Enhancing vector refractoriness to trypanosome infection: achievements,challenges and perspectives

With the absence of effective prophylactic vaccines and drugs against African trypanosomosis, control of this group of zoonotic neglected tropical diseases depends the control of the tsetse fly vector. When applied in an area-wide insect pest management approach, the sterile insect technique (SIT) is effective in eliminating single tsetse species from isolated populations. The need to enhance the effectiveness of SIT led to the concept of investigating tsetse-trypanosome interactions by a consortium of researchers in a five-year (2013–2018) Coordinated Research Project (CRP) organized by the Joint Division of FAO/IAEA. The goal of this CRP was to elucidate tsetse-symbiome-pathogen molecular interactions to improve SIT and SIT-compatible interventions for trypanosomoses control by enhancing vector refractoriness. This would allow extension of SIT into areas with potential disease transmission. This paper highlights the CRP’s major achievements and discusses the science-based perspectives for successful mitigation or eradication of African trypanosomosis.     

Translocation and accumulation of translocate in the sugar beet petiole

Accumulation of translocate during steady-state labeling of photosynthate was measured in the source leaf petioles of sugar beet (Beta vulgaris L. monogerm hybrid). During an 8-hr period, 2.7% of the translocate or 0.38 μg carbon/min was accumulated per cm petiole. Material was stored mainly as sucrose and as compounds insoluble in 80% ethanol. The minimum peak velocity of translocation approached an average of 54 cm/hr as the specific activity of the ¹⁴CO₂ pulse was progressively increased. The ratio of cross sectional area required for translocation to actual sieve tube area in the petiole was 1.2. A regression analysis of translocation rate versus sieve tube cross sectional area yielded a coefficient of 0.76. The specific mass transfer rate in the petiole was 1.4 g/hr cm² phloem or 4.8 g/hr cm² sieve tube. Histoautoradiographic studies indicated that translocation occurs through the area of phloem occupied by sieve tubes and companion cells while storage occurs in these cells plus cambium and phloem parenchyma cells. The ability of the petiole to act as a sink for translocate is consistent with the concept that storage along path tissue serves to buffer sucrose concentration in the translocate during periods of fluctuating assimilation.     

Autökologische und saprobiologische Untersuchungen an Süsswasserciliaten

Zusammenfassung Von 31 häufig vorkommenden Süßwasserciliatenarten wurden in Form von Milieuspektren die ökologischen Potenzen gegenüber Temperatur, pH-Wert, 0₂, CO₂ (frei), NH₄, NH₃ (frei), H₂S und Gesamtsalzgehalt (für die beiden Typen: marines Brackwasser und binnenländischer Natronsee) zusammengestellt. Zur weiteren Kennzeichnung des Lebensraumes der einzelnen Ciliatenarten ist die Bakterienzahl (=Gesamtkeimzahl) angegeben.Soweit genügend Beobachtungsmaterial vorliegt, wurde außerdem der Optimalbereich des Vorkommens innerhalb der Gesamtspektren der aufgeführten Umweltfaktoren ermittelt.Die autökologischen Befunde werden jeweils verglichen mit der saprobiologischen Einstufung im Saprobiensystem der Wassergüte-beurteilung.

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Summary The ecological valencies (=limits of tolerance) of 31 species of freshwater ciliates with regard to the environmental factors temperature, pH, 0₂, free CO₂, NH₄, free NH₃, H₂S, and total salt content (brackish water and inland natron lake water) are tabulated. Furtheron the number of bacteria occurring together with the ciliates in question is presented.As far as possible from technical respects the range of optimum within the limits of tolerance is listed.The autecological results are compared with the indicator value of the particular species for the Saprobien System of monitoring water-quality.

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Aus dem Zoologischen Institut der Universität Bonn (Direktor: Prof. Dr. R. Danneel)

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Herrn Prof. Dr. H. Wurmbach zur Vollendung des 65. Lebensjahres am 28.3.1968 gewidmet.     

Zur Funktion des elektrischen Organs von Gnathonemus petersii (Gthr. 1862) (Mormyriformes,Teleostei)

Journal of Comparative Physiology A - In der vorliegenden Arbeit werden Untersuchungen an schwachelektrischen Fischen der Art Gnathonemus petersii (Günther 1862) beschrieben.     

Munc13-3 Is Required for the Developmental Localization of Ca2+ Channels to Active Zones and the Nanopositioning of Cav2.1 Near Release Sensors

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Conserved amino acids in the N- and C-terminal domains of integral membrane transporter FhuB define sites important for intra- and intermolecular interactions

Transport of iron(III) hydroxamates across the inner membrane of Escherichia coli is mediated by a periplasmic binding protein-dependent transport (PBT) mechanism. FhuB, the integral membrane component of the system, is composed of covalently linked halves (FhuB[N] and FhuB[C]) which still function when present as two distinct polypeptide chains. Our analysis of two uptake-deficient FhuB derivatives provides evidence for a mechanistically novel type of functional complementation:‘domain displacement’ in the cytoplasmic membrane. Amino acid residues 60 and 426 in the FhuB polypeptide chain may define key positions that are important for FhuB[N]–FhuB[C] interaction. Furthermore, FhuB derivatives, altered in either one of their conserved regions - typical of PBT related integral membrane proteins - displayed a dominant negative effect on ferric hydroxamate transport. The experimental data suggest that the two functionally equivalent conserved regions in FhuB[N] and FhuB[C] are primarily involved in the interaction with another component of the transport system, probably FhuC.     

Three-dimensional structures of photosynthetic reaction centers

In this article, the three-dimensional structures of photosynthetic reaction centers (RCs) are presented mainly on the basis of the X-ray crystal structures of the RCs from the purple bacteria Rhodopseudomonas (Rp.) viridis and Rhodobacter (Rb.) sphaeroides. In contrast to earlier comparisons and on the basis of the best-defined Rb. sphaeroides structure, a number of the reported differences between the structures cannot be confirmed. However, there are small conformational differences which might provide a basis for the explanation of observed spectral and functional discrepancies between the two species.A particular focus in this review is on the binding site of the secondary quinone (Q_B), where electron transfer is coupled to the uptake of protons from the cytoplasm. For the discussion of the Q_B site, a number of newlydetermined coordinate sets of Rp. viridis RCs modified at the Q_B site have been included. In addition, chains of ordered water molecules are found leading from the cytoplasm to the Q_B site in the best-defined structures of both Rp. viridis and Rb. sphaeroides RCs.Abbreviations B_A accessory bacteriochlorophyll in the active branch - B_B accessory bacteriochlorophyll in the inactive branch - D primary electron donor (special pair) - D_L special pair bacteriochorophyll bound by the L subunit - D_M special pair bacteriochorophyll bound by the M subunit - Q_A primary electron acceptor quinone - Q_B secondary electron acceptor quinone - RC reaction center - Rb. Rhodobacter - Rp. Rhodopseudomonas - _A bacteriopheophytin in the active branch - _B bacteriopheophytin in the inactive branch     

Rhizobium meliloti mutants deficient in phospholipid N-methyltransferase still contain phosphatidylcholine.

Phosphatidylcholine (PC) is the major membrane-forming phospholipid in eukaryotes. In addition to this structural function, PC is thought to play a major role in lipid turnover and signalling in eukaryotic systems. In prokaryotes, only some groups of bacteria, among them the members of the family Rhizobiaceae, contain PC. To understand the role of PC in bacteria, we have studied Rhizobium meliloti 1021, which is able to form nitrogen-fixing nodules on its legume host plants and therefore has a very complex phenotype. R. meliloti was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine, and potential mutants defective in phospholipid N-methyltransferase were screened by using a colony autoradiography procedure. Filters carrying lysed replicas of mutagenized colonies were incubated with S-adenosyl-L-[methyl-14C]methionine. Enzymatic transfer of methyl groups to phosphatidylethanolamine (PE) leads to the formation of PC and therefore to the incorporation of radiolabel into lipid material. Screening of 24,000 colonies for reduced incorporation of radiolabel into lipids led to the identification of seven mutants which have a much-reduced specific activity of phospholipid N-methyltransferase. In vivo labelling of mutant lipids with [14C]acetate showed that the methylated PC biosynthesis intermediates phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine are no longer detectable. This loss is combined with a corresponding increase in the potential methyl acceptor PE. These results indicate that PC biosynthesis via the methylation pathway is indeed blocked in the mutants isolated. However, mass spectrometric analysis of the lipids shows that PC was still present when the mutants had been grown on complex medium and that it was present in the mutants in wild-type amounts. In vivo labelling with [methyl-14C]methionine shows that in phospholipid N-methyltransferase-deficient mutants, the choline moiety of PC is not formed by methylation. These findings suggest the existence of a second pathway for PC biosynthesis in Rhizobium.     

Ligand-mediated metal-metal interactions in (ν:ν-fulvalene) bis (dicarbonylcobalt) and rhodium complexes

Gas phase photoelectron spectroscopy (PES) is used to investigate the bonding and electronic structure in (fv) [M(CO)₂]₂ (fv = fulvalene, η⁵:η⁵-C₁₀H₈²⁻; M = Co, Rh). The results for these bimetallic complexes are also compared to those for the analogous monometallic complexes CpM(CO)₂ (Cp = η⁵−C₅H₅⁻; M = Co, Rh) which have been reported previously. The low valence ionization patterns observed for CpCo(CO)₂ and (fv)[Co(CO)₂]₂ are very similar, indicating that there is little electronic interaction between the two metals of the dicobalt complex. The spectrum of (fv)[Rh(CO)₂]₂ also is very similar to the spectrum of CpRh(CO)₂, except that the first metal ionizations in the bimetallic rhodium compound show a significant splitting (0.45 eV). This splitting is due to electronic interaction between the two metal centers which occurs via communication through the fulvalene π system. The differences in electronic structure are compared to the differences in electrochemical behavior of the Co and Rh fulvalene complexes.