Restriction on Conjugational Transfer of pLS20 in Bacillus subtilis 168

Conjugational transfer of pLS20 in Bacillus subtilis Marburg 168 is restricted by the BsuM restriction-modification system. Restriction efficiency was measured using pLS20 derivatives possessing various numbers of XhoI sites, which are known to be recognized by BsuM. An increase in XhoI sites clearly reduced the conjugational efficiency of pLS20 as compared with that of pUB110 plasmid lacking XhoI.     

Transfer and expression of the cryIVB and cryIVD genes of Bacillus thuringiensis subsp. israelensis in Bacillus sphaericus 2297

Abstract The genes encoding the CryIVB and CryIVD crystal polypeptides of B. thuringiensis subsp. israelensis were cloned indepently on a stable shuttle vector, and transfered into B. sphaericus 2297. Recombinant cells expressed the B. thuringiensis toxins during sporulation and were shown to be toxic to Aedes aegypti fourth instar larvae, whereas the parental strain was not.     

Midsummer heat wave effects on lacustrine plankton: Variation of assemblage structure and fatty acid composition

The effects of the 2003 European heat wave on a freshwater plankton assemblage and its fatty acid (FA) composition were investigated. Composition and FA profiles of four size categories of planktonic organisms collected in 2003 were compared to those of the colder year 2002.     

Utilization of Serine, Leucine, Isoleucine, and Valine byThermoanaerobacter brockiiin the Presence of Thiosulfate orMethanobacteriumsp. as Electron Acceptors

Thermoanaerobacter brockiifermented serine to acetate and ethanol. It oxidized leucine to isovalerate, isoleucine to 2-methylbutyrate, and valine to isobutyrate only in the presence of thiosulfate, or when co-cultured withMethanobacteriumsp. This oxidative deamination was rendered thermodynamically possible by the ability ofT. brockiito reduce thiosulfate to sulfide or the transfer of reducing equivalents to the hydrogenotrophic methanogen. The results suggest thatT. brockiimay be of ecological significance in thermal environments in the turnover of amino acids, especially with thiosulfate or H₂-utilizing methanogens are present.     

Photosynthetic pigment concentration, organization and interconversions in a pale green Syrian landrace of barley (Hordeum vulgare L., Tadmor) adapted to harsh climatic conditions

Tadmor is a Syrian barley landrace that has adapted to semi-arid environments. Its leaves are pale green because of a 30% decrease in the chlorophyll and the carotenoid content of the chloroplasts (leading to a 7·5% decrease in light absorption) compared with barley genotypes that are not adapted to harsh Mediterranean climatic conditions (e.g. Plaisant). This difference in pigment content was attenuated during growth of the plants in strong light, but was strongly amplified when strong light was combined with a high growth temperature. The low pigment content of Tadmor leaves was not associated with significant changes in the pigment distribution between the photosystems or between the reaction centres of the photosystems and their associated chlorophyll antennae. No significant difference in the photosynthetic activity (O₂ production per unit absorbed light) was observed between Tadmor and Plaisant. The conversion of violaxanthin to zeaxanthin in strong light and its reversal in darkness were much faster and operated at a higher capacity in Tadmor leaves compared with Plaisant leaves, resulting in an increased photostability of photosystem II in the former leaves. The accelerated xanthophylls interconversion in the Syrian landrace was associated with, and possibly related to, an increased fluidity of the thylakoid membranes. The lipid peroxide level was lower in Tadmor compared with Plaisant. In contrast, no difference was found in the non-photochemical quenching of chlorophyll fluorescence between the two barley genotypes. The data indicate that the pale green Syrian landrace is equipped to survive excessive irradiance through a passive reduction of the light absorptance of its leaves, which mitigates the heating effects of strong light, and through the active protection of its photochemical apparatus by a rapid xanthophyll cycling.     

Atx1-like chaperones and their cognate P-type ATPases: copper-binding and transfer

Copper is an essential yet toxic metal ion. To satisfy cellular requirements, while, at the same time, minimizing toxicity, complex systems of copper trafficking have evolved in all cell types. The best conserved and most widely distributed of these involve Atx1-like chaperones and P_1B-type ATPase transporters. Here, we discuss current understanding of how these chaperones bind Cu(I) and transfer it to the Atx1-like N-terminal domains of their cognate transporter.     

Horizontal transfer of a mitochondrial plasmid

Direct evidence for horizontal transfer of a mitochodnrial plasmid from the discomyceteAscobolus immersus to the pyrenomycetePodospora anserina is presented. Southern blot hybridisation analysis, polymerase chain reaction (PCR) amplification, and DNA sequencing demonstrate transmission of a linear plasmid upon hyphal contact. DNA extraction from isolated organelles indicates a mitochondrial localisation for the plasmid inP. anserina. This is the first report of horizontal gene transfer among unrelated fungi. These results have important evolutionary implications for plasmid propagation in fungi.     

Low rates of iridoid glycoside hydrolysis in two Longitarsus leaf beetles with different feeding specialization confer tolerance to iridoid glycoside containing host plants

Iridoid glycosides are plant defence compounds that are deterrent and/or toxic for unadapted herbivores but are readily sequestered by dietary specialists of different insect orders. Hydrolysis of iridoid glycosides by β‐glucosidase leads to protein denaturation. Insect digestive β‐glucosidases thus have the potential to mediate plant–insect interactions. In the present study, mechanisms associated with iridoid glycoside tolerance are investigated in two closely‐related leaf beetle species (Coleoptera: Chrysomelidae) that feed on iridoid glycoside containing host plants. The polyphagous Longitarsus luridus Scopoli does not sequester iridoid glycosides, whereas the specialist Longitarsus tabidus Fabricius sequesters these compounds from its host plants. To study whether the biochemical properties of their β‐glucosidases correspond to the differences in feeding specialization, the number of β‐glucosidase isoforms and their kinetic properties are compared between the two beetle species. To examine the impact of iridoid glycosides on the β‐glucosidase activity of the generalist, L. luridus beetles are kept on host plants with or without iridoid glycosides. Furthermore, β‐glucosidase activities of both species are examined using an artificial β‐glucosidase substrate and the iridoid glycoside aucubin present in their host plants. Both species have one or two β‐glucosidases with different substrate affinities. Interestingly, host plant use does not influence the specific β‐glucosidase activities of the generalist. Both species hydrolyse aucubin with a much lower affinity than the standard substrate. The neutral pH reduces the β‐glucosidase activity of the specialist beetles by approximately 60% relative to its pH optimum. These low rates of aucubin hydrolysis suggest that the ability to sequester iridoid glycosides has evolved as a key to potentially preventing iridoid glycoside hydrolysis by plant‐derived β‐glucosidases.     

Effect of thiostrepton and 3′-terminal fragments of aminoacyl-tRNA on EF-Tu and ribosome-dependent GTP hydrolysis

The effect of the antibiotics thiostrepton and micrococcin on EF-T_u-catalyzed (ribosome-dependent) GTP hydrolysis in the presence of A-Phe, C-A-Phe, or C-C-A-Phe (related to the sequence of the 3′-terminus of aminoacyl-tRNA)(System I) or by methanol (‘uncoupled GTPase’, System II) was investigated. In System I, thiostrepton increases the binding affinities of the effectors to the EF-T_u·GTP·70 S ribosome complex, as well as the extent of the GTP hydrolysis, while the K^GTP_m is virtually unchanged. Similarly, in the uncoupled system (System II) and in the absence of effectors, thiostrepton significantly increases V^GTP_max, whereas K^GTP_m remains unaffected. Micrococcin is without any effect in both systems. The ‘uncoupled GTPase’ (in System II) is also strongly inhibited by C-A-Phe. The results indicate the crucial role of the EF-T_u site which binds the aminoacylated C-C-A terminus of aminoacyl-tRNA in promoting GTP hydrolysis. It follows that the binding of the model effectors (such as C-C-A-Phe) to that site is favorably influenced by the interaction of thiostrepton with the 50 S ribosomal subunit, whereas thiostrepton, per se, does not influence the affinity of EF-T_u for GTP.