Biochemical and physiological aspects of differentiation in the fungi

Growth and sporulation stoichiometry and kinetics of Coniothyrium minitans on agar media

Coniothyrium minitans was cultivated on agar media with different concentrations of starch, urea, and trace elements. By means of elemental balances, the stoichiometry of growth and sporulation was established. C. minitans produced byproducts on all media, especially in the medium with high urea concentrations, where 30% of the starch was converted into byproducts. Simple empirical models were used to describe the kinetics of growth, sporulation, CO(2) production, and substrate consumption on all media. Total biomass and mycelium could be described reasonably well with the logistic law. Starch, urea, and oxygen consumption and CO(2) production could be described as a function of total biomass by the linear-growth model of Pirt. There were almost no differences between media for the estimates of yield coefficients and maintenance coefficients. Only at high urea concentrations were maintenance coefficients much higher. Similar to substrate consumption and CO(2) production, the kinetics of sporulation could be described as a function of mycelium production with the linear-growth model. It is shown that sporulation of C. minitans is growth-associated. Based on kinetics, the process costs for producing spores are roughly calculated. In addition, it is shown that fermentor costs represent the majority of production costs.

Response of Rhizopus oligosporus to temporal temperature profiles in a model solid-state fermentation system

Membrane overcultures of Rhizopus oligosporus were shifted from 37 to 50 degrees C for 10 h and then returned to 37 degrees C, mimicking the temporal temperature profiles which typically occur in SSF due to heat transfer limitations. Analysis with a modified two-phase growth model suggests that the temperature upshift causes a 48% decrease in the number of actively extending hyphal tips, and that the first order death rate constant of tips increases from 0. 059 to 0.073 h(-1). The fungus did not immediately recover when the temperature was returned to 37 degrees C. The model assumed that the specific growth rate constant microgram(g) was not affected by the increase of temperature, although contradictory data was obtained from radial growth rate experiments.

Medium optimization for spore production of coniothyrium minitans using statistically-based experimental designs

Statistically-based experimental designs were used to optimize a chemically defined solid medium for the spore production of Coniothyrium minitans. In the first optimization step the influence of starch, urea, phosphate, magnesium, calcium, thiamin and trace elements on spore production was evaluated using a fractional factorial design. Starch and trace elements influenced spore production positively while urea affected spore production negatively. The other components had no significant influence on spore production. In the second and third steps the concentrations of starch, urea and trace elements were further optimized using central composite designs and response surface analysis. This optimization strategy allowed the spore production to be increased by a factor 7 from 4 x 10(9) to almost 3 x 10(10) spores per Petri dish of 9 cm diameter. Copyright 1999 John Wiley & Sons, Inc.

Oxidation of carbon sources via the tricarboxylic acid cycle during calcium-induced conidiation of Penicillium notatum

The TCA cycle was examined during Ca2+-induced conidiation in Penicillium notatum over the 12-h period after addition of Ca2+ to vegetative cultures. Conidiation was independent of Ca2+ when certain intermediates and derivatives of the TCA cycle served as sole carbon sources. Arsenite and malonate augmented the effect of Ca2+ on conidiation but did not substitute for it. Mitochondria from vegetative cells had low rates of oxidation of TCA cycle intermediates and, with the exception of pyruvate, aconitate and glutamate, these were poorly linked to phosphorylation processes. Calcium ions affected mitochondrial function causing reduced oxidation of oxoglutarate, elimination of pyruvate oxidation and a decline in respiratory control of these substrates with increased oxidation of NADH and NADPH. Radiorespirometric studies and enzyme searches revealed a complete but weakly oxidative TCA cycle in vegetative cells. In Ca2+-induced cells oxoglutarate dehydrogenase activity was deleted within 6.5 h of Ca2+ addition and this was accompanied by establishment of an 'incomplete Krebs cycle'. Calcium-induced conidiation was associated with increased capacity for acetate and glutamate metabolism involving an activated glyoxylate shunt which may be related to enhanced biosynthetic demand. The metabolic basis of the Ca2+ effect on conidiation is discussed in connection with previous findings.

Anaplerotic metabolism of Aspergillus nidulans and its effect on biomass synthesis in carbon limited chemostats

Anaplerotic fixation of carbon dioxide by the fungus Aspergillus nidulans when grown under carbon-limited conditions was mediated by pyruvate carboxylase and a phosphoenol pyruvate (PEP)-metabolising enzyme which has been tentatively designated as PEP carboxylase. The activities of both enzymes were growth rate dependent and measurements of H14CO3 incorporation by growing mycelium indicated that they were responsible for almost all the assimilated carbon dioxide. In carbon-limited chemostats, the maximum rate of bicarbonate assimilation occurred at a dilution rate of 0.11 h-1, equivalent to 1/2 micromax. The affinity of the pyruvate carboxylase for bicarbonate was twice that of the PEP carboxylase under the conditions of growth used. The effect of changing the bicarbonate concentration in carbon-limited chemostats was substantial: increasing the HCO-3 concentration over the range 0.7 - 2.8 mM enhanced biomass synthesis by 22%. Over-shoots in bicarbonate assimilation and carboxylase activity occurred when steady state chemostat cultures were subjected to a step down in dilution rate.

Secondary metabolism as an expression of microbial growth and development

A case is made out for regarding secondary metabolism as part of normal cell growth, related to its interactions with the environment. Secondary metabolism is widespread, especially in fungi and actinomycetes, and is not to be regarded as confined to the production of antibiotics and other special substances. It is part of the normal maturation process. Examples are given of the influence of secondary metabolism in ecological systems. It is also shown that cell productivity can be related to age structure. Secondary metabolism is thus linked with growth, although in many cases this may not be obvious in laboratory work. Initiation of production will arise from the system which regulates growth and differentiation. These processes are little understood at present, but it is clear that the factors involved differ in different instances and that they involve a very great variety of biochemical and physiological processes.

Regulation of periodicity and intensity of photo-induced conidiation of Trichoderma viride

After a short irradiation at 366 nm with 200 lx, the intensity of conidiation of Trichoderma viride colonies grown in the dark increased for the first 10 s proportionally with time. The increase slowed down after 10 s-5 min of exposure and after 10-60 min of irradiation the conidiation intensity began to decrease. When photo-induced by daylight, the conidiation started at a high rate after 25 h and persisted even after 48 h. The conidiation had no circadian character and its periodicity depended on the periodicity of photo-induction. Its intensity was also influenced by the carbon sources used, a maximum being reached with glucose (1-2%). Higher glucose concentrations inhibited conidiation but had no influence on growth of colonies.

Variation in levels of enzymes related to energy metabolism in alternative developmental pathways of Blastocladiella emersonii

The activities of phosphofructokinase (PFK), fructose diphosphatase (FDP), nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP)-linked isocitrate dehydrogenases (IDHNAD, IDHNADP), two NAD-linked glutamate dehydrogenases (GDH1, GDH2), and isocitrate lyase were studied during the development of the two phenotypes, ordinary colorless and resistant sporangia (OC and RS plants), of water mold Blastocladiella emersonii in synchronized liquid cultures. The OC plants had a generation time of about 12 h, whereas the RS plants required 3.5 days to reach maturity. All the enzymes were present throughout the development of both phenotypes. In zoospores, PFK, FDP, and GDH2 were localized in the cytosol. The IDHNADP activity was distributed with two-thirds in the soluble and one-third in the particulate fraction. GDH1 and IDHNAD showed the same distribution and were predominantly present in the particulate fraction, presumably in the mitochondria. Isocitrate lyase was found in the particulate fraction. The enzyme levels changed considerably during development. FDP and IDHNADP varied in a parallel manner. Similarly, the three enzymes PFK, IDHNAD and GDH1 showed parallel variations. The activity patterns for all enzymes were different for the OC and RS pathways. Isocitrate lyase exhibited the largest changes in activity during development. Thus, during OC plant formation, its activity decreased by a factor of 20. GDH2 varied similarly to PFK and IDHNADP during OC plant development, whereas it behaved like isocitrate lyase during RS plant development. The ratios between anabolic and catabolic enzymes were higher in mature plants than in zoospores and higher in RS plants than in OC plants. The results indicate that the variations in the enzyme levels are secondary to the critical changes involved in the transition from one developmental pathway to the other.

Growth and differentiation of the water mold Blastocladiella emersonii: cytodifferentiation and the role of ribonucleic acid and protein synthesis

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Effects of oxygen and glucose on energy metabolism and dimorphism of Mucor genevensis grown in continuous culture: reversibility of yeast-mycelium conversion

Mucor genevensis was grown in both glucose-limited and glucose-excess continuous cultures over a range of dissolved oxygen concentrations (<0.1 to 25 muM) to determine the effects of glucose and the influence of metabolic mode (fermentative versus oxidative) on dimorphic transformations in this organism. The extent of differentiation between yeast and mycelial phases has been correlated with physiological and biochemical parameters of the cultures. Under glucose limitation, oxidative metabolism increased as the dissolved oxygen concentration increased, and this paralleled the increase in the proportion of the mycelial phase in the cultures. Filamentous growth and oxidative metabolism were both inhibited by glucose even though mitochondrial development was only slightly repressed. However, the presence of chloramphenicol in glucose-limited aerobic cultures inhibited mitochondrial respiratory development but did not induce yeast-like growth, indicating that oxidative metabolism is not essential for mycelial development. Once mycelial cultures had been established under aerobic, glucose-limited conditions, subsequent reversal to anaerobic conditions or treatment with chloramphenicol caused only a limited reversal (<35%) to the yeast-like form. Glucose, however, induced a complete reversion to yeast-like form. It is concluded that glucose is the most important single culture factor determining the morphological status of M. genevensis; mitochondrial development and the functional oxidative capacities of the cell appear to be less important factors in the differentiation process.

The biosynthesis of plasmodial myosin during starvation of Physarum polycephalum

The actomyosin protein complex of Physarum polycephalum was prepared from vegetative and starved plasmodia. The yield of actomyosin per unit wet wt. was the same from both types of plasmodia. Myosin was resolved from the complex by gel filtration and purified by ion-exchange chromatography. The Ca(2+)-stimulated adenosine triphosphatase activities of myosin preparations from vegetative and starved plasmodia were not appreciably different. Synthesis of myosin de novo was shown to occur during the starvation phase of the life-cycle by the isolation of labelled myosin preparations from plasmodia starved in the presence of [2-(14)C]glycine. Fractionation of polyacrylamide gels after gel filtration of labelled myosin confirmed the presence of label in the adenosine triphosphatase-active myosin band. It is concluded that during starvation myosin synthesis continues although there is a net loss of approx. 50% of the total protein. Sodium dodecyl sulphate-polyacrylamide-gel electrophoresis of Physarum myosin showed the presence of low-molecular-weight components of the molecule, similar to those of muscle myosins. The content and composition of the free amino acid pool of Physarum was measured at various time-intervals during the vegetative and starvation phases of the life-cycle.

Phenotypes of pleiotropic-negative sporulation mutants of Bacillus subtilis

The phenotypic properties of representatives of the five genetic classes of pleiotropic-negative sporulation mutants have been investigated. Protease production, alkaline and neutral proteases, was curtailed in spoA mutants, but the remainder of mutant classes produced both proteases, albeit at reduced levels. The spoA and spoB mutants plaqued phi2 and phi15 at high efficiency, but the efficiency of plating of these phages on spoE, spoF, and spoH mutants was drastically reduced. Antibiotic was produced by the spoH mutants and to a degree by some spoF mutants, but the other classes did not produce detectable activity. The spoA mutants were less responsive to catabolite repression of histidase synthesis by glucose than was the wild type. Severe catabolite repression could be induced in spoA mutants by amino acid limitation, suggesting that the relaxation of catabolite repression observed is not due to a defect in the mechanism of catabolite repression. Although others have shown a perturbation in cytochrome regulation in spoA and spoB mutants, the primary dehydrogenases, succinate dehydrogenase and reduced nicotinamide adenine dinucleotide dehydrogenase, leading to these cytochromes are unimpaired in all mutant classes. A comparison of the structural components of cell walls and membranes of spoA and the wild type is made. The pleiotropic phenotypes of these mutants are discussed.

Levels of glycogen and trehalose in Mycobacterium smegmatis and the purification and properties of the glycogen synthetase

The levels of glycogen, free trehalose, and lipid-bound trehalose were compared in Mycobacterium smegmatis grown under various conditions of nitrogen limitation. In a mineral salts medium supplemented with yeast extract and containing fructose as the carbon source, the accumulation of glycogen increased dramatically as the NH(4)Cl content of the medium was lowered. However, levels of free trehalose remained relatively constant. Cells were grown in low nitrogen medium and were then shifted to medium containing high nitrogen. Under these conditions, there was a rapid accumulation of glycogen in low nitrogen, and this glycogen was rapidly depleted when cells were placed in high nitrogen medium. Again the concentration of free trehalose remained fairly constant. However, when cells were grown in low nitrogen medium with [(14)C]fructose and then transferred to high nitrogen medium with unlabeled fructose, the specific radioactivity (counts per minute per micromole) of the free trehalose fell immediately, indicating that it was being synthesized and turned over continually. On the other hand, the specific radioactivity of the glycogen and bound trehalose declined much more slowly, suggesting that these two compounds were not turning over as rapidly or were being synthesized at a much slower rate. Experiments on the incorporation of [(14)C]fructose into glycogen and trehalose indicated that cells in high nitrogen medium synthesized much less glycogen than those in low nitrogen. However, synthesis of both free trehalose and bound trehalose was the same in both cases. The specific enzymatic activities of the glycogen synthetase and the trehalose phosphate synthetase varied somewhat from one growth condition to another, but there was no correlation between enzymatic activity and the amount of glycogen or trehalose, suggesting that changes in glycogen levels were not due to increased synthetic capacity. The glycogen synthetase was purified about 35-fold and its properties were examined. This enzyme was specific for adenosine diphosphate glucose as the glucosyl donor.