Mutant yeast strains with altered sensitivity to heavy metals are crucial for revealing the mechanisms of metal absorption and detoxification, as well as for bioremediation of these pollutants. Here, we show that a knockout of the PHO87 gene encoding the low-affinity phosphate transporter of the cytoplasmic membrane of S. cerevisiae increased resistance to manganese, silver, and vanadate ions. However, a knockout of PHO90 (PHO87 paralog) did not affect the sensitivity to silver and vanadate ions but increased sensitivity to manganese ions. The Δpho87 cells accumulated 10 times less manganese compared to the wild-type cells, while the Δpho90 cells accumulated two times more manganese compared to the wild-type cells, when grown in YPD with 2 mM MnSO4. The polyphosphate content of the Δpho84, Δpho87, and Δpho90 cells cultivated at high phosphate concentration did not differ from that of the wild-type strain. In the presence of 2 mM MnSO4, Δpho87 cells contained several times less polyphosphates, and Δpho90 cells contained more short-chain polyphosphates than the cells of the wild-type strain. We hypothesize that phosphate carriers participate in the regulation of heavy metal uptake, and the respective knockouts are useful in bioremediation and bioassay of these pollutants.

Inorganic polyphosphates and respective metabolic pathways and enzymes are important factors for yeast active growth in unfavorable conditions. However, particular proteins of polyphosphate metabolism remain poorly explored in this context. Here we report biochemical and transcriptomic characterization of the CRN/PPN2 yeast strain (derived from Ppn1-lacking CRN strain) overexpressing poorly studied Ppn2 polyphosphatase. We showed that Ppn2 overexpression significantly reduced lag phase in the alkaline medium presumably due to the ability of Ppn2 to efficiently hydrolyze inorganic polyphosphates and thus neutralize hydroxide ions in the cell. With RNA-Seq, we compared the molecular phenotypes of CRN/PPN2 and its parent CRN strain grown in YPD or alkaline medium and detected transcriptomic changes induced by Ppn2 overexpression and reflecting the adaptation to alkaline conditions. The core set of upregulated genes included several genes with a previously unknown function. Respective knockout strains (∆ecm8, ∆yol160w, ∆cpp3, ∆ycr099c) exhibited defects of growth or cell morphology in the alkaline medium, proving the functional involvement of the respective proteins in sustaining growth in alkaline conditions.

Abstract Yeast cells possess high levels of inorganic polyphosphate, which is involved in various processes regulating vital activities. In this work, using the commercially available Saccharomyces cerevisiae knockout mutants in the PPN1 and PPN2 genes encoding polyphosphatases, we have shown that each of the two single mutations leads to a set of similar physiological effects at the stationary stage of growth on glucose: the increased resistance to manganese and peroxide stresses, lack of polyphosphatase activity in mitochondria, and the increase in long-chained polyphosphate level. We suggest, that the increased stress resistance of ∆ppn1 and ∆ppn2 strains is associated with the increase in the level of long-chained polyphosphate. The cells of ∆ppn1 and ∆ppn2 mutants showed no significant differences in growth parameters in the media with ethanol or glucose compared to the parent strain. Earlier, we observed the inability to grow on non-fermentable carbon sources and mitochondrial defects in the ∆ppn1 mutant CRN constructed from another parent strain. The ∆ppn1 strain from the Dharmacon collection has no defects in mitochondria function. The data obtained provide evidence in favor of the participation of polyphosphates in stress adaptation of yeast cells.

The CYSTM (cysteine-rich transmembrane module) protein family comprises small molecular cysteine-rich tail-anchored membrane proteins found in many eukaryotes. The Saccharomyces cerevisiae strains carrying the CYSTM genes YDRO34W-B and YBR056W-A (MNC1) fused with GFP were used to test the expression of these genes under different stresses. The YBR056W-A (MNC1) and YDR034W-B genes are expressed under stress conditions caused by the toxic concentrations of heavy metal ions, such as manganese, cobalt, nickel, zinc, cuprum, and 2.4-dinitrophenol uncoupler. The expression level of YDR034W-B was higher than that of YBR056W-A under alkali and cadmium stresses. The Ydr034w-b-GFP and Ybr056w-a-GFP proteins differ in the cellular localization: Ydr034w-b-GFP was mainly observed in the plasma membrane and vacuolar membrane, while Ybr056w-a-GFP was observed in the cytoplasm, probably in intracellular membranes. The null-mutants in both genes demonstrated decreased cell concentration and lytic phenotype when cultivated in the presence of excess manganese. This allows for speculations about the involvement of Mnc1 and Ydr034w-b proteins in manganese stress overcoming.

Inorganic polyphosphate (polyP) is an important factor in the stress resistance of microorganisms. The polyphosphate-overexpressing strains of yeast S. cerevisiae were used as a model for studying the inter-relationship between stress resistance and polyP level. We compared the polyP level and resistance to the oxidative, manganese, cadmium, and alkaline stresses in parent stain CRN and in strains overexpressing the four yeast polyphosphatases: Ppx1, Ppn1, Ppn2, and Ddp1. Strains overexpressing Ppx1, Ppn1, and Ppn2 have lower polyP content and the strain overexpressing Ddp1 has the same polyP content as the parent strain. The strains overexpressing Ppn1 and Ddp1 show higher resistance to peroxide and manganese. The strain overexpressing Ppx1 showed a decrease in peroxide resistance. The strain overexpressing Ppn2 was more resistant to alkaline and peroxide stresses. A similar increase in resistance to the manganese and peroxide stresses of strains overexpressing Ppn1 and Ddp1, which differ in polyP content, led to the conclusion that there is no direct relationship between polyP content and variations in this resistance. Thus, we speculate about the potential role of inositol pyrophosphates as signaling molecules in stress response.

Inorganic polyphosphates (polyP) are the linear polymers of orthophosphoric acid varying in the number of phosphate residues linked by the energy-rich phosphoanhydride bonds. PolyP is an essential component in living cells. Knowledge of polyP metabolizing enzymes in eukaryotes is necessary for understanding molecular mechanisms of polyP metabolism in humans and development of new approaches for treating bone and cardiovascular diseases associated with impaired mineral phosphorus metabolism. Yeast cells represent a rational experimental model for this research due to availability of the methods for studying phosphorus metabolism and construction of knockout mutants and strains overexpressing target proteins. Multicomponent system of polyP metabolism in Saccharomyces cerevisiae cells is presented in this review discussing properties, functioning, and practical significance of the enzymes involved in the synthesis and degradation of this important metabolite.

Saccharomyces cerevisiae has high level of inorganic polyphosphate and a multicomponent system of its metabolism, including polyphosphatases Ppx1, Ppn1, Ddp1, and Ppn2. The aim of the study was to construct the yeast strain overexpressing Ppn2 and to compare the properties of Ppn2, Ppx1, Ppn1, and Ddp1 purified from overexpressing strains of S. cerevisiae. We overexpressed Ppn2 in S. cerevisiae under a strong constitutive promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase-encoding gene and suggested biochemical criteria for distinguishing among yeast polyphosphatases, which is important for their identification and understanding of their functions. Ppn2, Ppn1, and Ddp1 had endopolyphosphatase activities, whereas Ppx1 did not. Ppx1 and Ppn1 exhibited high and Ddp1 and Ppn2 low exopolyphosphatase activity: 240, 500, 0.05 and 0.1 U/mg protein, respectively. The enzymes had distinct patterns of exopolyphosphatase activities stimulation by divalent metal ions. Ppn2, Ppn1 and Ddp1 displayed endopolyphosphatase activity in the presence of 1 mM Mg2+. The endopolyphosphatase activities of Ppn2 and Ppn1 were induced by 0.01 mM of Co(2+)or Zn2+, whereas that of Ddp1 required 0.1 mM of these cations. The endopolyphosphatase activity of Ppn1 was inhibited by 0.01 mg mL(-1) of heparin, while endopolphosphatase activity of Ppn2 was weakly sensitive to 0.25 mg mL(-1) of heparin. The Ppx1 and Ppn1 activity with guanosine tetraphosphate was nearly 80% of activity with long-chain polyphosphates. The Ppn1 hydrolyzed dATP, while Ppx1 did not. The differences in the mode of polyphosphate hydrolysis, substrate specificity, metal ion dependence and cell localization suggest distinct roles of these enzymes in yeast. (C) 2019 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.

Inorganic polyphosphate (polyP) is a significant regulatory and metabolic compound in yeast cells. We compared polyP content and localization, polyphosphatase activities, and transcriptional profile of polyP-related genes in industrially important methylotrophic yeasts, Hansenula polymorpha and Pichia pastoris. The increased need for phosphate, the decrease of long-chain polyP level, the accumulation of short-chain polyP, and enhanced endopolyphosphatase activity in the crude membrane fraction were observed in methanol-grown cells compared with glucose-grown cells of both species. Transcriptome analysis revealed notable differences in the expression patterns of key genes encoding proteins related to polyP metabolism. In methanol-grown cells, the genes encoding endopolyphosphatases and phosphate transporters were upregulated. The changes in polyP metabolism are probably related to the peculiarities of bioenergetics of methanol-grown cells.

Canals are supramolecular complexes observed in the cell wall of Candida maltosa grown in the presence of hexadecane as a sole carbon source. Such structures were not observed in glucose-grown cells. Microscopic observations of cells stained with diaminobenzidine revealed the presence of oxidative enzymes in the canals. 4΄,6΄-diamino-2-phenylindole staining revealed that a substantial part of cellular polyphosphate was present in the cell wall of cells grown on hexadecane in condition of phosphate limitation. The content and chain length of polyphosphates were higher in hexadecane-grown cells than in glucose grown ones. The treatment of cells with yeast polyphosphatase PPX1 resulted in the decrease of the canal size. These data clearly indicated that polyphosphates are constituents of canals; they might play an important role in the canal structure and functioning.

Basidiomycetous and ascomycetous yeast species were tested for manganese tolerance. Basidiomycetous Cryptococcus humicola, Cryptococcus terricola, Cryptococcus curvatus and ascomycetous Candida maltosa, Kluyveromyces marxianus, Kuraishia capsulata, Lindnera fabianii and Sacharomyces cerevisiae were able to grow at manganese excess (2.5 mmol/L), while the growth of basidiomycetous Rhodotorula bogoriensis was completely suppressed. The lag phase duration increased and the exponential growth rate decreased at manganese excess. The increase of cell size and enlargement of vacuoles were characteristics for the cells grown at manganese excess. The alterations in inorganic polyphosphate content and cellular localization were studied. L. fabianii, K. capsulata, C. maltosa, and Cr. humicola accumulated the higher amounts of inorganic polyphosphates, while Cr. terricola and Cr. curvatus demonstrated no such accumulation. The polyphosphate content in the cell wall tested by DAPI staining increased in all species under the study; however, this effect was more pronounced in Cr. terricola and Cr. curvatus. The accumulation of Mg2+ in the cell wall under Mn2+ excess was observed in Cr. humicola, Cr. curvatus and Cr. terricola. The accumulation of polyphosphate and magnesium in the cell wall was supposed to be a factor of manganese tolerance in yeasts.

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.

The ability of Saccharomyces cerevisiae to adapt to toxic Mn(2+) concentration (4 mM) after an unusually long lag phase has been demonstrated for the first time. The mutants lacking exopolyphosphatase PPX1 did not change the adaptation time, whereas the mutants lacking exopolyphosphatase PPN1 reduced the lag period compared with the wild-type strains. The cell populations of WT and ΔPPN1 in the stationary phase at cultivation with Mn(2+) contained a substantial number of enlarged cells with a giant vacuole. The adaptation correlated with the triggering of polyphosphate metabolism: the drastic increase in the rate and chain length of acid-soluble polyphosphate. The share of this fraction, which is believed to be localized in the cytoplasm, increased to 76%. Its average chain length increased to 200 phosphate residues compared with 15 at the cultivation in the absence of manganese. DAPI-stained inclusions in the cytoplasm were accumulated in the lag phase during the cultivation with Mn(2+).

The search for new phosphate-accumulating microorganisms is of interest in connection with the problem of excess phosphate in environment. The ability of some yeast species belonging to ascomycetes and basidiomycetes for phosphate (P i) accumulation in nitrogen-deficient medium was studied. The ascomycetous Saccharomyces cerevisiae and Kuraishia capsulata and basidiomycetous Cryptococcus humicola, Cryptococcus curvatus, and Pseudozyma fusiformata were the best in P i removal. The cells of Cryptococcus humicola and S. cerevisiae took up 40% P i from the media containing P i and glucose (5 and 30 mM, respectively), and up to 80% upon addition of 5 mM MgSO4 . The cells accumulated P i mostly in the form of polyphosphate (PolyP). In the presence of Mg2+ , the content of PolyP with longer average chain length increased in both yeasts; they both had numerous inclusions fluorescing in the yellow region of the spectrum, typical of DAPI-PolyP complexes. Among the yeast species tested, Cryptococcus humicola is a new promising model organisms to study phosphorus removal from the media and biomineralization in microbial cells.

Inorganic polyphosphate (PolyP), a bioactive polymer with multiple functions, plays a key role in biomineralizaion and phosphorus homeostasis in yeasts. After phosphate starvation, the cells of Saccharomyces cerevisiae restored their pool of PolyP during the first 30 min of incubation in the media containing phosphate and carbon sources. The cells of parent strain accumulated PolyP both in glucose and ethanol-containing media. In the medium with glucose, the strain with inactivated PPX1 and PPN1 genes (encoding two major yeast polyphosphatases) accumulated 2-fold more PolyP than the parent strain. The PolyP in the mutant cells had a greater average chain length compared to the parent strain. The strain with inactivated exopolyphosphatase genes РРХ1 and PPN1 was incapable of PolyP synthesis in the medium with ethanol. The in vivo staining of cells with DAPI show that in the cells of parent strain PolyP appeared first in cytoplasm and mitochondria under cultivation in glucose-containing medium and in cytoplasm and vacuoles in the medium with ethanol. In the ΔPPX1ΔPPN1double mutant PolyP accumulated in cytoplasm and vacuoles under cultivation in glucose-contained medium.

The cells of Acetobacter xylinum decreased phosphate concentration in the medium from 5 to 2.5 or 0.3 mM during incubation in the presence of Mg(2+) and glucose, or Mg(2+) and casamino acids, respectively. The prevalence of orthophosphate or polyphosphate in the biomass of A. xylinum depends on the medium composition. Under phosphate uptake in the presence of glucose, the content of orthophosphate in the biomass changed little, while that of polyphosphate increased fourfold. At incubation with casamino acids, the content of orthophosphate increased 15 times, while that of polyphosphate increased only 2.5 times. Some part of orthophosphate in this case seems to be bound with the cell surface. The polyphosphate chain length in the cells of A. xylinim increases under phosphate uptake. This increase is more noticeable in the presence of glucose. Casamino acids can be replaced by alpha-ketoglutaric acid in combination with (NH(4))(2)SO(4), or arginine, or glutamine, the catabolism of which results in formation of NH(4) (+) and alpha-ketoglutarate.