Maintenance energy demand affects biomass synthesis but not cellulase production by a mesophilicClostridium

Summary Secretion of cellulolytic activity by the mesophilClostridium strain C7 was studied while the bacterium underwent progressive carbon/energy starvation and the ensuing continuous decline in growth rate. In the slowest range of growth rates studied the organism was in full response to the global regulation imposed by guanosine 5, 3-bispyrophosphate (ppGpp). The exoenzymes of the cellulase complex were produced at the same volumetric rate whether or not the response was active. However, the volumetric rate of biomass synthesis was reduced 45% or more by the response. Energy necessary to maintain the ppGpp-regulated state (i.e., maintenance energy) was, therefore, diverted from energy going to synthesis of biomass but not from that going to exoenzyme synthesis, making the yield of cellulase activity per mole of carbon-energy substrate independent of growth rate and the exoenzyme complex produced from the substrate with equal efficiency at all growth rates. The primary consideration in improving exoenzyme productivity by bacteria with this type of energy distribution between secretion, growth, and maintenance is simply increasing yield per mole of carbon-energy substrate, with growth rate effects on yield a secondary and minimum concern.     

Exchange of colicin receptor capacity between strains of Escherichia coli sensitive or resistant to colicin K-K235

Phage and colicin-resistant mutants were derived from Escherichia coli K-12P678. Two classes of phage T6 and colicin K-resistant mutants (genotype tsx) were isolated. Tsx-2 mutants, which demonstrated mucoid growth and increased sensitivities to many antibiotics, became sensitive to colicin K when pretreated with ethylenediaminetetraacetate (EDTA), whereas Tsx-1 mutants did not. Reassociation of EDTA-released material partially restored resistance to colicin K for Tsx-2 mutants. When EDTA-released material from strain P678 was associated with either class of K-resistant mutant, an increase in colicin K sensitivity resulted. Observations suggest that colicin K can act on its target site once it penetrates the cell surface. In addition, results suggest that functional colicin K receptors can be transferred from sensitive to resistant strains, thus conferring colicin sensitivity.Non-standard Abbreviations SDS sodium dodecyl sulfate     

Effect of water stress on some oxidative enzymes and senescence in Vigna seedlings

Seedlings of Vigna catjang Endl. were subjected to water stress for 6, S and 10 days by withholding water to investigate the activities of some oxidative enzymes and the pattern of senescence in leaves of 17-day-old seedlings undergoing water stress. Increasing duration of stress produced a proportional increase in the activities of IAA-oxidase, AA-oxidase, peroxidase and glycolate oxidase but decreased catalase activity and the contents of both chlorophyll and protein, hastening senescence. Leaf water potential and relative water content were also lowered with incresing duration of stress. Permeability was increased in leaf tissue undergoing water stress for 8 days. Seed treatment with CaCl₂ (10⁻² and 10⁻¹⁴ M ) for 6 h improved the water status of leaves, decreased tissue permeability, activities of oxidative enzymes, decline of chlorophyll and protein contents and delayed senescence compared to untreated water stressed plants.     

Ultrastructural changes in the endoplasmic reticulum during dormancy release of apple embryos (Pyrus malus L.)

Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER endoplasmic reticulum - RER rough endoplasmic reticulum     

Differentiation of embryogenic pollen in cold-treated buds ofNicotiana tabacum var. Badischer burley and nutritional requirements of the isolated pollen to form embryos

Summary Embryogenic pollen were selectively isolated from buds after cold treatment at 10 °C for 10 days; it was immaterial whether the buds were taken from short day and low temperature (SD and LT; 8 hours light, 18 °C) or long day and high temperature (LD and HT; 16 hours light, 24 °C) plants. However, in buds from SD and LT plants the differentiation of embryogenic pollen could be detected as early as 7 days after the cold treatment, and pollen from these plants formed embryos at higher frequency (up to 4% of cultured pollen) than those from LD and HT plants (up to 1% only).The embryogenic pollen, in isolated buds, differentiated by way of pollen dimorphism. During cold treatment a fraction of pollen remained small, retained clear cytoplasm and was capable of embryogenesis in comparison to gametophytic pollen which enlarged and acquired granular cytoplasm. In our experiments cold treatment was a key factor in the induction of pollen dimorphism. This aspect of cold treatment in pollen embryogenesis is reported for the first time and was possible on the basis of selection of embryogenic pollen by density gradient centrifugation. The ratio of embryogenic pollen was about one fifth of the total population.The nutritional requirements of isolated pollen for embryogenesis were rather simple. These pollen formed embryos which readily developed into plantlets on a mineral medium supplemented with sucrose provided the pH was 6.8.     

Survival of Chromatium vinosum at low light intensities

The effect of low irradiation on the viability of Chromatium vinosum was investigated. Cultures were precultivated at 1,000 lux (=0.1/h). Then, before the substrate was depleted, illumination was changed to either complete darkness or about 30 lux. Previously, the latter light intensity had been found not to promote growth.The parameters assayed were viability, protein, bacteriochlorophyll, ATP, RNA, DNA, absorbance (E ₂₆₀) of the supernatant, and total anthron-positive material.The data show that irradiation insufficiently high to promote growth, results in viability percentages as high as 90% after 8 days, whereas cultures incubated in complete darkness are virtually dead by then. Neither in the light nor in the dark a degradation of protein or cell wall hexoses was observed. The RNA content also remained constant. However, particularly in the dark cultures DNA was found to decrease concomitant with increased E ₂₆₀ readings of the supernatant. It is considered unlikely that such essential macromolecules are degraded to serve the maintenance energy requirements. The ecological impact of the observations is discussed.Non-Standard Abbreviations PHB poly--hydroxybutyric acid - Bchl Bacteriochlorophyll     

Energy requirements for growth and maintenance of Scenedesmus protuberans Fritsch in light-limited continuous cultures

Scenedesmus protuberans Fritsch was grown in light-limited continuous cultures with a light-dark cycle, at temperatures of 20° and 28° C. At 20° irradiances of 12 and 38 W m^–2 were used, at 28° 38 W m^–2.The relationships between growth rate and light uptake rate were of diphasic linear character. With the lower growth rates the relationships were defined with the parameters _e , i.e. the specific maintenance rate constant, and c, the true efficiency of light energy conversion into biomass. The _e -value was dependent on temperature, the c on irradiance.In cultures, incubated in prolonged darkness, decrease rates of biomass were comparable to the derived _e -values.Both diphasic linear relationships between growth rate and light uptake rate and the same order of magnitude of _e -values could be derived from literature data on other green algae.     

Magnesium (and trace substance) deficiencies in the pathogenesis of cancer

Except for a few experimental models of magnesium (Mg)-deficiency-induced neoplasms, less attention has been paid in the past quarter century in the Western world to this macromineral than to the trace elements; e.g., selenium (Se) and zinc (Zn), and to vitamins, deficiencies of which are each considered probable factors in oncogenesis. Although early epidemiologic studies showed an inverse correlation between the amount of Mg in soil and water and the incidence of (gastric) cancer, and several animal studies supported the premise that Mg has a prophylactic effect against induction of cancer, other studies showed that Mg supplementation increased the growth of established experimental tumors. Thus, enthusiasm for this approach subsided. The early epidemiologic findings have since been confirmed, and there have been studies demonstrating the importance of Mg in maintaining immunocompetence, and others indicating that immunodeficiencies increase susceptibility to the development of cancer. Evidence has now accrued that indicates that Mg deficiency increases susceptibility to chemical oncogens. The abnormal metabolism of tryptophan (yielding a carcinogenic metabolite) that indicates functional or absolute pyridoxine deficiency is an indirect clue to Mg deficiency. Vitamin B₆-activated enzymes require Mg as a cofactor. However, the early warnings against the use of Mg as part of an antineoplastic program against established cancer were justified, since rapidly metabolizing cells (such as cancers) are dependent on Mg. There are similarities between experiences with Mg and with Se and Zn. All three are required for normal metabolism; Se also protects against free radicals in the environment. Mg and Zn have increased established tumor growth, and their depletion has been applied to antineoplastic programs, with risks comparable to those of using antimetabolic agents.     

Growth and energy production in Bacteroides amylophilus

The molar growth yield (Y _m) of Bacteroides amylophilus strain WP91 on maltose was 68±2 g/mol when determined from batch cultures at the peaks of maximal growth. Continued incubation led to considerable cell lysis. When calculated from batch cultures in exponential phase (specific growth rate, =0.57 h^-1) Y _m was 101 g/mol. The maximum value of Y _m in maltose-limited chemostat cultures at the maximum dilution rate (D) attainable (D==0.39 h^-1) was about 79 g/mol. Ammonia-Fmited chemostat cultures metabolized maltose with a much reduced efficiency and this was associated with a difference in morphology and chemical composition of the cells. The theoretical maximum molar growth yields (Y _m ^max ) were 55 and 114 g/mol for ammonia- and maltose-limited growth respectively. However, if account was taken of extracellular nitrogen-containing material in ammonia-limited cultures, Y _m ^max became 60. The maintenance coefficient (m _s), estimated from the lines relating the specific rate of maltose consumption (q _m) and D (where m _s=q _m at D=0), was 7.4±0.6×10^-4 mol maltose/g x h for both nutrient limitations. A difference in maintenance energy demand, independent of growth-rate, could not account, therefore, for the observed differences in Y _m between ammonia- and maltose-limited growth.