Cytoplasmic inorganic polyphosphate participates in the heavy metal tolerance of Cryptococcus humicola

The basidiomycetous yeast Cryptococcus humicola was shown to be tolerant to manganese, cobalt, nickel, zinc, lanthanum, and cadmium cations at a concentration of 2.5 mmol/L, which is toxic for many yeasts. The basidiomycetous yeast Cryptococcus terreus was sensitive to all these ions and did not grow at the above concentration. In the presence of heavy metal cations, С. humicola, as opposed to C. terreus, was characterized by the higher content of acid-soluble inorganic polyphosphates. In vivo 4′,6′-diamino-2-phenylindole dihydrochloride staining revealed polyphosphate accumulation in the cell wall and cytoplasmic inclusions of С. humicola in the presence of heavy metals. In C. terreus, polyphosphates in the presence of heavy metals accumulate mainly in vacuoles, which results in morphological changes in these organelles and, probably, disturbance of their function. The role of polyphosphate accumulation and cellular localization as factors of heavy metal tolerance of Cryptococcus humicola is discussed.     

Defects in the leptin axis reduce abundance of the ABCG5-ABCG8 sterol transporter in liver

ABGG5 (G5) and ABCG8 (G8) are ABC half-transporters that dimerize within the endoplasmic reticulum, traffic to the cell surface, and mediate cholesterol excretion into bile. Mice harboring defects in the leptin axis (db/db and ob/ob) have reduced biliary cholesterol concentrations. Rapid weight loss brought about by administration of leptin or dietary restriction increases biliary cholesterol excretion. We hypothesized that the reduction in biliary cholesterol in mice harboring defects in the leptin axis is associated with a reduction in G5G8 transporters and that levels of the transporter would increase with leptin administration and dietary restriction. We examined mRNA and protein levels for G5 and G8 in db/db and ob/ob mice. In both models G5 and G8 protein levels were reduced. In ob/ob mice, both leptin administration and dietary restriction increased G5 and G8 protein and biliary cholesterol concentrations. Finally, we examined the effects of tauroursodeoxycholate, which has been shown to increase biliary cholesterol excretion and function as a molecular chaperone. Tauroursodeoxycholate increased G5 and G8 protein and biliary cholesterol concentrations in both wild-type and db/db mice. Our results indicate that the mechanism for reduced biliary cholesterol excretion in db/db and ob/ob mice involves reductions in G5 and G8 protein levels and that this may occur at the level of G5G8 heterodimer assembly within the endoplasmic reticulum.     

Enhanced resistance to peroxide stress in Escherichia coli grown outside their niche temperatures

Extended exposure of Escherichia coli to temperatures above and below their growth optimum led to significant changes in oxidant production and antioxidant defense. At 20 °C an increase in the intracellular H₂O₂ concentration and oxidized glutathione (GSSG) level was observed against a background of low levels of reduced glutathione (GSH) and decreased catalase and glutathione reductase (GOR) activities. The intracellular H₂O₂ and GSSG concentrations had minimal values at 30 and 37 °C, but rose again at 42 °C, suggesting that oxidative processes were intensified at high temperatures. An increase in temperature from 20 to 42 °C led to an elevation in the oxygen respiration rate and superoxide production; a 5-fold increase in the intracellular GSH concentration and in the GSH:GSSG ratio occurred simultaneously. Catalase HPI and GOR activities were elevated 4.4- and 1.5-fold, respectively. Prolonged exposure to sublethal temperatures facilitated an adaptation to subsequent oxidative stress produced by the addition of H₂O₂.     

Changes in the biota of Chany Lake along a salinity gradient

Relationships among salinity and diversity, abundance, biomass of major biological components of Chany Lake (western Siberia, Russia) are examined across a salinity gradient. As salinity increased from 0.8 to 6.4 g l⁻¹, the species richness of aquatic vascular plants decreased from 16 to 2 species, of phytoplankton from 98 to 52 species, and of zooplankton from 61 to 16 species, but changes in species diversity of zoobenthos were negligible. Guest Editor: John M. Melack Saline Waters and their Biota     

Seasonal dynamics of long-chain polyunsaturated fatty acids in littoral benthos in the upper Yenisei river

We studied composition and concentrations of fatty acids (FAs) in benthos from pebbly littoral region of the Yenisei River in a sampling site near Krasnoyarsk city (Siberia, Russia) for 1 year from March 2003 to February 2004. Special attention was paid to major long-chain polyunsaturated fatty acids (PUFAs) of the ω3 family: eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acids (DHA, 22:6ω3). In phytobenthos, which was dominated by diatoms, the annual maxima of EPA and DHA pool occurred in spring and early summer. In zoobenthos, EPA and DHA pool peaked in autumn, due mainly to an increase of the biomass of dominant taxa (gammarids) and to a moderate increase of the PUFA content per body weight. Seasonal peaks of EPA in overwintering insect larvae (chironomids and caddisflies) generally coincided with those of biomass of these larvae, while there was no such trend for amphipods and oligochaetes. In spring and early summer, the main part of ω3 PUFA, 40–97% of total amount, in the littoral region was contained in biomass of producers, i.e., benthic microalgae, and in autumn it was transferred to primary consumers—benthic invertebrates, which contained ∼76–93% of total ω3 PUFAs.     

N.BspD6I DNA nickase strongly stimulates template-independent synthesis of non-palindromic repetitive DNA by Bst DNA polymerase

Highly efficient DNA synthesis without template and primer DNAs occurs when N.BspD6I DNA nickase is added to a reaction mixture containing deoxynucleoside triphosphates and the large fragment of Bst DNA polymerase. Over a period of 2 h, virtually all the deoxynucleoside triphosphates (dNTPs) become incorporated into DNA. Inactivation of N.BspD6I nickase by heating inhibits DNA synthesis. Optimal N.BspD6I activity is required to achieve high yields of synthesized DNA. Electron microscopy data revealed that the majority of DNA molecules have a branched structure. Cloning and sequencing of the fragments synthesized demonstrated that the DNA product mainly consists of multiple hexanucleotide non-palindromic tandem repeats containing nickase recognition sites. A possible mechanism is discussed that addresses template-independent DNA synthesis stimulated by N.BspD6I nickase.     

Phylogenetic diversity in sulphate-reducing bacterial communities from oxidised and reduced bottom sediments of the Barents Sea

In the bottom sediments from a number of the Barents Sea sites, including coastal areas of the Novaya Zemlya, Franz Josef Land, and Svalbard archipelagos, sulphate reduction rates were measured and the phylogenetic composition of sulphate-reducing bacterial (SRB) communities was analysed for the first time. Molecular genetic analysis of the sequences of the 16S rRNA and dsrB genes (the latter encodes the β-subunit of dissimilatory (bi)sulphite reductase) revealed significant differences in the composition of bacterial communities in different sampling stations and sediment horizons of the Barents Sea depending on the physicochemical conditions. The major bacteria involved in reduction of sulphur compounds in Arctic marine bottom sediments belonged to Desulfobulbaceae, Desulfobacteraceae, Desulfovibrionaceae, Desulfuromonadaceae, and Desulfarculaceae families, as well as to uncultured clades SAR324 and Sva0485. Desulfobulbaceae and Desulfuromonadaceae predominated in the oxidised (E_h = 154–226 mV) upper layers of the sediments (up to 9% and 5.9% from all reads of the 16S rRNA gene sequences in the sample, correspondingly), while in deeper, more reduced layers (E_h = ?210 to ?105 mV) the share of Desulfobacteraceae in the SRB community was also significant (up to 5%). The highest relative abundance of members of Desulfarculaceae family (3.1%) was revealed in reduced layers of sandy-clayey sediments from the Barents Sea area affected by currents of transformed (mixed, with changed physicochemical characteristics) Atlantic waters.

     

Rational Design of ssODN to Correct Mutations by Gene Editing

Biochemistry (Moscow) - Gene editing allows to make a variety of targeted changes in genome, which can potentially be used to treat hereditary human diseases. Despite numerous studies in this area,...     

Mechanism of heat stress-induced cellular senescence elucidates the exclusive vulnerability of early S-phase cells to mild genotoxic stress

Heat stress is one of the best-studied cellular stress factors; however, little is known about its delayed effects. Here, we demonstrate that heat stress induces p21-dependent cellular senescence-like cell cycle arrest. Notably, only early S-phase cells undergo such an arrest in response to heat stress. The encounter of DNA replication forks with topoisomerase I-generated single-stranded DNA breaks resulted in the generation of persistent double-stranded DNA breaks was found to be a primary cause of heat stress-induced cellular senescence in these cells. This investigation of heat stress-induced cellular senescence elucidates the mechanisms underlying the exclusive sensitivity of early S-phase cells to ultra-low doses of agents that induce single-stranded DNA breaks.