Mutants of bacteriophage T7 that escape F restriction

Mutants of bacteriophage T7 that escape F restriction have been isolated. Two mutations in gene 10, which codes for the capsid protein, and one mutation in gene 1.2 are required for these phages to grow on F-containing strains. The products of these two genes are the two targets of the exclusion system; the presence of either wild-type product results in an abortive infection. Phages that grow normally in male hosts still lead to membrane dysfunction and nucleotide efflux from the infected cell. This type of membrane damage and the abortive infection are therefore separable phenomena.     

Body size and host range in European Heteroptera

We used data on body size and host range of phytophagous Heteroptera in central Europe, an inverse measure of specialisation, to analyse the relationship of body size vs specialisation: 1) we found a clear positive relationship between body size and host range using species as independent data points. 2) However, a nested analysis of variance shows that most of the variance in body size occurred at higher taxonomic levels whereas most of the variance in host specialisation occurred between species. This suggests different phylogenetic inertia of body size and specialisation. Nevertheless, using means of different higher taxonomic levels there is still a significant positive correlation between body size and host range. 3) With more sophisticated methods of correcting for the phylogenetic relatedness between species, the positive correlation between body size and host range still holds, despite the different assumptions of each method. Thus, the relationship between body size and host range is a very robust pattern in true bugs.     

Insights into the Mechanism of Ligand Binding to Octopine Dehydrogenase from Pecten maximus by NMR and Crystallography

Octopine dehydrogenase (OcDH) from the adductor muscle of the great scallop, Pecten maximus, catalyzes the NADH dependent, reductive condensation of L-arginine and pyruvate to octopine, NAD⁺, and water during escape swimming and/or subsequent recovery. The structure of OcDH was recently solved and a reaction mechanism was proposed which implied an ordered binding of NADH, L-arginine and finally pyruvate. Here, the order of substrate binding as well as the underlying conformational changes were investigated by NMR confirming the model derived from the crystal structures. Furthermore, the crystal structure of the OcDH/NADH/agmatine complex was determined which suggests a key role of the side chain of L-arginine in protein cataylsis. Thus, the order of substrate binding to OcDH as well as the molecular signals involved in octopine formation can now be described in molecular detail.     

Global dung webs: high trophic generalism of dung beetles along the latitudinal diversity gradient

At the global scale, species diversity is known to strongly increase towards the equator for most taxa. According to theory, a higher resource specificity of consumers facilitates the coexistence of a larger number of species and has been suggested as an explanation for the latitudinal diversity gradient. However, only few studies support the predicted increase in specialisation or even showed opposite results. Surprisingly, analyses for detritivores are still missing. Therefore, we performed an analysis on the degree of trophic specialisation of dung beetles. We summarised 45 studies, covering the resource preferences of a total of 994503 individuals, to calculate the dung specificity in each study region. Our results highlighted a significant (4.3‐fold) increase in the diversity of beetles attracted to vertebrate dung towards the equator. However, their resource specificity was low, unrelated to diversity and revealed a highly generalistic use of dung resources that remained similar along the latitudinal gradient.     

Diacetyl and acetoin production from the co-metabolism of citrate and xylose by Leuconostoc mesenteroides subsp. mesenteroides

The co-metabolism of citrate plus xylose by Leuconostoc mesenteroides subsp. mesenteroides results in a growth stimulation, an increase in d-lactate and acetate production and repression of ethanol production. This correlated well with the levels of key enzymes involved. A partial repression of alcohol dehydrogenase and a marked stimulation of acetate kinase were observed. High citrate bioconversion yields in diacetyl plus acetoin were obtained at pH 5.2 in batch (11.5%) or in chemostat (up to 17.4%) culture. In contrast, no diacetyl or acetoin was detected in citrate plus glucose fermentation. Received: 6 December 1996 / Received revision: 14 February 1997 / Accepted: 14 February 1997     

beta]-1,3-Glucanase Is Cryoprotective in Vitro and Is Accumulated in Leaves during Cold Acclimation

We have used isolated spinach (Spinacea oleracea L.) thylakoid membranes to investigate the possible cryoprotective properties of class I [beta]-1,3-glucanase (1,3-[beta]-D-glucan 3-glucanohydrolase; EC 3.2.1.39) and chitinase. Class I [beta]-1,3-glucanase that was purified from tobacco (Nicotiana tabacum L.) protected thylakoids against freeze-thaw injury in our in vitro assays, whereas class I chitinase from tobacco had no effect under the same conditions. The [beta]-1,3-glucanase acted by reducing the influx of solutes into the membrane vesicles during freezing and thereby reduced osmotic stress and vesicle rupture during thawing. Western blots probed with antibodies directed against tobacco class I [beta]-1,3-glucanase showed that in spinach and cabbage (Brassica oleracea L.) leaves an isoform of 41 kD was accumulated during frost hardening under natural conditions.