Role of the conidium in dimorphism of Blastomyces dermatitidis

Fine details of yeastlike cell development of Blastomyces dermatitidis from its conidium are described and illustrated by electron micrographs. When cultured in an enriched medium at 37 °C, conidia of two strains of B. dermatitidis readily underwent ultrastructural changes consistent with mycelial to yeast dimorphism. Although hyphal cells contained in the conversion cultures were observed consistently to undergo profound degenerative changes, the conidia rapidly germinated to give rise to short germ tubes which subsequently enlarged to form intermediate yeast mother cells (YMC). The wall of the germ tube arose from the innermost layer of the wall of the germinant. During the transition globoid osmiophilic inclusions of unknown origin and function were observed in vacuolated areas of the germ tube and YMC cytoplasm. Yeastlike daughter cells then budded from the intermediate YMC. Since transformation was readily accomplished under in vitro conditions favoring mycelial to yeast dimorphism, it is suggested that the conidium of B. dermatitidis represents the primary infective unit of this pathogenic fungus.     

Mannan structural complexity is decreased when Candida albicans is cultivated in blood or serum at physiological temperature

The Candida albicans cell wall provides an architecture that allows for the organism to survive environmental stress as well as interaction with host tissues. Previous work has focused on growing C. albicans on media such as Sabouraud or YPD at 30 °C. Because C. albicans normally colonizes a host, we hypothesized that cultivation on blood or serum at 37 °C would result in structural changes in cell wall mannan. C. albicans SC5314 was inoculated onto YPD, 5% blood, or 5% serum agar media three successive times at 30 °C and 37 °C, then cultivated overnight at 30 °C in YPD. The mannan was extracted and characterized using 1D and 2D ¹H NMR techniques. At 30 °C cells grown in blood and serum contain less acid-stable terminal β-(1→2)-linked d-mannose and α-(1→2)-linked d-mannose-containing side chains, while the acid-labile side chains of mannan grown in blood and serum contain fewer β-Man-(1→2)-α-Man-(1→ side chains. The decrement in acid-stable mannan side chains is greater at 37 °C than at 30 °C. Cells grown on blood at 37 °C show fewer →6)-α-Man-(1→ structural motifs in the acid-stable polymer backbone. The data indicate that C. albicans, grown on media containing host-derived components, produces less complex mannan. This is accentuated when the cells are cultured at 37 °C. This study demonstrates that the C. albicans cell wall is a dynamic and adaptive organelle, which alters its structural phenotype in response to growth in host-derived media at physiological temperature.     

Effect of temperature and temperature shifts on growth and branching of a wild type and a temperature sensitive colonial mutant (Cot 1) of Neurospora crassa

Growth of a temperature sensitive colonial mutant (cot 1) of Neurospora crassa was compared with a wild type strain. The hyphal growth unit (the ratio between mycelial length and number of branches) of the wild type was not appreciably altered by temperature and there was a direct relationship between the specific growth rate () of these mycelia and their mean hyphal extension rate (E). The specific growth rate of cot 1 increased by about the same relative amount as the wild type between 15° and 30°C. Cot 1 grew and branched normally at 15° and 25°C but at 30°C the hyphal growth unit and mean hyphal extension rate of the mutant mycelia were reduced. Thus, between 15–30°C the ratio, E/ was constant for the wild type but not for cot 1.The effect of temperature and temperature shifts on extension zone length (Z), extension zone expansion time (Z _i ) and branching of leading hyphae of mature colonies were also studies.It is suggested that branching is governed by a mechanism which regulates the linear growth rate of hyphae; the cot 1 mutation may have a direct effect on wall extension or affect linear growth rate indirectly due to an influence on the transport of precursors to the tip.     

Combined Effects of Algal (<Emphasis Type="Italic">Chlorella vulgaris</Emphasis>) Food Level and Temperature on the Demography of <Emphasis Type="Italic">Brachionus havanaensis</Emphasis> (Rotifera): a Life Table Study

We evaluated the combined effects of food (0.5 × 10⁶, 1.0 × 10⁶ and 2.0 × 10⁶ cells ml⁻¹ of Chlorella vulgaris) and temperature (15, 20 and 25 °C) on life history variables of B. havanaensis. Regardless of Chlorella density there was a steep fall in the survivorship of B. havanaensis at 25 °C. Both food level and temperature affected the fecundity of B. havanaensis. At any given food level, rotifers cultured at 15 °C showed extended but low offspring production. At 25 °C, offspring production was elevated, the duration of egg laying reduced and the fecundity was higher during the latter part of the reproductive period. The effect of food level was generally additive, at any given temperature, and higher densities of Chlorella resulted in higher offspring production. Average lifespan, life expectancy at birth and generation time were 2–3 times longer at 15 °C than at 25 °C. At 20 °C, these remained at intermediate levels. The shortest generation time (about 4 days) was observed at 25 °C. Gross and net reproductive rates and the rate of population increase (r) increased with increasing temperature and generally, at any given temperature, higher algal food levels contributed to higher values in these variables. The r varied from 0.11 to 0.66. The survival patterns and lower rates of reproduction at 15 °C suggest that the winter temperatures (10–15 °C) prevailing in many waterbodies in Mexico City allow this species to sustain throughout the year under natural conditions.     

Studies on the growth and encystment ofPolytomella agilis

Summary Changes in cell population density, cell protein and cell carbohydrate levels of the flagellatePolytomella agilis during growth in batch cultures on a complex medium at 25° C, 18° C and 9° C were examined. At 25° C, cell protein and carbohydrate levels fell markedly during exponential population growth. At 18° C, cell protein values remained fairly constant, while cell carbohydrate increased. During growth at 9° C, both cell protein and carbohydrate increased. Changes in these cellular parameters were related to marked differences in the rates of population growth at these temperatures. The cellular locus of changes observed at 25° C was examined by centrifugal fractionation of disrupted cells on density gradients.Encystment was studied in cultures grown at 25° C. The maximum number of cysts produced was 5–10 per cent of the peak population density; the rate and degree of encystment were not increased by growth on conditioned medium or starvation. Cysts isolated from mixed populations by a centrifugal procedure remained viable, even after storage at —5° C for several weeks. The soluble proteins of separately disrupted motile and encysted forms ofP. agilis were examined and compared by disc electrophoresis.This investigation was supported by U.S.P.H.S. Grant AI-07926-02.     

Ultrastructural and protein changes in cell suspension cultures of peach associated with low temperature-induced cold acclimation and abscisic acid treatment

Cell suspension cultures were initiated from callus derived from xylem tissues of peach [Prunus persica (L.) Batsch]. Cold acclimation was induced (LT₅₀ of-13°C) in cell suspensions at 3°C in the dark for 10 days. Freezing tolerance returned to the level of nonacclimated cells (LT₅₀ of –4.5°C) when cold-acclimated cells were transferred to 24°C (in dark) for 3 days. Addition of 75 M abscisic acid (ABA) to the growth medium failed to induce cold acclimation after cells were cultured for 5 days at 24°C. Microvacuolation, cytoplasmic augmentation and disappearance of starch grains were observed in cells that were cold-acclimated by exposure to low temperature. Similar ultrastructural alterations were not observed in ABA-treated cells. Several qualitative and quantitative changes in proteins were noted during both cold acclimation and ABA treatment. Both the ultrastructural and protein changes observed during cold acclimation were reversed during deacclimation. The relationship of these changes to cold acclimation in peach cell-cultures is discussed.Abbreviations ABA abscisic acid - 2,4-d 2,4-dichlorophenoxyacetic acid - IBA indole-3-butyric acid - Ms Murashige & Skoog - PMSF phenylmethylsulfonyl fluoride - LT₅₀ or Freezing Tolerance temperature that resulted in 50% decrease in TTC reduction - TTC 2,3,5-triphenyltetrazolium chloride     

Growth and adaptation to phototrophic conditions of Rhodospirillum rubrum and Rhodopseudomonas sphaeroides at different temperatures

The influence of temperature on yields of cell protein and bacteriochlorophyll as well as on the rates of growth and bacteriochlorophyll synthesis was studied with Rhodospirillum rubrum and Rhodopseudomonas sphaeroides. Under chemotrophic conditions net cell-protein production increased in cultures of both species along with temperature from 14°C up to the optimum at 33°C. Under phototrophic conditions cell-protein yields were largely constant within the range from 21°C to 33°C. At temperatures below 21°C and above 33°C yields decreased. These results are interpreted in terms of coupling between energy yielding or redox equivalent providing metabolisms and cell biosynthesis. Upon adaptation from chemotrophic to phototrophic conditions a direct relationship between temperature increase and bacteriochlorophyll level was observed. Arrhenius plots of both, specific growth rates and rates of bacteriochlorophyll synthesis, revealed discontinuities at about 20°C. Temperature coefficients either above or below those discontinuities were similar in both species. In R. rubrum temperature coefficients of the synthesis of total bacteriochlorophyll were also representative of the synthesis of photochemical reaction center and light harvesting bacteriochlorophylls. But in R. sphaeroides significant differences were observed between temperature coefficients of the syntheses of bacteriochlorophylls of the costantly composed reaction centerlight harvesting complex on one hand and of both, total and the quantitatively variable light harvesting bacteriochlorophylls on the other. The results are interpreted in light of hypotheses on the regulation (a) of cellular bacteriochlorophyll levels as well as (b) of the ratio of functionally different bacteriochlorophylls in the photosynthetic apparatus.Abbreviation Bchl bacteriochlorophyll     

Gonadal sex differentiation in Alligator mississippiensis,a species with temperature-dependent sex determination

Temperature of egg incubation determines sex in Alligator mississippiensis hatchlings. To define the timing and morphology of sexual differentiation, alligator gonads were examined histologically and ultrastructurally throughout embryogenesis. At the male-producing temperature (33° C), the onset of testis differentiation occurred in most embryos during developmental stages 21–22, when a number of somatic cells in the medulla of the gonad became enlarged, forming presumptive Sertoli cells. Some enlarged somatic cells were also observed at the female-producing temperature (30° C) during gonadogenesis, but they were less widespread than at 33° C. Ovarian differentiation at 30° C began slighlty later, during stage 22–23, and was characterised by proliferation of germs cells in the cortex of the gonad. Testis formation in alligators may depend upon presumptive Sertoli cells differentiating prior to a critical event in embryogenesis, such as germ cell proliferation and meiosis. If follows that ovary formation occurs if this requirement is not met, as at lower incubation temperatures.     

Effect of temperature and oxygen on cell growth and recombinant protein production in insect cell cultures

The effect of temperature and O₂ saturation on the production of recombinant proteins -galactosidase and human glucocerebrosidase by Spodoptera frugiperda cells (Sf9) infected with recombinant Autographa californica nuclear polyhedrosis virus was investigated. The rates of cell growth, glucose consumption, O₂ consumption and product expression were measured at temperatures between 22° C and 35° C. The results indicated that possible O₂ limitation may be alleviated without compromising the maximum cell yield by lowering the incubation temperature from 27° C to 25° C. The expression level of the recombinant proteins at 27° C was similar to that obtained at 22° C and 25° C; lower protein yields were obtained at 30° C. An increase in temperature from 22° C to 27° C led to earlier production of the proteins and to an increase in the proportion of the product released outside the cells. Correspondence to: J. Shiloach     

Resolution of pheromone pulses in receptor cells of Antheraea polyphemus at different temperatures

The ability of pheromone receptor cells of male Antheraea polyphemus (Saturniidae) to resolve stimulus pulses was determined at different temperatures (8°, 18°, 28°C). The cells were stimulated by repeated 20-ms puffs of the pheromone components (E, Z)-6, 11-hexadecadienyl acetate and (E, Z)-6,11-hexadecadienal. At higher temperatures, higher frequencies of stimulus pulses were resolved by the nerve-impulse response: about 1.25 pulses per second at 8°C, 2.5 pulses/s at 18°C and 5 pulses/s at 28°C. The decreased ability of receptor cells to resolve stimulus pulses at low temperatures may reduce the male moth's chance of reaching the pheromone source. The peak nerve-impulse frequency increased whereas the duration of nerve-impulse responses to single stimulus pulses decreased at higher temperatures. At a given temperature and stimulus intensity the peak nerveimpulse frequency decreased with shorter intervals between the stimulus pulses, but the duration of the responses remained almost constant. The time needed for recovery from adaptation caused by a single stimulus pulse was longer at lower temperatures. The aldehyde receptor cell recovered more quickly than the acetate cell. At low stimulus concentration, the resolution ability of the acetate cell was strongly decreased, whereas in the aldehyde cell it was only slightly impaired.     

Influence of Temperature and Methyl Jasmonate on Scenedesmus Incrassulatus

The effect of the methyl ester of jasmonic acid (MeJA) in 10 M concentration was studied on the development of the bacterial contaminants and on the content of some metabolites in Scenedesmus incrassulatus cultivated at temperatures 15, 20, 25, 30, and 36 °C. The number of bacteria on algae cells increased with the rise in temperature. Application of MeJA into nutrient medium inhibited the development of bacterial pathogens more than 3 times at 20 °C, 2.3 times at 30 °C, and 2.6 times at 36 °C without changing the species composition. MeJA caused an increase of the protein content in algae cells. The contents of palmitic and linoleic acids increased with the rise of temperature from 15 to 36 °C. At the same time the contents of linolenic and oleic acid decreased. At low temperatures, cultivation with MeJA induced more significant changes in the composition of C18 acids while at high temperature the changes were more pronounced in C16 acids. Treatment with MeJA decreased the activity of glutamate dehydrogenase at optimal and suboptimal temperatures and increased it at superoptimal temperature. Hence MeJA jasmonate had a positive effect on the tolerance of S. incrassulatus to stress temperatures, which was also demonstrated by better growth.     

Changes in leaf ultrastructure and carbohydrates inArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation

Summary We studied cell ultrastructure and carbohydrate levels in the leaf tissue ofArabidopsis thaliana L. (Heyn) cv. Columbia during rapid cold acclimation. Freezing tolerance of the leaves from 26 day old plants was determined after 48 h and 10 days at 4°C. Acclimation treatment of 48 h decreased the lethal freezing temperature from –5.7°C to –9.4°C. Freezing tolerance was not altered further by acclimation at 4 °C for 10 days. Ultrastructural changes in the parenchyma cells were evident after 6 to 24 h of cold acclimation. The plasma membrane showed signs of extensive turnover. Evidence of membrane invaginations and sequestering of membrane material was observed. In addition, numerous microvesicles, paramural bodies, and fragments of endoplasmic reticulum were noticed in the vicinity of plasma membrane. Modifications in the structure of cell membranes were evident after 5 days of exposure to low temperature. Small, darkly stained globules were seen on the plasma membrane, tonoplast, chloroplast envelope membrane, mitochondrion outer membrane, dictyosome cisternae membrane, and microvesicle membrane. As far as we are aware, this type of membrane modification has not been described previously in plant cells exposed to low temperature. We propose to call these structures membraglobuli. Acclimation treatment also increased the concentrations of soluble sugars and starch. These observations suggest that cold acclimation inA. thaliana induces changes in both plasma membrane properties and carbohydrate composition.     

Lipid polymers accumulate in the epidermis and mestome sheath cell walls during low temperature development of winter rye leaves

Summary Winter rye (Secale cereale L cv. Puma) was grown at 20 °C and at 5 °C and the development of epidermal and mestome sheath cells of leaves from plants grown at both temperatures was compared by electron microscopy. At 5 °C, the cells became densely packed with cytoplasm and small vacuoles after 41 days of growth. By day 56 at 5 °C, epidermal and mestome sheath cells were small in diameter and multivacuolate with asymmetrically thickened walls. By day 76 at 5 °C, a new developmental stage had been reached in epidermal and mestome sheath cells. The cells were larger in diameter although the thickened cell walls and multivacuolate cytoplasm were still present. As epidermal and mestome sheath cell walls thickened during low temperature growth of winter rye, an increase in cuticle thickness and the deposition of a lamellar layer could be observed in epidermal and mestome sheath cells, respectively. The lipid-derived polymers from the leaves of rye plants grown at 20 °C were shown by reductive depolymerization and GC-MS analysis to be comprised of 18-hydroxy-9, 10-epoxyoctadecanoic acid (47%) and dihydroxyhexa-decanoic acid (29%). The leaves of plants grown at 5 °C had two to four times as much lipid-derived polymeric material as those grown at 20 °C and the proportion of the major monomer, 18-hydroxy-9,10-epoxyoctadecanoic acid, increased to 73% of the polymeric material. Physical isolation of both epidermal tissue and vascular bundles followed by GC-MS analysis of the monomeric components released by reduction of the respective lipid polymers showed that 18-hydroxy-9,10 epoxyoctadecanoic acid was the major monomer in the polymer of both the epidermis and the mestome sheaths. The presence of this epoxide monomer in both the cuticles and mestome sheath cell walls of rye leaves was confirmed and visualized by using an epoxide-specific staining reaction.     

Studies of the functional activity of mitochondria and cell ultrastructure of the coleoptile in wheat,Agropyron and their hybrids (incomplete amphidiploids) during decreasing temperature

Summary The structure of the mitochondria and endoplasmic reticulum in the coleoptile of plants (Triticum aestivum var. Lutescens 329, Agropyron glaucum, Triticum × Agropyron 56-chromosome hybrids, incomplete amphidiploids, TAH, containing 42 wheat chromosomes and 14 chromosomes of genomes D or X of Agropyron), which differ in winterhardiness, was studied after exposure to 0 ° and -4 °C for periods varying from 10 min to 4 days. The functional activity of mitochondria isolated from 3 day old seedlings was also investigated in these cereals. The cells of Triticum and Agropyron seedlings grown at 23 °C were shown to differ in mitochondrial structure. In the cells of TAH both kinds of mitochondria were found.On day 4 of exposure to -4 °C, the mitochondria of Agropyron cells were not changed; the endoplasmic reticulum formed complex closed cavities. Under similar conditions most wheat mitochondria were destroyed and in the rest no cristae were observed.Morphometric analysis indicated that the volume of such mitochondria increases by two times, while the surface area of the internal membranes and cristae decreases by 1.54 times. In such cells, the endoplasmic reticulum is represented only by membranes of the smooth type. The structure of the mitochondria and endoplasmic reticulum in the seedling cells of TAH 829, which is more like Agropyron in winterhardiness, is similar to that of Agropyron cells; in hybrid 822 (more like wheat containing the D genome), changes arise resembling those observed in wheat. The existence of different types of mitochondria in seedling cells of TAH is especially distinct at low temperatures.The mitochondria of the cereals studied differ in biochemical activity after low temperature treatment (0 ° and — 4 °C). Phosphorylative and oxidative activity of mitochondria of the winterhardy forms (Agropyron glaucum, TAH 829) decreases just after the beginning of low temperature treatment. At the same time, the morphology of the mitochondria undergoes reversible changes. The mitochondria of cold-susceptible forms of wintering plants (Triticum aestivum, TAH 822) do not conform to this pattern. Under long-term low temperature treatment they display irreversibly damaged mitochondria. It is suggested that the winterhardy forms have high adaptability connected with a rapid protective response of the cell mitochondria and endoplasmic reticulum. This adaptability is regulated by nuclear genes: TAH have different mitochondria in the coleoptile cells; if genome X of Agropyron is present, which TAH derives from the male parent, the related mitochondria become more resistant to low temperature treatment.     

Genome-wide expression analysis of yeast response during exposure to 4°C

Adaptation to temperature fluctuation is essential for the survival of all living organisms. Although extensive research has been done on heat and cold shock responses, there have been no reports on global responses to cold shock below 10°C or near-freezing. We examined the genome-wide expression in Saccharomyces cerevisiae, following exposure to 4°C. Hierarchical cluster analysis showed that the gene expression profile following 4°C exposure from 6 to 48 h was different from that at continuous 4°C culture. Under 4°C exposure, the genes involved in trehalose and glycogen synthesis were induced, suggesting that biosynthesis and accumulation of those reserve carbohydrates might be necessary for cold tolerance and energy preservation. The observed increased expression of phospholipids, mannoproteins, and cold shock proteins (e.g., TIP1) is consistent with membrane maintenance and increased permeability of the cell wall at 4°C. The induction of heat shock proteins and glutathione at 4°C may be required for revitalization of enzyme activity, and for detoxification of active oxygen species, respectively. The genes with these functions may provide the ability of cold tolerance and adaptation to yeast cells.     

Response of antennal cold receptors of the catopid beetles,Speophyes lucidulus Delar. andCholera angustata Fab. to very slowly changing temperature

Summary The antennal cold cells in larval black-hair sensilla of the cave beetle,Speophyes lucidulus Delar., clearly respond to rates of temperature change 5 to 10 times lower than any tested on insect cold cells so far: often below 0.0005° C/s or 2° C/h. At a given ambient temperature between 11° C and 15° C, cold-cell impulse frequency was higher when temperature was falling at these rates than when it was rising at them in every one of the twelve cells examined. The mean differential sensitivity to the rate of change was -3340±1071 (imp/s)/(° C/s), in each case two to 5 times greater (sign ignored) than in any cold cell observed previously (Loftus 1969; Corbière-Tichané and Loftus 1983). The differential sensitivity to ambient temperature,-6.8 (imp/s)/° C, was statistically indistinguishable, on the other hand, from the earlier values forSpeophyes.Antennal cold cells of six first-stage larvae of another Catopid beetle,Choleva angustata Fab., displayed very similar responses to the same stimuli. Its mean differential sensitivities were -8.1+3.9 (imp/s)/° C to ambient temperature and-3790+2190 (imp/s)/(° C/s) to the rate of temperature change. UnlikeSpeophyes this beetle spends only part of its life cycle in caves.Abbreviations dT/dt rate of temperature change in °C/s - F impulse frequency in impulses/s (imp/s) - T temperature in ° C To Sylvie Deleurance, a helpful friend who dedicated much of her life to the study of cave insects     

Microspore development inBrassica napus and the effect of high temperature on division in vivo and in vitro

Summary Brassica napus cv. Topas microspores isolated and cultured near the first pollen mitosis and subjected to a heat treatment develop into haploid embryos at a frequency of about 20%. In order to obtain a greater understanding of the induction process and embryogenesis, transmission electron microscopy was used to study the development of pollen from the mid-uninucleate to the bicellular microspore stage. The effect of 24 h of high temperature (32.5 °C) on microspore development was examined by heat treating microspore cultures or entire plants. Mid-uninucleate microspores contained small vacuoles. Late-uninucleate vacuolate microspores contained a large vacuole. The large vacuole of the vacuolate stage was fragmented into numerous small vacuoles in the late-uninucleate stage. The late-uninucleate stage contained an increased number of ribosomes, a pollen coat covering the exine and a laterally positioned nucleus. Prior to the first pollen mitosis the nucleus of the lateuninucleate microspore appeared to be appressed to the plasma membrane; numerous perinuclear microtubules were observed. Microspores developing into pollen divided asymmetrically to form a large vegetative cell with amyloplasts and a small generative cell without plastids. The cells were separated by a lens-shaped cell wall which later diminished. At the late-bicellular stage the generative cell was observed within the vegetative cell. Starch and lipid reserves were present in the vegetative cell and the rough endoplasmic reticulum and Golgi were abundant. The microspore isolation procedure removed the pollen coat, but did not redistribute or alter the morphology of the organelles. Microspores cultured at 25 °C for 24 h resembled late-bicellular microspores except more starch and a thicker intine were present. A more equal division of microspores occurred during the 24 h heat treatment (32.5 °C) of the entire plant or of cultures. A planar wall separated the cells of the bicellular microspores. Both daughter cells contained plastids and the nuclei were of similar size. Cultured embryogenie microspores contained electron-dense deposits at the plasma membrane/cell wall interface, vesicle-like structures in the cell walls and organelle-free regions in the cytoplasm. The results are related to embryogenesis and a possible mechanism of induction is discussed.Abbreviations B binucleate - LU late uninucleate - LUV late uninucleate vacuolate - M mitotic - MU mid-uninucleate - RER rough endoplasmic reticulum - TEM transmission electron micrograph     

Low Temperature Stimulates Cell Enlargement and Intracellular Calcification of Coccolithophorids

Temperature effect on growth, cell size, calcium uptake activity, coccolith production was studied in coccolith-producing haptophytes, Emiliania huxleyi (Lohmann) Hay & Mohler (strain EH2) and Gephyrocapsa oceanica Kamptner (strain GO1) (Coccolithophorales, Prymnesiophyceae). E. huxleyi grew at a wider temperature range (10°–25°C), while G. oceanica growth was limited to warmer temperatures (20°–25°C). Cell size was inversely correlated with temperature. At low temperature, the enlargement of chloroplasts and cells and the stimulation of coccolith production were morphologically confirmed under fluorescent and polarization microscopes, respectively. ⁴⁵ Ca uptake by E. huxleyi at 10°C was greatly increased after a 5-day lag and exceeded that at 20°C. These results clearly showed that low temperature suppressed coccolithophorid growth but induced cell enlargement and as stimulated the intracellular calcification that produces coccoliths.     

Influence of temperature on the properties of the xylanolytic enzymes of the thermotolerant fungus<Emphasis Type="Italic"> Aspergillus phoenicis</Emphasis>

This study reports on the effects of growth temperature on the secretion and some properties of the xylanase and -xylosidase activities produced by a thermotolerant Aspergillus phoenicis. Marked differences were observed when the organism was grown on xylan-supplemented medium at 25 °C or 42 °C. Production of xylanolytic enzymes reached maximum levels after 72 h of growth at 42 °C; and levels were three- to five-fold higher than at 25 °C. Secretion of xylanase and -xylosidase was also strongly stimulated at the higher temperature. The optimal temperature was 85 °C for extracellular and 90 °C for intracellular -xylosidase activity, independent of the growth temperature. The optimum temperature for extracellular xylanase increased from 50 °C to 55 °C when the fungus was cultivated at 42 °C. At the higher temperature, the xylanolytic enzymes produced by A. phoenicis showed increased thermostability, with changes in the profiles of pH optima. The chromatographic profiles were distinct when samples obtained from cultures grown at different temperatures were eluted from DEAE–cellulose and Biogel P-60 columns.     

The effects of temperature on the fatty acid and phospholipid composition of four obligately psychrophilicVibrio Spp.

The free fatty acid and phospholipid composition of 4 psychrophilic marineVibrio spp. have been determined in chemostat culture with glucose as the limiting substrate over a temperature range 0–20°C. All the isolates show maximum glucose and lactose uptake at 0°C and this correlates with maximum cell yield. None of the isolates contain fatty acids with a chain length exceeding 17 carbon atoms.Vibrio AF-1 andVibrio AM-1 respond to decreased growth temperatures by synthesizing increased proportions of unsaturated fatty acids (C15:1, C16:1 and C17:1) whereas inVibrio BM-2 the fatty acids undergo chain length shortening. The fourth isolate (Vibrio BM-4) contains high levels (60%) of hexadecenoic acid at all growth temperatures and the fatty acid composition changes little with decreasing temperature. The principal phospholipid components of the four psychrophilic vibrios were phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Lyso-phosphatidylethanolamine and 2 unknown phospholipids were additionally found inVibrio AF-1. The most profound effect of temperature on the phospholipid composition of these organisms was the marked increase in the total quantities synthesized at 0°C. At 15°C phosphatidylglycerol accumulated in the isolates as diphosphatidylglycerol levels decreased. Additionally inVibrio BM-2 andVibro BM-4 phosphatidylserine accumulates as phosphatidylethanolamine biosynthesis was similarly impaired. The observed changes in fatty acid and phospholipid composition in these organisms at 0°C may explain how solute transport is maintained at low temperature.Abbreviations PS Phosphatidylserine - PE phosphatidylethanolamine - PG phosphatidylglycerol - DPG diphosphatidylglycerol - lyso PE lysophosphatidylethanolamine