V. K. Akimenko

Involvement of the respiratory chain of gram-negative bacteria in the reduction of tellurite.

Abstract. The terminal oxidases of the respiratory chain of seven strains of gram-negative bacteria were shown to be involved in the reduction of tellurite. The rate of tellurite reduction correlated with the intensity of respiration. The inhibitors of terminal oxidases, carbon monoxide and cyanide, inhibited the reduction of tellurite. In Pseudomonas aeruginosa PAO ML4262 and P. aeruginosa PAO ML4262 (pBS10), the respiratory chain was found to contain three types of cytochrome c, one of which (the carbon monoxide-binding cytochrome c) was involved in the reduction of tellurite. Agrobacterium tumefaciens VKM B-1219, P. aeruginosa IBPM B-13, and Escherichia coli G0-102bd++ cells contained oxidases aa3, bb3, and bd, respectively. The respiratory chain of other strains contained two oxidases: E. coli DH5α of bb3- and bd-type, and Erwinia carotovora VKM B-567 of bo3- and bd-type. All the strains under study reduced tellurite with the formation of tellurium crystallites. Depending on the position of the active center of terminal oxidases in the plasma membrane, the crystallites appeared either in the periplasmic space [P. aeruginosa PAO ML4262 and P. aeruginosa PAO ML4262 (pBS10)], or on the outer surface of the membrane (A. tumefaciens VKM B-1219 and P. aeruginosa IBPM B-13), its inner surface (E. coli G0-102bd++), or on both surfaces (E. coli DH5α and E. carotovora VKM B-567).

Biosynthesis of Naphthoquinone Pigments by Fungi of the Genus Fusarium

We studied the biosynthesis of colored naphthoquinone metabolites by Fusarium decemcellulare, F. graminearum, and F. bulbigenum fungi. Depending on the conditions of cultivation, F. bulbigenum and F. graminearum synthesized bikaverin and aurofusarin, respectively, whereas F. decemcellulare synthesized soluble extracellular naphthoquinones of the naphthazarin structure (javanicin, anhydrojavanicin, fusarubin, anhydrofusarubin, bostricoidin, and novarubin) or extracellular dimeric naphthoquinone aurofusarin. The biosynthesis of naphthoquinone pigments was shown to be the main response of the fungi to stress, observed under conditions of growth inhibition or arrest.

Tolerance of the yeast Yarrowia lipolytica to oxidative stress

The adaptive response of the yeast Yarrowia lipolytica to the oxidative stress induced by the oxidants hydrogen peroxide, menadione, and juglone has been studied. H2O2, menadione, and juglone completely inhibited yeast growth at concentrations higher than 120, 0.5, and 0.03 mM, respectively. The stationary-phase yeast cells were found to be more resistant to the oxidants than the exponential-phase cells. The 60-min pretreatment of logarithmic-phase cells with nonlethal concentrations of H2O2 (0.3 mM), menadione (0.05 mM), and juglone (0.005 mM) made the cells more resistant to high concentrations of these oxidants. The adaptation of yeast cells to H2O2, menadione, and juglone was associated with an increase in the activity of cellular catalase, superoxide dismutase, glucose-6-phosphate dehydrogenase, and glutathione reductase, the main enzymes involved in cell defense against oxidative stress.

Adaptation of the Phytopathogenic Fungus Fusarium decemcellulare to Oxidative Stress

The adaptive response of the phytopathogenic fungus Fusarium decemcellulare to the oxidative stress induced by hydrogen peroxide and juglone (5-hydroxy-1,4-naphthoquinone) was studied. At concentrations higher than 1 mM, H2O2 and juglone completely inhibited the growth of the fungus. The 60-min pretreatment of logarithmic-phase cells with nonlethal concentrations of H2O2 (0.25 mM) and juglone (0.1 mM) led to the development of a resistance to high concentrations of these oxidants. The stationary-phase cells were found to be more resistant to the oxidants than the logarithmic-phase cells. The adaptation of fungal cells to H2O2 and juglone was associated with an increase in the activity of cellular catalase and superoxide dismutase, the main enzymes involved in the defense against oxidative stress.

Isoprenoid Pigments in Representatives of the Family Microbacteriaceae

By using fosmidomycin and mevinolin (inhibitors of the synthesis of isoprenoid pigments), spectrophotometry, and mass spectrometry, the presence of isoprenoid pigments is shown in 71 of the 78 strains under study. All of these strains belong to 11 genera of the family Microbacteriaceae. Yellow, orange, and red pigments are found to have absorption spectra typical of C40-carotenoids. Eight out of the sixteen strains of the genus Microbacterium are able to synthesize neurosporene, a precursor of lycopene and β-carotene. The biosynthesis of carotenoids in some representatives of the genera Agromyces, Leifsonia, and Microbacterium is induced by light. Inhibition of the biosynthesis of isoprenoid pigments by fosmidomycin suggests that they are synthesized via the nonmevalonate pathway. Twelve strains are found to exhibit both the nonmevalonate and mevalonate pathways of isoprenoid synthesis. These data, together with the difference in the inhibitory concentration of fosmidomycin, can be used for differentiating various taxa within the family Microbacteriaceae.

Distribution of cyanide-resistant respiration among yeasts and bacteria and its relation to oversynthesis of metabolites

The prevalence of cyanide-resistant respiration among yeasts and bacteria and its relation to oversynthesis of metabolites was studied. It was shown that cyanide-resistant respiration was characteristic of most microorganisms under study. In reference to yeasts this ability was observed in those with aerobic type of metabolism. The cyanide resistant respiration appeared during retardation or complete cessation of microbial growth provided there was no oversynthesis of metabolites. If the retardation or cessation of growth was accompanied by the induction of the oversynthesis of metabolites it led to inhibition of the development of the cyanide-resistant respiration. We came to the conclusion that there are competitive relations between the oversynthesis of metabolites and cyanide-resistant respiration exactly as they are between the two processes directed to the release of excessive energy.

Adaptation of the yeast Yarrowia lipolytica to heat shock

The adaptive response of the yeast Yarrowia lipolytica to heat shock has been studied. Experiments showed that, after 10 min of incubation at 45°C, the survival rate of Yarrowia lipolytica cells was less than 0.1%. Stationary-phase yeast cells were found to be more thermotolerant than exponential-phase cells. A 60-min preincubation of cells at 37°C or pretreatment with low concentrations of H2O2 (0.5 mM) or menadione (0.05 mM) made them more tolerant to heat and to oxidative stress (120 mM hydrogen peroxide). The pH dependence of yeast thermotolerance has also been studied. The adaptation of yeast cells to heat shock and oxidative stress was found to be associated with a decrease in the intracellular level of cAMP and an increase in the activity of antioxidant enzymes (catalase, superoxide dismutase, glucose-6-phosphate dehydrogenase, and glutathione reductase).

Unsaturated organic acids as terminal electron acceptors for reductase chains of anaerobic bacteria

This paper summarizes the current knowledge of unsaturated organic acids in their role as terminal electron acceptors for reductase chains of anaerobic bacteria. The mechanisms and enzyme systems involved in the reduction of fumarate by Escherichia coli, Wolinella succinogenes, and some species of the genus Shewanella are considered. Particular attention is given to reduction of the double bond of the unnatural compound methacrylate by the δ-proteobacterium Geobacter sulfurreducens AM-1. Soluble periplasmic flavocytochromes c, found in bacteria of the genera Shewanella and Geobacter, are involved in the hydrogenation of fumarate (in Shewanella species) and methacrylate (in G. sulfurreducens AM-1). In E. coli and W. succinogenes, fumarate is reduced in cytosol by membrane-bound fumarate reductases. The prospects for research into organic acid reduction at double bonds in bacteria are discussed.

Isolation and characterization of a new low-molecular antibacterial peptide of the lantibiotics family

The physicochemical and biological properties of the low-molecular antibacterial peptide isolated from the cultivation medium of Staphylococcus warneri IEGM KL-1 were studied. The peptide was obtained in a homogenous state by the methods of ultrafiltration, ion exchange, and reversed phase chromatography. The peptide contained a substantial quantity of cationic and hydrophobic amino acid residues and an uncommon amino acid lanthionine. The molecular mass of the peptide was 2999 Da. A bactericidal effect of the isolated peptide on the cells of S. epidermidis 33 was exhibited in a wide pH range, being completely preserved upon heat treatment. In accordance with the characteristics, origin, and species affiliation of the producer, the peptide was named warnerin. The available data allow us to consider warnerin as a new representative of the family of lantibiotics, promising antibiotic agents of microbial origin.

Respiratory activity of yeast Yarrowia lipolytica under oxidative stress and heat shock

Heat shock (45°C) and the effect of oxidants (H2O2) resulted in a decrease of the respiratory activity of yeast cells and their survival rate. Increased resistance to stress effects after mild heat treatment (37°C) or treatment with a nonlethal dose of oxidants (0.5 mM H2O2) for 60 min) was accompanied by appearance of an alternative (cyanide-resistant) oxidative pathway in the mitochondria, which promotes survival due to retention of the capacity for ATP synthesis in the first coupling point at the level of endogenous NADH dehydrogenase. The alternative oxidative pathway is more resistant to the effect of stressors that disrupt electron transfer in the cytochrome site of the respiratory chain.