Variation in yeast mitochondrial activity associated with asci

An increase in mitochondrial membrane potential (DeltaPsim) and mitochondrially produced 3-hydroxy (3-OH) oxylipins was experienced in asci of the nonfermentative yeasts Galactomyces reessii and Lipomyces starkeyi and the fermentative yeasts Pichia farinosa and Schizosaccharomyces octosporus. Strikingly, asci of Zygosaccharomyces bailii showed no increase in mitochondrial activity (DeltaPsim and oxylipin production). As expected, oxygen deprivation only inhibited ascus formation in those yeasts with increased ascus mitochondrial activity. We conclude that ascus formation in yeasts is not always dependent on mitochondrial activity. In this case, fermentation may provide enough energy for ascus formation in Z. bailii.     

The distribution and taxonomic value of fatty acids and eicosanoids in the Lipomycetaceae and Dipodascaceae

Using radioimmunoassay, blood platelet aggregation studies and GC-MS the existence of prostaglandins in the endomycetalean yeastDipodascopsis uninucleata was confirmed by our group. These findings triggered the search for similar eicosanoids in the rest of the Endomycetales. We commenced by scanning for the easily detectable precursors of eicosanoids, linoleic- and linolenic acid. We selected two families (i.e. Lipomycetaceae and Dipodascaceae), both producing these precursors, for further investigation.Representative strains of the two families were tested for their ability to grow in the presence of 1mM aspirin, a specific inhibitor of prostaglandin biosynthesis. In contrast to the lipomycetaceous species the dipodascaceous species were insensitive to this drug. These results were verified when representative strains of both families were investigated for their ability to produce eicosanoids from externally fed radio-labeled arachidonic acid along an aspirin sensitive pathway. Thin layer chromatography of culture extracts, followed by autoradiography, showed that while none of the Dipodascaceae produced aspirin sensitive arachidonic acid metabolites, the members of the Lipomycetaceae tested positive for these metabolites. These findings supported the separation of the lipomycetaceous yeastDipodascopsis from the Dipodascaceae. The findings also correlate with the delimitation of these yeasts in two families (i.e. Dipodascaceae and Lipomycetaceae).Further investigation indicated that prostaglandin production by the genusDipodascopsis is mainly associated with ascosporogenesis. Thin layer chromatography of cell extracts fromDipodascopsis tóthii, followed by scintillation counting, indicated the presence of PGF₂ and PGE₂ during ascosporogenesis.     

The effect of acetic acid concentration on the growth and production of gamma-linolenic acid byMucor circinelloides CBS 203.28 in fed-batch culture

The effect of different initial acetic acid concentrations on the growth of and lipid and gamma-linolenic acid (GLA) production byMucor circinelloides CBS 203.28 was determined in a 14 litre stirred tank reactor operated in a fedbatch, pH-stat mode with acetic acid as carbon source and pH titrant. Increased acetic acid concentrations in the culture resulted in a significant increase in the crude oil content of the biomass. By contrast, all the other parameters such as the biomass concentration, GLA and oil yield on acetic acid, the GLA content of the biomass and oil, the growth rate and volumetric rate of GLA production decreased with an increase in acetic acid concentration. The best results were obtained with acetic acid at 2 g/1, which gave 39.8 mg GLA/g biomass and 15.6% GLA in the neutral lipid fraction, amounting to 340 mg GLA/1 culture. A decrease in the glyco- and phospho-lipid fractions during the cultivation coincided with an increase in the neutral lipid fraction. The GLA content of the biomass remained within rather narrow limits of 3.5% to 4% of the biomass, irrespective of the oil content of the biomass. The fatty acid profile was not greatly affected by the acetic acid concentration. The hyphae of the fungus were characterized by the accumulation of large intracellular oil droplets and some septa delimited the hyphae.     

Do grazing caddisfly larvae of Melampophylax mucoreus (Limnephilidae) use their antennae for olfactory food detection?

Abstract. The behaviour of larvae of Melampophylax mucoreus (Limnephilidae; Trichoptera) is studied to test their capacity for food detection over long distances by olfaction. In aquaria experiments with stagnant water, the larvae rapidly accumulate on a biofilm-covered stone (offered food patch) but not on control stones without biofilm-cover. Larvae in an artificial flow channel (flume), with uni-directional flow between an arrangement of stones covered with biofilm and stones without biofilm, can find food patches upstream from their location more rapidly than downstream. Stimuli transported towards the larvae by the water current might assist food location. However, no significant differences could be found in the movement of larvae with intact antennae compared with larvae without antennae. The results lead to the conclusion that the larvae of M. mucoreus find food patches mainly by random movement, which is assisted by their high mobility. Long-distance olfactory orientation towards food patches, mediated by antennae, can be precluded. Gustatory stimuli appear to play an important role in contact-chemoreception to identify biofilm patches on stone surfaces. Scanning electron microscopy studies of the larval head reveal that the antennae of M. mucoreus are small pegs (50 µm in length) with an apical plate (15 µm in diameter). The mouthparts of the larvae, especially the maxillary palps, show a variety of different sensilla types that are possibly used for contact-chemoreception. These sensilla also could be responsible for the orientation towards a food resource upstream of the larvae.     

MSC-DC interactions: MSC inhibit maturation and migration of BM-derived DC

BACKGROUND: Mesenchymal stromal cells (MSC) comprise one of the BM stromal cells that are known to support hematopoiesis. It has also been suggested recently that MSC display immunosuppressive capacities through inhibiting the differentiation of monocyte-derived DC. DC travel to the lymph nodes (LN) to present Ag to T cells, and CCL21 is the chemokine that plays an important role in DC migration into the T-cell area of LN. We addressed the effect of MSC on this chemotactic activity of DC, one of the typical characteristics upon maturation. METHODS: BM cells were isolated and then cultured for generation of myeloid DC in the presence of GM-CSF and/or lipopolysaccharide with or without MSC. MSC were identified by flow cytometry of the immunologic markers and by performing colony-forming unit fibroblast assay. Migration of DC was observed with a newly developed time-lapse video microscopic technique. RESULTS: MSC co-culture inhibited the initial differentiation of DC, as well as their maturation. The matured DC actively migrated directionally in response to CCL21, a powerful DC-attracting chemokine, whereas the MSC co-cultured DC did not. DISCUSSION: Collectively, the findings of these experiments raise the possibility that MSC suppress the migratory function of DC and so they may serve immunoregulatory activities through the modulation of the Ag-presenting function of DC.     

Molecular characterization of European and Egyptian isolates of Sclerotium cepivorum,the incitant of onion white rot

Abstract

The tested European and Egyptian isolates of Sclerotium cepivorum were able to infect Giza 6 onion cultivar causing white rot disease with a different degrees of disease severity (ranging from sever to weak). The pattern of esterase isozymes produced by the tested isolates of the pathogen showed two main bands (arrows) which were different in density. Such differences in density of bands were present in every run and therefore appear to be indicators for differences among the tested isolates. Analysis of the protein pattern of the tested isolates of the pathogen indicated that the tested isolates had major proteins of a molecular weight of 52, 36, 23 and 16 kDa. Variation between isolates was detected by presence of bands of low molecular weight. Isolate Nos. 1, 4, 5, 7, 8, 9, 10 and 13 had a band at 17 kDa, whereas isolate Nos. 2, 3, 6, 11, 12, 14, and 15 had a band at 20 kDa. Using RAPD analysis to evaluate the genetic diversity of the tested isolates indicated that the tested field population of the pathogen was genetically heterogeneous but shared a number of common bands with molecular weights ranging from 650 to 2500 bp. Based on the DNA banding pattern the tested isolates can be assigned to seven genetically different groups. All tested isolates produced a band at 2500 bp except isolate No. 7. No correlation was exibited between patterns esterase isozmes, protein and DNA patterns of S. cepivorum isolates and their virulence or geographical origin.     

Practical identifiability of biokinetic parameters of a model describing two-step nitrification in biofilms

Parameter estimation and model calibration are key problems in the application of biofilm models in engineering practice, where a large number of model parameters need to be determined usually based on experimental data with only limited information content. In this article, identifiability of biokinetic parameters of a biofilm model describing two-step nitrification was evaluated based solely on bulk phase measurements of ammonium, nitrite, and nitrate. In addition to evaluating the impact of experimental conditions and available measurements, the influence of mass transport limitation within the biofilm and the initial parameter values on identifiability of biokinetic parameters was evaluated. Selection of parameters for identifiability analysis was based on global mean sensitivities while parameter identifiability was analyzed using local sensitivity functions. At most, four of the six most sensitive biokinetic parameters were identifiable from results of batch experiments at bulk phase dissolved oxygen concentrations of 0.8 or 5 mg O(2)/L. High linear dependences between the parameters of the subsets (KO2,AOB,muAOB) and (KO2,NOB,muNOB) resulted in reduced identifiability. Mass transport limitation within the biofilm did not influence the number of identifiable parameters but, in fact, decreased collinearity between parameters, especially for parameters that are otherwise correlated (e.g., muAOB) and KO2,AOB, or muNOB and KO2,NOB). The choice of the initial parameter values had a significant impact on the identifiability of two parameter subsets, both including the parameters muAOB and KO2,AOB. Parameter subsets that did not include the subsets muAOB and KO2,AOB or muNOB and KO2,NOB were clearly identifiable independently of the choice of the initial parameter values.