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At least 127 records · Page 7Linked to original sources
PubMed1998

Enhanced Heavy Metal Tolerance in Two Strains of Photosynthetic Euglena gracilis by Preexposure to Mercury or Cadmium

The effects of different concentrations of Hg, Cd, and Pb on cell growth, oxygen consumption, and production and contents of chlorophyll a and b of Z and B strains of Euglena gracilis was studied. Cell uptake of Cd and Pb was also determined. A greater cell density reached in the presence of Cd2+ correlated with a lower metal uptake capacity in B-strain cells. Cells of Z strain, preexposed to low concentrations of either Hg2+ (1.5 μM) or Cd2+ (50 μM) for several generations showed improved heavy metal tolerance (greater cell density and viability) together with similar metal uptake capacity. Because Cd2+ preadaptation but not Hg2+ pretreatment induced a significant increase in the content of acid-soluble thiols, the data suggest the existence of different mechanisms of heavy metal detoxification in Euglena. The fact that Z-strain cells showed a greater Cd2+ uptake under all the conditions assayed suggests that Z strain would be more suitable for bioremediation of polluted waters.

Journal Article↗
PubMed2005

Decolorization of anthraquinone dye by Shewanella decolorationis S12.

A new species of genus Shewanella, Shewanella decolorationis S12, from activated sludge of a textile-printing wastewater treatment plant, can decolorize Reactive Brilliant Blue K-GR, one kind of anthraquinone dye, with flocculation first. Although S. decolorationis displayed good growth in an aerobic condition, color removal was the best in an anaerobic condition. For color removal, the most suitable pH values and temperatures were pH 6.0-8.0 and 30-37 degrees C under anaerobic culture. More than 99% of Reactive Brilliant Blue K-GR was removed in color within 15 h at a dye concentration of 50 mg/l. Lactate was the suitable carbon source for the dye decolorization. A metal compound, HgCl(2), had the inhibitory effect on decolorization of Reactive Brilliant Blue K-GR, but a nearly complete decolorization also could be observed at a HgCl(2) concentration of 10 mg/l. The enzyme activities, which mediate the tested dye decolorization, were not significantly affected by preadaptation of the bacterium to the dye.

Anthraquinones↗
PubMed2007

Fe(III)-enhanced Azo Reduction by Shewanella decolorationis S12.

Shewanella decolorationis S12 is capable of high rates of azo dye decolorization and dissimilatory Fe(III) reduction. Under anaerobic conditions, when Fe(III) and azo dye were copresent in S12 cultures, dissimilatory Fe(III) reduction and azo dye biodecolorization occurred simultaneously. Furthermore, the dye decolorization was enhanced by the presence of Fe(III). When 1 mM Fe(III) was added, the methyl red decolorizing efficiency was 72.1% after cultivation for 3 h, whereas the decolorizing efficiency was only 60.5% in Fe(III)-free medium. The decolorizing efficiencies increased as the concentration of Fe(III) was increased from 0 to 6 mM. Enzyme activities, which mediate the dye decolorization and Fe(III) reduction, were not affected by preadaption of cells to Fe(III) and azo dye nor by the addition of chloramphenicol. Both the Fe(III) reductase and the azo reductase were membrane associated. The respiratory electron transport chain inhibitors metyrapone, dicumarol, and stigmatellin showed significantly different effects on Fe(III) reduction than on azo dye decolorization.

Aerobiosis↗
PubMed2003

Investigating a new cryopreservation protocol for yams ( Dioscorea spp.).

Experiments were initiated to develop protocols for four species of Dioscorea, namely D. bulbifera L., D. oppositifolia L., D. alata L. and D. cayenensis Lam., and to assess the effects of various factors on the survival and regrowth of explants after rewarming. The treatments consisted of three different methods-vitrification, droplet and a modified droplet method-as well as the following variables-cryoprotective solution, sucrose concentration in the preadaptation medium and cold acclimation. While most of the protocols resulted in low to zero survival and regrowth rates, maximum survival rates of 100% and 75% were obtained for D. oppositifolia L. and D. cayenensis Lam., respectively, using two different protocols of the modified droplet method. A higher average survival rate was obtained using the droplet and modified droplet techniques than for the original vitrification methods. When the average of all the experiments was taken, more than one-half (52%) of the surviving explants developed further within 1 month with the modified droplet method compared to zero regrowth with the two other methods. The optimum protocol for cryopreservation is specific for each genotype.

Cryopreservation↗
PubMed2001

Protein catabolism in suckling and fasting northern elephant seal pups (Mirounga anglstirostris).

Nursing elephant seal pups are hypothesized to be preadapted to the postweaning fast, yet no comparison of lipid or protein use for meeting metabolic costs has been made between these contrasting nutritional periods. To address this, protein catabolism was estimated in five elephant seal pups from measurements of urea turnover made twice during nursing and twice during the postweaning fast. Changes in body composition were measured in ten separate weaned pups via tritiated water dilution and matched to fasting urea turnover measurements in order to assess errors in protein catabolism derived from urea turnover rates. Estimates of lean mass loss based upon urea turnover and tritiated water dilution were in general agreement, supporting estimates of protein catabolism derived from urea turnover measurements. Protein catabolism was estimated to contribute less than 4% to the average metabolic rate of suckling and fasting pups implying strict protein conservation during both periods and supporting the shypothesis that suckling pups are pre-adapted to fasting. It is proposed that strict protein conservation across suckling and fasting compensates for relative reductions in maternal investment associated with the abbreviated lactation period of the elephant seal.

Animals↗
PubMed2003

Patterns of protein carbonylation following oxidative stress in wild-type and sigB Bacillus subtilis cells.

Oxidative stress causes damage to nucleic acids, membrane lipids and proteins. One striking effect is the metal-catalyzed, site-specific carbonylation of proteins. In the gram-positive soil bacterium Bacillus subtilis, the PerR-dependent specific stress response and the sigmaB-dependent general stress response act together to make cells more resistant to oxidative stress. In this study, we analyzed the carbonylation of cytoplasmic proteins in response to hydrogen peroxide stress in B. subtilis. Furthermore, we asked whether the sigmaB-dependent response to oxidative stress also confers protection against protein carbonylation. To monitor the amount and specificity of protein damage, carbonyls were derivatized with 2,4-dinitrophenylhydrazine, and the resulting stable hydrazones were detected by immunoanalysis of proteins separated by one- or two-dimensional gel electrophoresis. The overall level of protein carbonylation increased strongly in cells treated with hydrogen peroxide. Several proteins, including the elongation factors EF-G, TufA and EF-Ts, were found to be highly carbonylated. Induction of the peroxide specific stress response by treatment with sub-lethal peroxide concentrations, prior to exposure to otherwise lethal levels of peroxide, markedly reduced the degree of protein carbonylation. Cells starved for glucose also showed only minor amounts of peroxide-mediated protein carbonylation compared to exponentially growing cells. We could not detect any differences between wild-type and deltasigB cells starved for glucose or preadapted by heat treatment with respect to the amount or specificity of protein damage incurred upon subsequent exposure to peroxide stress. However, artificial preloading with proteins that are normally induced by sigmaB-dependent mechanisms resulted in a lower level of protein carbonylation when cells were later subjected to oxidative stress.

Bacillus subtilis↗
PubMed2003

Effect of pollinator-inflicted ovule damage on floral abscission in the yucca-yucca moth mutualism: the role of mechanical and chemical factors.

The long-term persistence of obligate mutualisms (over 40 Mya in both fig/fig wasps and yucca/yucca moths) raises the question of how one species limits exploitation by the other species, even though there is selection pressure on individuals to maximize fitness. In the case of yuccas, moths serve as the plant's only pollinator, but eggs laid by the moths before pollination hatch into larvae that consume seeds. Previous studies have shown that flowers with high egg loads are more likely to abscise. This suggests that yucca flowers can select against moths that lay many eggs per flower through selective abscission of flowers; however, it is not known how yucca moths trigger floral abscission. We tested how the moth Tegeticula yuccasella triggers floral abscission during oviposition in Yucca filamentosa by examining the effects of ovipositor insertion and egg laying on ovule viability and floral abscission. Eggs are not laid at the site of ovipositor insertion: we used this separation to test whether wounded ovules were more closely associated with the ovipositor site or an egg's location. Using a tetrazolium stain to detect injured ovules, we determined whether the number of ovipositions affected the number of wounded ovules in naturally pollinated flowers. Two wounding experiments were used to test the effect of mechanical damage on the probability of floral abscission. The types of wounds in these experiments mimicked two types of oviposition-superficial oviposition in the ovary wall and oviposition into the locular cavity-that have been observed in species of Tegeticula. The effect of moth eggs on ovule viability was experimentally tested by culturing ovules in vitro, placing moth eggs on the ovules, and measuring changes in ovule viability with a tetrazolium stain. We found that ovules were physically wounded during natural oviposition. Ovules showed a visible wounding response in moth-pollinated flowers collected 7-12 h after oviposition. Exact location of wounded ovules relative to eggs and oviposition scars, as well as results from the artificial wounding experiments, showed that the moth ovipositor inflicts mechanical damage on the ovules. Significantly higher abscission rates were observed in artificially wounded flowers in which only 4-8% of the ovules were injured. Eggs did not affect ovule viability as measured by the tetrazolium stain. These results suggest that physical damage to ovules caused by ovipositing is sufficient to explain selective fruit abscission. Whether injury as a mechanism of selective abscission in yuccas is novel or a preadaptation will require further study.

Adaptation, Physiological↗
PubMed2004

Ecological stoichiometry of ants in a New World rain forest.

C:N stoichiometry was investigated in relation to diet (delta(15)N), N-deprivation, and worker body size for a diverse assemblage of tropical Amazonian ants. Relative nitrogen (N) deprivation was assayed for 54 species as an exchange ratio (ER), defined as SUCmin/AAmin, or the minimum sucrose concentration, divided by the minimum amino acid concentration, accepted as food by >/=50% of tested workers. On average, N-deprivation (ER) was almost fivefold greater for N-omnivorous and N-herbivorous (N-OH) taxa than for N-carnivores. In two-way ANOVAs at three taxonomic levels (species and species groups, genera, and tribes), higher ER was associated with small body size and (marginally) with less carnivorous diets. ERs did not differ systematically between trophobiont-tending and "leaf-foraging" functional groups, but specialized wound-feeders and coccid-tenders were prominent among high ER taxa. Paradoxically, some high ER taxa were among the most predatory members of their genera or subfamilies. Biomass % N was lower in N-OH taxa than in carnivores and varied inversely with N-deprivation (log ER) in the former taxa only. In an expanded data set, N-content increased allometrically in N-OHs, N-carnivores, and all ants combined, and with carnivory in large-bodied ants only. Exceptional taxa included small-bodied and predaceous Wasmannia, with high % N despite high ER, and Linepithema, with the lowest % N despite high delta(15)N. Patterns in C:N stoichiometry are explained largely at the genus level and above by elemental composition of alarm/defensive/offensive chemical weaponry and, perhaps in some cases, by reduced N investment in cuticle in taxa with high surface:volume ratios. Several consequences of C:N stoichiometry identify Azteca, and possibly Crematogaster, as taxa preadapted for their roles as prominent associates of myrmecophytes. C:N stoichiometry of ants should be incorporated into models of strategic colony design and examined in a phylogenetic context as opportunities permit.

Analysis of Variance↗
PubMed1991

Trypanosoma (Nannomonas) congolense: changes in respiratory metabolism during the life cycle.

All four life cycle stages (bloodstream, procyclic, epimastigote, and metacyclic) of Trypanosoma congolense IL 3000 were assayed with an oxygen electrode (polarograph) for the presence of terminal oxidases and carbon-source preference. In addition, these stages were used for histochemical analysis of mitochondrial activity using rhodamine 123, nitroblue tetrazolium, and diaminobenzidine. Morphometry was used to compare mitochondrial volumes and surface area among the different life cycle stages. It was found that in contrast to epimastigote forms, which were metabolically almost identical to procyclic forms, metacyclic forms showed characteristics of, and seemed preadapted to, differentiation into the bloodstream stage. While mitochondrial NAD+ diaphorase activity and an electrochemical potential were detected in all life cycle stages, metacyclic metabolism was glucose-based and terminal oxidase activity was primarily dependent upon the trypanosome alternative oxidase with the contribution of cyanide-sensitive respiration accounting for only 20-30% of the total respiratory capacity.

Adenosine Triphosphate↗
PubMed1994

Evolutionary patterns in life histories of Oxyurida.

The Oxyurida comprises some 850 known species that occur in the intestine of arthropods and vertebrates (one species in annelids). Important arthropod hosts include Diplopoda, Blattodea, Gryllotalpoidea, Passalidae, Scarabaeida and Hydrophilidae. The major vertebrate hosts are lizards, tortoises, primates, rodents and lagomorphs. An underlying characteristic of the group is haplodiploid reproduction and like many haplodiploid groups, pinworms tend to have life histories that involve high levels of inbreeding. Unlike Strongylida, Ascaridida and Spirurida, which have diversified in tissue site and life cycle as well as hosts, pinworms show little variation in these features and have radiated only across host groups. Two explanations are advanced for this. Haplodiploidy and its concomitant inbreeding may act to canalise evolutionary change, although diverse groups such as the Hymenoptera belie this. Alternatively, Strongylida, Ascaridida and Spirurida are presumed to have arisen from skin-penetrating ancestors that were forced to undergo a tissue migration before reaching their primitive tissue site, the gut. This migration demanded they adapt to a variety of tissue sites and thus acted as a preadaptation to further diversification. The Oxyurida, in contrast, probably arose using oral contaminative transmission. The lack of exposure to other tissue sites may therefore have relegated pinworms to their position in the posterior gut.

Animals↗
PubMed1982

Paradoxical adaptation to taste mixtures.

Quinine, sucrose, quinine-sucrose mixtures, and water were employed both as preadapting rinses and as stimuli in a factorial experiment. Human subjects judged the perceived taste intensity of the 16 stimulus-rinse pairs, which were flowed over the dorsal anterior tongue surface. Previously documented effects of adaptation, mixture suppression, and release from suppression were observed. Following adaptation to quinine-sucrose mixtures, presentation of equimolar unmixed quinine or equimolar unmixed sucrose resulted in a reliable residual bitter or sweet taste, respectively, which was significantly greater than the taste following self-adaptation of the unmixed solutions. The residual taste following mixture adaptation suggests a peripheral mechanism underlying suppression between bitter and sweet tastes in a mixture.

Adaptation, Psychological↗
PubMed1985

Role of the blue mechanism in wavelength discrimination.

The role of blue cones as well as the pathways they supply (collectively called the "blue mechanism") is evaluated by comparing ordinary wavelength discrimination functions with those obtained using two methods designed to inhibit the blue mechanism selectively. These methods use a just-noticeable-border criterion (JNB), instead of the usual one of just-noticeable-difference, and a yellow preadapting field to induce transient tritanopia. Without transient tritanopia, the data obtained using the just-noticeable-border criterion reveal a small contribution of the blue mechanism to wavelength discrimination. Transient tritanopia, with JNB, produces an additional selective loss of wavelength discrimination in a spectral region flanking 460 nm, which yields a function resembling those for tritanopes previously examined.

Color Perception↗
PubMed1995

Control of vertical eye alignment in three-dimensional space.

A target that is nearer to one eye than the other subtends a larger visual angle in the closer eye. Consequently, when making saccades between vertically separated targets that are closer to one eye, there is a vertical retinal disparity that must be overcome by a change in the relative alignment of the eyes. We recorded eye movements in three normal subjects and showed that in such viewing circumstances subjects made unequal vertical saccades that led to a rapid change (peak velocity up to 30 deg/sec) in vertical eye alignment. On average, 81% of the required change in alignment occurred within the saccade for downward movements and 47% for upward movements. Such unequal vertical saccades occurred independently of immediate disparity cues; saccades remained unequal when refixing to the remembered locations of the vertically-oriented targets, or even when the natural vertical disparity was nullified by a prism. On the other hand, when subjects wore the nullifying prism in front of the inferior visual field of the left eye for 8-20 hr, they showed a decrease in saccade disconjugacy (to 12-35% of the preadaptation value) to targets closer to the left eye in the inferior but not in the superior visual field. We suggest that the brain develops a three-dimensional map (horizontal, vertical, depth) for vertical saccade yoking, which is under adaptive control, and which is used to preprogram automatically the relative excursions of the eyes during vertical saccades as a function of the current and the desired point of regard.

Adaptation, Ocular↗
PubMed1984

Biodegradation of 4-nitrophenol in standardized aquatic degradation tests.

During the years 1978-1981 both the European Economic Community (the EEC) and the Organization for Economic Cooperation and Development (the OECD) organized various interlaboratory comparison programs on standardized screening methods to study the biodegradability of chemicals in water. While the ring test results were generally rather heterogenous, one of the compounds studied, 4-nitrophenol, turned out to be particularly problematic as the compound was found either easily biodegradable or not biodegradable by various laboratories in various tests. This paper describes some more detailed studies on 4-nitrophenol degradation in two different tests, the modified OECD screening test (MOST test) and the Zahn-Wellens test, respectively. The test variables investigated include inoculum characteristics and pretreatment, test duration, and 4-nitrophenol concentration. The results are discussed in relation to toxicity and degradation pathways of 4-nitrophenol. It is concluded that in order to improve the comparability of results from standardized aquatic biodegradation tests, test strategies should allow the option of performing a test with a preadapted inoculum in the event of negative test results with freshly collected inocula. Increasing the inoculated concentration of microorganisms in some tests may also contribute to the attainment of more consistent test results.

Biodegradation, Environmental↗
PubMed1991

The in vitro differentiation of pleomorphic Trypanosoma brucei from bloodstream into procyclic form requires neither intermediary nor short-stumpy stage.

Our studies on the in vitro differentiation of a pleomorphic Trypanosoma brucei strain TREU667 indicate that the parasite differentiates directly from long-slender into procyclic form when incubated in Cunningham's medium at 26 degrees C. The intermediary and the short-stumpy bloodstream forms harvested from infected mice can also differentiate directly into procylic form in vitro with time courses similar to that for the long-slender form. Thus, none of the three bloodstream forms appear to be significantly better preadapted for differentiation. Tricarboxylic acid (TCA) cycle intermediates cis-aconitate and L-citrate can shorten the initial lag phase of the differentiation, but an essential trigger appears to be the temperature shift from 37 degrees C to 26 degrees C, when other TCA cycle intermediates such as L-proline, L-malate, alpha-ketoglutarate, fumarate and succinate are present in Cunningham's medium. The ornithine decarboxylase (ODC) activity in T. brucei showed a gradual increase and the ODC mRNA level remained constant during the differentiation. DL-alpha-Difluoromethylornithine (DFMO), putrescine, dibutyryl cAMP and theophylline all exerted no discernible effect on the in vitro process, which suggests that neither cAMP increase nor polyamine depletion could be counted among the triggers of T. brucei differentiation. A monomorphic T. brucei strain EATRO110 was tested in the same medium at 26 degrees C but was unable to differentiate.

Animals↗
PubMed1993

Uptake and turnover of glucose in Leishmania donovani.

Glucose uptake and metabolism by Leishmania donovani promastigotes was studied using D-[14C]glucose in combination with the silicone oil centrifugation technique on organisms preadapted to different growth rates and glucose availability in the chemostat. The uptake step was differentiated from the subsequent metabolism by separation in time rather than by using non-metabolisable analogues. The uptake of glucose was measured as a function of time and/or the external glucose concentration on cells grown at high or low growth rate with glucose either as growth rate-limiting substrate, or present in excess. Glucose uptake as a function of its external concentration could be described as consisting of two components (1) a rapid equilibration owing to facilitated diffusion, followed by (2) a much slower uptake that involves an enzymatic component. This slower accumulation of label could be explained as the conversion of glucose into metabolites and a storage carbohydrate. Uptake experiments in the presence of inhibitors indicated that the conversion of glucose was an energy dependent process. These experiments indicate that the active uptake of glucose by L. donovani, as reported by others does not occur across the plasma membrane and should be reinterpreted as the intracellular conversion of glucose into metabolites and storage carbohydrate.

Animals↗
PubMed1983

Cutaneous water evaporation--II. Survival of birds under extreme thermal stress.

Two birds, the pigeon (Columba livia) and the partridge (Alectoris chukar), differing in their habits and flight ability were compared with regard to their ability to survive extreme high air temperatures (Ta's). During 270 min survival tests birds were exposed to Ta's between 45 and 60 degrees C and low relative humidities. The pigeon was observed to be unique in its ability to survive 270 min of exposure to 60 degrees C while regulating Tb at 43.8 degrees C. The partridge could not survive 270 min of exposure at Ta's exceeding 48 degrees C. The pigeons were found to be exceptional in their capacity for cutaneous evaporation. Values as high as 20.9 mg H2O/cm-2/hr were measured at 52 degrees C Ta compared to 2.4 mg H2O/cm-2/hr in the partridge. Total evaporation of the pigeon exposed to 56 degrees C Ta was about 20% higher than that in the partridge. Maximum evaporation of the pigeon exposed to 60 degrees C Ta was 34.4 mg H2O/g/hr. The significance of cutaneous water loss for survival during extreme high Ta's is discussed. It is concluded that birds as a class may be divided into two groups with regard to their physiological capacity to withstand heat stress: (1) the majority of studied species employ regular physiological mechanisms and are limited in their cooling capacity to withstand ambient temperatures 48 degrees C; (2) a few avian species, which may be of wide ecological distribution, are equipped with major physiological preadaptations to severe heat stress.

Adaptation, Physiological↗
PubMed1995

Metabolic and ventilatory adjustments and tolerance of the bat Pteropus poliocephalus to acute hypoxic stress.

We have investigated the maximum tolerance and the ventilatory responses of a bat, P. poliocephalus (PP), to normobaric hypoxic stress. PP can tolerate inspired PO2s (PiO2) down to 30 torr. This bat is one of the most hypoxia-tolerant non-hibernating species of mammals known, and has a tolerance which lies within the range of PiO2s reported for different birds. Unlike most mammals in its size range, PP maintains its normoxic oxygen consumption rate even in deep hypoxia. The maximum hypoxic ventilatory response (HVR), the air convection requirement (Vi/MO2), and the lung oxygen extraction (EL) ability of PP in deep hypoxia are all greater than those of other mammals. These and other data indicate that PP has a superior mammalian tolerance for hypocapnia. The magnitudes of both the V1/MO2 and the EL value of PP fall between those reported for Pekin ducks at corresponding PiO2s, and are inferior to the maximum capabilities of bar-headed geese. Thus, the tolerance and ventilatory adjustments of PP to deep hypoxia are intermediate between those of typical non-flying mammals and the most tolerant avian species, and suggest that at least some of this bat's respiratory adaptations for flight may serve as preadaptations for withstanding acute hypoxic stress.

Acute Disease↗