Fungal parasitism in a freshwater copepod: Components of the interaction between Aphanomyces and Boeckella

The transmission of Aphanomyces infection among carriers (host females), host mortality, recovery from infection, and stages in the infection process were investigated in Boeckella dilatata (Copepoda: Calanoida) at 15°C in the laboratory. Over a 4-week period, 57.9% female B. dilatata became infected after being paired with carrier females and 3.8% lost their infection hyphae. Mortality was higher among carrier females (41%) than noncarriers (18.2%) but may be related to the age of the females. There was no difference in body size or clutch size between carrier and noncarrier females. However, host females carried clutches for shorter periods and had correspondingly longer intervals between clutches than did noncarriers. The time course of development of infection at 15°C is described.     

Regional Quantitation of Preprodynorphin mRNA in Guinea Pig Gastrointestinal Tract

The endogenous opioid peptide dynorphin has been shown by immunochemical studies to be widely distributed in the gastrointestinal tract. The aim of this study was to determine basal levels of preprodynorphin (ppDyn) mRNA in different regions of the gastrointestinal tract of the guinea pig. A modified sensitive and specific solution hybridization RNase protection assay was used to quantitate ppDyn mRNA, with confirmation by gel analysis of the RNase protected hybrids and PCR amplified cDNA. This method combines high sensitivity and sufficient throughput to analyze large number of samples in a single assay. Low but measurable amounts of ppDyn mRNA were detected in fundus, duodenum, jejunum, ileum, cecum, and rectum. The rectum contained significantly more ppDyn mRNA than the stomach, small bowel, and cecum. The muscularis/myenteric plexus layer of both ileum and rectum contained a higher concentration of ppDyn mRNA per g total RNA compared to the mucosa/submucosa/submucosal plexus. However, a greater absolute amount of ppDyn mRNA (80–85%) localized to the mucosal layer. The greater absolute amount of ppDyn mRNA in the mucosal layer may indicate the presence of dynorphin in the endocrine cells of the mucosa.     

Zur Morphogenese des respiratorischen Epithels der Tracheenkiemen bei Larven der Limnephilini KOL. (Insecta,Trichoptera)

Zusammenfassung Das respiratorische Epithel der Tracheenkiemen ist durch ein hochgeordnetes Tracheolengerüst charakterisiert. Die Tracheolen liegen parallel zur Längsachse der fadenförmigen Tracheenkiemen dicht unter der Cuticula in statistisch gleichmäßigem Abstand zueinander. Die Regelmäßigkeit dieses subcuticularen Tracheolengerüsts weist auf ein physiologisch optimal arbeitendes System hin. Der Abstand zwischen zwei Tracheolen ist sehr wahrscheinlich gleich dem doppelten Radius der tracheolaren Einzugsgebiete. Auf diese Weise wird bei einem Minimum an Tracheolenmaterial der gesamte diffundierende Sauerstoff der respiratorischen Oberfläche von den Tracheolen erfaßt. Die Morphogenese dieser Strukturregelmäßigkeit wird während der larvalen Entwicklung verfolgt. Dabei zeigt sich, daß mit jeder Häutung zahlreiche neue Tracheolen in das respiratorische Epithel geordnet eingebaut werden und die Abstände zwischen den Tracheolen in Korrelation zum Radius der Tracheolen von Larvenstadium zu Larvenstadium geregelt abnehmen.

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Morphogenesis of the respiratory epithelium in the tracheal gills of larval Limnephilini KOL. (Insecta, Trichoptera)

Summary The respiratory epithelium of the tracheal gills of the larval Limnephilini KOL. (Insecta, Trichoptera) is characterized by a highly organized tracheolar framework. The tracheoles are found parallel to the longitudinal axis of the thread-like tracheal gills and lie closely underneath the cuticle at statistically uniform distances. The regular distribution of the subcuticular tracheoles represents an optimum physiological system with the tracheolar interspace probably corresponding to twice the radius of the tracheolar catchment area. This arrangement ensures that all oxygen diffusing across the respiratory gill surface is taken up by the tracheoles with a minimum of tracheolar material. The morphogenesis of this regular distribution was studied during the larval development. With each moult numerous new tracheoles are added to the regular distribution. The distances between the tracheoles decrease regularly in correlation to the decreasing radius of the tracheoles from one larval stage to the next.

     

Dark recovery of UV-irradiated phage T1 I. A minor recovery effect whose exclusion permits the study of survival kinetics under presumably repairless conditions

The survival of UV-irradiated phage T1 is much lower in excision repair-deficient than in excision repair-proficient E. coli cells, due to lack of “host cell reactivation” (HCR). An additional decrease in phage survival occurs when repair-deficient (HCR⁻) host cells have been exposed to UV doses from 3000–10 000 erg mm⁻² of 254 nm UV-radiation prior to infection. The observed effect is attributed to loss of a minor phage recovery process, which requires neither the bacterial excision repair nor the bacterial REC repair system. This type of recovery is little affected by caffeine or acriflavine at concentrations that preclude HCR completely. Its full inhibition by UV-irradiation of the cells requires an approximately 8 times larger dose than complete inhibition of HCR.

In heavily preirradiated cells, the T1 burst size is extremely small and multiplicity reactivation is considerably less extensive than in unirradiated cells. Presumably the survival of singly infecting T1 in these cells reflects absence of any type of repair. The observed phage sensitivity and shape of the curve are compatible with the expectation for completely repairless conditions. The mechanism underlying the minor recovery is not known; theoretical considerations make a phage REC repair mechanism seem likely.     

Complex II phosphorylation is triggered by unbalanced redox homeostasis in cells lacking complex III

A marked stimulation of complex II enzymatic activity was detected in cybrids bearing a homoplasmic MTCYB microdeletion causing disruption of both the activity and the assembly of complex III, but not in cybrids harbouring another MTCYB mutation affecting only the complex III activity. Moreover, complex II stimulation was associated with SDHA subunit tyrosine phosphorylation. Despite the lack of detectable hydrogen peroxide production, up-regulation of the levels of mitochondrial antioxidant defenses revealed a significant redox unbalance. This effect was also supported by the finding that treatment with N-acetylcysteine dampened the complex II stimulation, SDHA subunit tyrosine phosphorylation, and levels of antioxidant enzymes. In the absence of complex III, the cellular amount of succinate, but not fumarate, was markedly increased, indicating that enhanced activity of complex II is hampered due to the blockage of respiratory electron flow. Thus, we propose that complex II phosphorylation and stimulation of its activity represent a molecular mechanism triggered by perturbation of mitochondrial redox homeostasis due to severe dysfunction of respiratory complexes. Depending on the site and nature of the damage, complex II stimulation can either bypass the energetic deficit as an efficient compensatory mechanism, or be ineffectual, leaving cells to rely on glycolysis for survival.     

Cytochromes bd-I and bo3 are essential for the bactericidal effect of microcin J25 on Escherichia coli cells

Microcin J25 has two targets in sensitive bacteria, the RNA polymerase, and the respiratory chain through inhibition of cellular respiration. In this work, the effect of microcin J25 in E. coli mutants that lack the terminal oxidases cytochrome bd-I and cytochrome bo₃ was analyzed. The mutant strains lacking cytochrome bo₃ or cytochrome bd-I were less sensitive to the peptide. In membranes obtained from the strain that only expresses cytochrome bd-I a great ROS overproduction was observed in the presence of microcin J25. Nevertheless, the oxygen consumption was less inhibited in this strain, probably because the oxygen is partially reduced to superoxide. There was no overproduction of ROS in membranes isolated from the mutant strain that only express cytochrome bo₃ and the inhibition of the cellular respiration was similar to the wild type. It is concluded that both cytochromes bd-I and bo₃ are affected by the peptide. The results establish for the first time a relationship between the terminal oxygen reductases and the mechanism of action of microcin J25.     

Taxonomic distribution,structure/function relationship and metabolic context of the two families of sulfide dehydrogenases: SQR and FCSD

Hydrogen sulfide (H₂S) is a versatile molecule with different functions in living organisms: it can work as a metabolite of sulfur and energetic metabolism or as a signaling molecule in higher Eukaryotes. H₂S is also highly toxic since it is able to inhibit heme cooper oxygen reductases, preventing oxidative phosphorylation. Due to the fact that it can both inhibit and feed the respiratory chain, the immediate role of H₂S on energy metabolism crucially relies on its bioavailability, meaning that studying the central players involved in the H₂S homeostasis is key for understanding sulfide metabolism.Two different enzymes with sulfide oxidation activity (sulfide dehydrogenases) are known: flavocytochrome c sulfide dehydrogenase (FCSD), a sulfide:cytochrome c oxidoreductase; and sulfide:quinone oxidoreductase (SQR).In this work we performed a thorough bioinformatic study of SQRs and FCSDs and integrated all published data. We systematized several properties of these proteins: (i) nature of flavin binding, (ii) capping loops and (iii) presence of key amino acid residues. We also propose an update to the SQR classification system and discuss the role of these proteins in sulfur metabolism.