Monovalent cation fluxes and physiological changes of Debaryomyces hansenii grown at high concentrations of KCl and NaCl (original) (raw)
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Kinetics of cation movements inDebaryomyces hansenii
Folia Microbiologica, 1998
In view of the importance of soil salinization phenomena, significant efforts have been made to understand the mechanisms underlying halotolerance developed by eukaryotic walled cells , taking yeast cells as experimental model. Most of these studies on yeast cells were done on S. cerevisiae, a moderately halotolerant yeast for which a considerable amount of information has been published.
Ionic composition and transport mechanisms in microbial
2012
Microbial desalination cell (MDC) offers a new and sustainable approach to desalinate saltwater by directly utilizing the electrical power generated by bacteria during organic matter oxidation. The successful MDC development relies on the fundamental understanding of the interactions and removal mechanisms of different ion species present in saline water or wastewater, but there is limited understanding of ion transport mechanisms in MDCs and potential membrane fouling/scaling during treatment of wastewater and saline water. In this study, we investigated the transport behavior of multiple ions in MDCs and the effects of ionic composition on system performance and membrane scaling and fouling. The results showed that the presence of sparingly soluble cations in saltwater negatively affected MDC power generation and desalination. Membrane characterization revealed that the majority of such ions precipitated on the ion exchange membrane surface and caused membrane scaling. Anions such as Br − and SO 4 2− with Na + as counter-ion did not show significant effects on system performance. Sharp pH changes were observed during MDC operation, which resulted in the inhibited MDC anode microbial activity and the accelerated formation of alkaline precipitations on both sides of the cation exchange membrane. An anode-cathode recirculation approach was proved to be effective to solve such problems and improved the desalination rate by 152% and the electron harvest rate by 98%.
Archives of Microbiology, 1989
The biomass concentration extant in potassiumlimited cultures of either KlebsielIa pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pHdependent decrease in the cells' minimum K + requirement. Significantly, this effect of pH was not evident with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH4C1 were added to the glutamate-containing medium. This suggested a functional replacement of K + by NH2, a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 A) and the ammonium ion (1.43 A). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH,C1 (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassiumlimited medium containing initially 0.5 mM K +. Qualitatively similar findings were made with cultures of K. pneumoniae; and whereas one may not conclude that NH2 can totally replace K + in the growth of these bacteria, it can clearly do so very extensively.
Ion transport and osmotic adjustment in Escherichia coli in response to ionic and non-ionic osmotica
Environmental Microbiology, 2009
Bacteria respond to osmotic stress by a substantial increase in the intracellular osmolality, adjusting their cell turgor for altered growth conditions. Using Escherichia coli as a model organism we demonstrate here that bacterial responses to hyperosmotic stress specifically depend on the nature of osmoticum used. We show that increasing acute hyperosmotic NaCl stress above~1.0 Os kg -1 causes a dose-dependent K + leak from the cell, resulting in a substantial decrease in cytosolic K + content and a concurrent accumulation of Na + in the cell. At the same time, isotonic sucrose or mannitol treatment (non-ionic osmotica) results in a gradual increase of the net K + uptake. Ion flux data are consistent with growth experiments showing that bacterial growth is impaired by NaCl at the concentration resulting in a switch from net K + uptake to efflux. Microarray experiments reveal that about 40% of upregulated genes shared no similarity in their responses to NaCl and sucrose treatment, further suggesting specificity of osmotic adjustment in E. coli to ionic and non-ionic osmotica. The observed differences are explained by the specificity of the stress-induced changes in the membrane potential of bacterial cells highlighting the importance of voltage-gated K + transporters for bacterial adaptation to hyperosmotic stress.
1996
Strain LBS3 is a novel anaerobic thermoalkaliphilic bacterium that grows optimally at pH 9.5 and 50؇C. Since a high concentration of Na ؉ ions is required for growth, we have analyzed the primary bioenergetic mechanism of energy transduction in this organism. For this purpose, a method was devised for the isolation of right-side-out membrane vesicles that are functional for the energy-dependent uptake of solutes. A strict requirement for Na ؉ was observed for the uptake of several amino acids, and in the case of L-leucine, it was concluded that amino acid uptake occurs in symport with Na ؉ ions. Further characterization of the leucine transport system revealed that its pH and temperature optima closely match the conditions that support the growth of strain LBS3. The ATPase activity associated with inside-out membrane vesicles was found to be stimulated by both Na ؉ and Li ؉ ions. These data suggest that the primary mechanism of energy transduction in the anaerobic thermoalkaliphilic strain LBS3 is dependent on sodium cycling. The implications of this finding for the mechanism of intracellular pH regulation are discussed.
Intracellular pH homeostasis plays a role in the NaCl tolerance of Debaryomyces hansenii strains
Applied Microbiology and Biotechnology, 2006
The effects of NaCl stress on cell area and intracellular pH (pH i ) of individual cells of two Debaryomyces hansenii strains were investigated. Our results show that one of the strains was more NaCl tolerant than the other, as determined by the rate of growth initiation. Whereas NaCl stress caused similar cell shrinkages (30-35%), it caused different pH i changes of the two D. hansenii strains; i.e., in the more NaCl-tolerant strain, pH i homeostasis was maintained, whereas in the less NaCltolerant strain, intracellular acidification occurred. Thus, cell shrinkage could not explain the different intracellular acidifications in the two strains. Instead, we introduce the concept of yeasts having an intracellular pK a (pK a,i ) value, since permeabilized D. hansenii cells had a very high buffer capacity at a certain pH. Our results demonstrate that the more NaCl-tolerant strain was better able to maintain its pK a,i close to its pH i homeostasis level during NaCl stress. In turn, these findings indicate that the closer a D. hansenii strain can keep its pK a,i to its pH i homeostasis level, the better it may manage NaCl stress. Furthermore, our results suggest that the NaCl-induced effects on pH i were mainly due to hyperosmotic stress and not ionic stress.
pH and monovalent cations regulate cytosolic free Ca 2+ in E. coli
Biochimica Et Biophysica Acta-biomembranes, 2008
The results here show for the first time that pH and monovalent cations can regulate cytosolic free Ca 2+ in E. coli through Ca 2+ influx and efflux, monitored using aequorin. At pH 7.5 the resting cytosolic free Ca 2+ was 0.2-0.5 µM. In the presence of external Ca 2+ (1 mM) at alkaline pH this rose to 4 µM, being reduced to 0.9 µM at acid pH. Removal of external Ca 2+ caused an immediate decrease in cytosolic free Ca 2+ at 50-100nM s − 1 . Efflux rates were the same at pH 5.5, 7.5 and 9.5. Thus, ChaA, a putative Ca 2+ /H + exchanger, appeared not to be a major Ca 2+ -efflux pathway. In the absence of added Na + , but with 1 mM external Ca 2+ , cytosolic free Ca 2+ rose to approximately 10 µM. The addition of Na + (half maximum 60 mM) largely blocked this increase and immediately stimulated Ca 2+ efflux. However, this effect was not specific, since K + also stimulated efflux. In contrast, an increase in osmotic pressure by addition of sucrose did not significantly stimulate Ca 2+ efflux. The results were consistent with H + and monovalent cations competing with Ca 2+ for a non-selective ion influx channel. Ca 2+ entry and efflux in chaA and yrbG knockouts were not significantly different from wild type, confirming that neither ChaA nor YrbG appear to play a major role in regulating cytosolic Ca 2+ in Escherichia coli. The number of Ca 2+ ions calculated to move per cell per second ranged from b 1 to 100, depending on conditions. Yet a single eukaryote Ca 2+ channel, conductance 100 pS, should conduct N 6 million ions per second. This raises fundamental questions about the nature and regulation of Ca 2+ transport in bacteria, and other small living systems such as mitochondria, requiring a new mathematical approach to describe such ion movements. The results have important significance in the adaptation of E. coli to different ionic environments such as the gut, fresh water and in sea water near sewage effluents.
Varietal differences in physiological and biochemical responses to changes in the ionic environment
Plant and Soil, 1983
Experimental assessment of differences between cultivars of crop species or ecotypes of wild species from different localities in their capacities for ion absorption and transport is made difficult by the problem of obtaining seed material of comparable ionic content. When young seedlings are used this problem is particularly acute if the seeds of the different cultivars have not been raised under identical soil conditions. Propagation of material from ecotypes under controlled conditions is one approach to the solution of this problem. Six maize cultivars have been selected for similarity of phosphate content and the capacity for phosphate absorption from 5/IM KH2PO4 has been shown to vary by threefold whereas the proportion of the accumulated phosphate that reaches the shoot differs by much less. This level of phosphate supply approached that likely to induce deficiency and when the concentration is reduced to 1 #M differences in transport capacity of up to fourfold were observed when the rate of arrival at the tip of the first leaf was continuously monitored. The rapidity with which the transport is shut off by adding l mM D(4-) mannose to the root environment also varies significantly indicating that sizeable differences in either the accumulation of mannose or the activity of phosphomannoisomerase exist in these cultivars. Ecotypes of A rmeria maritima collected from three sites, inland serpentine, inland mine dumps and coastal salt marsh were maintained as stock plants on the same peat mixture. Samples taken from these stocks were raised on a standard culture solution to provide genetically different material grown under constant conditions. The capacities for ion uptake were shown to differ very considerably and these differences were accentuated when the plants were grown in a range of concentrations of MgSO4, NaCI and MnSO4. The absorption of phosphate and its incorporation into nucleic acids were increased temporarily in the presence of 50 mM MgSO4 but the pattern of these changes was different in the three ecotypes. The absorption ofNa, CI, and Rb was measured after treatment with a range of concentrations of NaCI and the effect of treatment with MnSO4 on subsequent absorption of Mn and SO4 was also measured. The coastal plants were significantly more efficient in their absorption of these ions when treated at the lower levels of NaCI (0.5 and 10.0 mM). The short term absorption rates were not reflected in the overall accumulation of sodium over periods of 10 weeks and the coastal plants appeared to reduce the root content of sodium by transfer to the shoot and by increased active pumping to the exterior,