Margaret Ginzburg

Adaptation to extreme environments: macromolecular dynamics in bacteria compared in vivo by neutron scattering

Mean macromolecular dynamics was quantified in vivo by neutron scattering in psychrophile, mesophile, thermophile and hyperthermophile bacteria. Root mean square atomic fluctuation amplitudes determining macromolecular flexibility were found to be similar for each organism at its physiological temperature (∼1 Å in the 0.1 ns timescale). Effective force constants determining the mean macromolecular resilience were found to increase with physiological temperature from 0.2 N/m for the psychrophiles, which grow at 4°C, to 0.6 N/m for the hyperthermophiles (85°C), indicating that the increase in stabilization free energy is dominated by enthalpic rather than entropic terms. Larger resilience allows macromolecular stability at high temperatures, while maintaining flexibility within acceptable limits for biological activity.

Dunaliella: a green alga adapted to salt

Publisher Summary The organism responsible for the red color was described by Teodoresco and is now named Dunafieffa safina (Dunal). It is a unicellular, photosynthetic green alga which has been placed in the division, Chlorophyta. It has two equal flagella, one cup-shaped chloroplast, an anterior nucleus, an eye-spot and a pyrenoid surrounded by starch grains at the posterior end of the cell. There is no rigid cell wall. The specific characteristics of the genus are its morphology and physiology. The cell morphology is Chlamydomonad-like. Physiologically, the genus is distinguished by the ability to grow in media with high concentrations of salt. Six freshwater species of Dunafieffa have been described; all appear to be extremely rare and their inclusion within the genus is uncertain. This chapter summarizes and analyzes the often conflicting data on Dunafielfa gathered during the past 30 years, compares and contrasts Dunafieffa with other green algae, and furthers the understanding of the adaptation of Dunaliella to high salt concentrations.

Ion metabolism in aHalobacterium : II. Ion concentrations in cells at different levels of metabolism.

SummaryThe changes in concentration of K+, Na+ and Cl− are given in growing cultures of aHalobacterium species subjected to cold, lack of O2 or starvation. In growing cells, the ion concentration ratios across the cell membrane were 1,000∶1 (inside:outside) for K+ and 1∶2 for Na+. In bacteria with a low rate of endogenous metabolism induced by 24-hr starvation, the ratios were 500∶1 for K+ and 1∶4 for Na+. O2 and a substrate were required for K+ uptake in growing bacteria, but not for the maintenance of K+ and Na+ gradients in starving bacteria. The exchange of K+, Na+ and Li+ across the cell membrane of starving bacteria was found to have a time constant for 50% completion of the process of 20 to 30 sec. The exchange of cell Cl− with NO3− was a twostage process with time constants of approximately 2 min and 2–1/2 hr. The results are explained in terms of the binding of most of the cell K+ which brings about the distribution of Na+ and Cl− according to the Gibbs-Donnan equilibrium; the role of metabolism is to induce changes in the mean ion-activity coefficients.

Neutron scattering reveals extremely slow cell water in a Dead Sea organism

Intracellular water dynamics in Haloarcula marismortui, an extremely halophilic organism originally isolated from the Dead Sea, was studied by neutron scattering. The water in centrifuged cell pellets was examined by means of two spectrometers, IN6 and IN16, sensitive to motions with time scales of 10 ps and 1 ns, respectively. From IN6 data, a translational diffusion constant of 1.3 × 10−5 cm2 s−1 was determined at 285 K. This value is close to that found previously for other cells and close to that for bulk water, as well as that of the water in the 3.5 M NaCl solution bathing the cells. A very slow water component was discovered from the IN16 data. At 285 K the water-protons of this component displays a residence time of 411 ps (compared with a few ps in bulk water). At 300 K, the residence time dropped to 243 ps and was associated with a translational diffusion of 9.3 × 10−8 cm2 s−1, or 250 times lower than that of bulk water. This slow water accounts for ≈76% of cell water in H. marismortui. No such water was found in Escherichia coli measured on BSS, a neutron spectrometer with properties similar to those of IN16. It is hypothesized that the slow mobility of a large part of H. marismortui cell water indicates a specific water structure responsible for the large amounts of K+ bound within these extremophile cells.

The unusual membrane permeability of two halophilic unicellular organisms

Abstract 1. 1. The permeability of a Halobacterium species and Dunaliella parva to several radioactive substances has been measured. 2. 2. The method used was to centrifuge a cell suspension, within which was dissolved the given radioactive substance, and measure the radioactivity of the resultant cell pellet and supernatant. The volume of radioactive substance within the cell pellet was then calculated. 3. 3. Both organisms were found to be impermeable to [ 14 C]dextran (mol. wt. 80 000). 4. 4. Results indicated that the Halobacterium cell was freely permeable to [ 14 C]-sucrose, [ 14 C]inulin, [ 14 C]starch, and even [ 14 C]polyvinylpyrollidone (mol. Wt. 30 000–40 000). 5. 5. A region of the D. parva cell was permeable to [ 14 C]surcose and to [ 14 C]inulin. 6. 6. It is argued that the results indicate the existence of large pores in the cell membranes of these two organisms.

Lipid composition of halotolerant algae, Dunaliella parva lerche and Dunaliella tertiolecta

Abstract The lipids of two halotolerant algae, Dunaliella parva Lerche and Dunaliella tertiolecta , contained predominantly the glycolipids monogalactosyldiacylglycerol (21.4 and 22.2 mol% for D. parva and D. tertiolecta , respectively), digalactosyldiacylglycerol (11.4 and 20.5 mol%), sulfoquinovosyldiacylglycerol (6.5 and 9.5 mol%) and two minor unidentified glycolipids. Phosphatidylcholine (8.8 and 4.4 mol%), phosphatidylglycerol (5.5 and 7.7 mol%) and phosphatidylinositol (1.7 and 2.5 mol%) were present in both algae, but phosphatidylethanolamine (1.9 mol%) and phosphatidic acid (1.7 mol%) were detected in only D. tertiolecta . Diacylglycerol-O-N,N,N-trimethylhomoserine was a large component in both algae (14.2 and 7.5 mol%). The major fatty acids present were linolenic, palmitic, linoleic, oleic and an unidentified acid, probably a polyunsaturated 16-carbon acid. Fatty acid analyses of individual lipids revealed several striking features that were characteristic of the lipids in both algae. In addition, both algae had characteristically high total lipid contents, in the range 20–25% on a cell protein basis.

Interrelationships of light, temperature, sodium chloride and carbon source in growth of halotolerant and halophilic strains of Dunaliella

The growth rate of several Dunaliella strains was measured as a function of several environmental parameters. The strains tested fell into two groups, the halotolerant capable of growing at 0·5 m NaCl and above, and the halophilic which cannot grow in media containing less than 2 m NaCl. It proved to be difficult to find optima for the different parameters tested because of their integrated effects within the plant cell; for instance the temperature optimum was higher at high light intensity than at lower intensities. Similarly, higher concentrations of NaCl were tolerated when the light intensity was high and carbon plentiful.

Studies of the comparative physiology of the genus Dunaliella (Chlorophyta, Volvocales). I: Response of growth to NaCl concentration

Growth curves, yields and doubling-times of six Dunaliella isolates were measured at 26 and 36°C in batch-type cultures growing at NaCl concentrations from 0·5 to 4 m. Cultures had been pre-adapted to temperature and NaCl concentration and were inoculated from cultures that were themselves in the logarithmic phase of growth. Even so, in many cases the initial growth rate was slow. The doubling-time varied in one of three ways; either it increased with outside NaCl concentration, or it remained constant, or (most often) it had a minimum value at some intermediate NaCl concentration and rose at both extremes.

Dielectric properties of the halophilic bacteria Halobacterium halobium and H. marismortui with reference to the conductivities and permittivities of the cytoplasmic membrane and intracellular phases

Abstract Dielectric measurements were performed over the frequency range 1–200 MHz on suspensions of two halophilic bacteria, Halobacterium halobium and Halobacterium marismortui . Two dielectric dispersions were observed, termed P (or β) for low frequencies and Q for higher frequencies. The dispersions were analysed according to the theory of interfacial polarization for triphasic systems. Values of membrane capacitance and conductance, and intracellular conductivity and permittivity were derived by use of the theoretical equations presented. Both species exhibited a high membrane capacitance. Results showed that H. halobium has an insulating membrane and behaves as a non-conducting particle, whereas H. marismortui (obtained from the Dead Sea) exhibits an unusually high membrane conductivity. Measurements of internal conductivity for both species point to low mobilities for the intracellular ions and internal permittivities of around 300.

Regulation of cell volume and ion concentrations in aHalobacterium

SummaryChanges in cell volume and ion content of aHalobacterium species are described in terms of the NaCl concentration (0.5–3.5m) and pH (4–8) of the suspending medium. Cell volume, per unit content of protein of bacteria in stationary phase cultures, rose as the [NaCl] of the growth medium was increased. Logarithmic-phase bacteria shrank as the pH fell from 7 to 5.5. These changes are characteristic of bacteria with a moderate or rapid rate of O2 consumption. Starving (i.e. nonmetabolizing) bacteria, on the other hand, did not change in size within the above ranges of [NaCl] and pH. At lower values, however, such bacteria swelled and eventually lysed. Effects of low pH on cell ions are compared in metabolizing and starving bacteria, and it is shown that changes in the state of the cell K are correlated with movements of cell Na. It appears that the cell K is used to maintain cell [Na] below the NaCl concentration of the medium. The results are explained in terms of a model involving interactions between polyelectrolytes, salts and water in the concentrated cytoplasm of these halophilic organisms.