). Further subdivisions were done by "spur" formation tests. Despite considerable diversity of mercury reductases revealed in this study, we found several strains which belonged to distant genera but contained immunologically indistinguishable enzymes. This suggested that the horizontal spread of the corresponding genes occurred in these genera in relatively recent time.

The diversity of mercury reductases among mercury-resistant bacteria

Two immunologically non-cross-reactive types of mercury reductases were found among Gram-negative and two among Gram-positive mercury-resistant environmental bacteria. Mercury reductases were further discriminated by 'spur' formation immunodiffusion tests. Immunologically indistinguishable mercury reductases were found among strains belonging to phylogenetically distant genera. This suggests a horizontal transfer of mercury resistance genes between these strains.

[Histone H1, polylysine and spermine--factors of nucleosome assembly in vitro]

We studied nucleosome assemble in vitro in a system containing the relaxed DNA CoIE1, core histones and a crude extract Drosophila embryos. Supercoiling is a criterium for making conclusions about forming nucleosomes. Supercoiling raises more if nucleosome assemble takes place in the presence of histone H1, polylysine of the 20 000 molecular weight or spermine. These agents do not stimulate the relaxation, and they are more effective when they are added earlier. Thus histone H1, spermine and polylysine can facilitate nucleosome assemble in vitro and with two former agents it may be possibly that the same process takes place in vivo.

H1 histone, polylysine and spermine facilitate nucleosome assembly in vitro

Nucleosome formation has been studied in a system containing relaxed Col E1 DNA, core histones and an extract of Drosophila embryos. The formation of nucleosomes was established by the introduction of supercoils into DNA. The degree of DNA supercoiling was shown to be higher if nucleosomes were assembled in the presence of the H1 histone, polylysine (Mr 20 000) or spermine. These agents do not stimulate relaxation and are the more effective the earlier they are added to the reaction. Thus, the H1 histone, polylysine and spermine facilitate nucleosome assembly in vitro.

[Interactions of subunits of DNA gyrase]

Interaction of DNA gyrase A- and B-subunits during the process of DNA supercoiling was studied. For this purpose a E. coli Cour-1 mutant resistant to coumermycin and containing a mutation in the B-subunit of DNA gyrase was isolated and the influence of the DNA gyrase A-subunit specific inhibitor-nalidixic acid-on DNA supercoiling by wild-type and mutant enzymes was investigated. It turned out that the enzyme from the Cour-1 mutant strain was more sensitive to nalidixic acid than the DNA gyrase from the wild-type strain. Hence, the mutation affecting the B-subunit is capable to change A-subunit properties. That makes it possible to draw the conclusion about a close structural interaction of DNA gyrase subunits during DNA supercoiling.

Changed properties of the A subunit in DNA gyrase with a B subunit mutation

To investigate the interaction of subunits A and B of DNA gyrase during DNA supercoiling, a Cour mutant of Escherichia coli was obtained and the effect of nalidixic acid on the supercoiling of DNA by wild-type and mutant enzymes was assayed. The enzyme of the Cour strain proved to be more sensitive to nalidixic acid than the wild-type DNA gyrase. Hence the mutation affecting the B subunit can also change the properties of the A subunit, which fact suggests that the two subunits of DNA gyrase are in contact during DNA supercoiling.

DNA supercoiling and transcription in Escherichia coli: influence of RNA polymerase mutations

Coumermycin A1, a specific inhibitor of DNA gyrase, differentially changes the spectrum of proteins synthesized in wild type E. coli cells but has no effect on the protein spectrum in mutant cells with coumermycin-resistant DNA gyrase. The rpoB265 mutation affecting RNA polymerase decreases the coumermycin A1-sensitivity of bacteria while the rpoC3 mutation increases it. The interaction of wild type and mutant RpoB265 RNA polymerases with ColEl plasmid DNA in vitro is differently affected by DNA supercoiling. No such differences are observed in the case of RpoC3 RNA polymerase. The results suggest that template supercoiling may have a substantial effect on transcription in vivo, an effect which, in some cases, depends on the properties of RNA polymerase.

[Effect of DNA supercoiling on transcription performed by normal and mutant Escherichia coli RNA-polymerases]

A specific DNA-gyrase, inhibitor, coumermycin A1, causes differential changes in the spectrum of proteins synthesized in E. coli wild types cells, while protein spectrum in the mutant cells with coumermycin-resistant DNA-gyrase is left unaffected. The mutation of RNA-polymerase RpoB265 lowers the sensitivity of bacteria to coumermycin A1, whereas the RpoC3 enhances it. The differences between the normal and mutant RpoB265 RNA polymerases on interaction in vitro with ColE1 DNA plasmid depend on its supercoiling. No dependences of this kind were detected when comparing the normal and RpoC3-RNA polymerase. The obtained data indicate that the template supercoiling may significantly affect the transcription in vivo and that the properties of RNA polymerase may in some cases define this influence.