Strange limits of stability in host-parasitoid systems

The classical Nicholson-Bailey model for a two species host-parasitoid system with discrete generations assumes random distributions of both hosts and parasitoids, randomly searching parasitoids, and random encounters between the individuals of the two species. Although unstable, this model induced many investigations into more complex host-parasitoid systems. Local linearized stability analysis shows that equilibria of host parasitoid systems within the framework of a generalized Nicholson-Bailey model are generally unstable. Stability is only possible if host fertility does not exceede ⁴=54.5982 and if superparasitism is unsuccessful. This special situation has already been discovered by Hassell et al. (1983) in their study of the effects of variable sex ratios on host parasitoid dynamics. We discuss global behaviour of the Hassell-Waage-May model using KAM-theory and illustrate its sensitivity to small perturbations, which can give rise to radically different patterns of the population dynamics of interacting hosts and parasitoids.     

Sex chromosome polymorphism and heterogametic males revealed by two cloned DNA probes in the ZW/ZZ fish Leporinus elongatus

In order to study the divergence of teleost sex chromosomes, subtractive cloning was carried out between genomic DNA of males and females of the rainbow trout (XX/XY) and of Leporinus elongatus (ZW/ZZ). Inserts cloned in a plasmid vector were individually tested on Southern blots of DNA of males and females for sex specificity. No sex-specific insert was obtained from trout, but two out of ten inserts cloned from L. elongatus showed sex-specific patterns in this species: one corresponds to a sequence present on both Z and W chromosomes, while the other is W specific. Sequences of these two inserts show neither clear homology with other known sequences, nor an open reading frame. They cross-hybridize with the genomic DNA of Leporinus friderici, but without sex-specific patterns. Twenty-four L. elongatus adults were sexed by gonadal observation, chromosomed examination and Southern hybridization with one or the other insert. Ten males and 11 females had chromosomes and hybridization patterns typical of their sex. One ZW female was recognized as a male with the W-specific probe. This was also the case for two unusual ZW males, one having a male hybridization pattern with the other probe. These three atypical individuals may result from single genetic exchanges between four regions of the Z and the W, giving rise to three atypical W chromosomes. Finding males with such atypical heterochromosomes in a female heterogametic species may indicate that a gradual transition occurs between the heterogametic systems.     

A phloem-specific sucrose-H+ symporter from Plantago major L. supports the model of apoplastic phloem loading

In this paper the cloning of a full-length cDNA clone encoding the PmSUC2 sucrose-H⁺ symporter from Plantago major is described. This plant allows the simple preparation of vascular bundles from the basal regions of fully developed source leaves and thus a separation of vascular and non-vascular tissue. A cDNA library was constructed from poly(A)⁺ RNA isolated from vascular bundles and used for the subsequent cloning of cDNAs. The respective mRNA is specifically expressed in the vascular bundles as shown on Northern blots of total RNA from vascular and non-vascular tissues. The PmSUC2 protein has 12 putative transmembrane helices and is highly homologous to other plant sucrose transporters. Substrate specificity and energy dependence of the transporter encoded by this cDNA were determined by expression in baker's yeast Saccharomyces cerevisiae. The PmSUC2 protein catalyses the transport of sucrose into transgenic yeast cells. Invertase null mutants of yeast expressing PmSUC2 accumulate sucrose more than 200-fold. This transport was sensitive to uncouplers or SH-group inhibitors. Plasma membranes from yeast cells expressing the PmSUC2 protein were purified and fused to proteoliposomes containing cytochrome-c-oxidase. In this system sucrose is accumulated only when proton motive force is generated, indicating that PmSUC2 is a sucrose-H⁺ symporter. The apparent molecular weight of the PmSUC2 protein is 35 kDa on 10% SDS-polyacrylamide gels. The presented data strongly support the theory of phloem loading from the apoplastic space by a sucrose-H⁺ symporter.     

16S rDNA sequence and phylogenetic position of an uncultivated spirochete from the hindgut of the termite Mastotermes darwiniensis Froggatt

Abstract We have analyzed the 16S rDNA sequence and the phylogenetic position of an uncultivated spirochete from the hindgut contents of the Australian termite Mastotermes darwiniensis Froggatt. The 16S rRNA genes of bacteria from the hindgut contents of Mastotermes darwiniensis were amplified by polymerase chain reaction. The amplification products were cloned and sequenced. The sequences were compared to known homologous primary structures. Two of the clones (MDS1 and MDS3) had an insert of 1498 nucleotides showing typical signatures of spirochete 16S rRNA sequences. The sequences of the two clones were most similar to the 16S rRNA sequence of Spirochaeta stenostrepta (89.8%) and Treponema sp. strain H1 (90.7%). Phylogenetical analysis positioned the hindgut spirochete sequence with that of the free-living anaerobic Spirochaeta stenostrepta and Treponema sp. strain H1 as its nearest relatives within the cluster of the spirochetes. We conclude that the analyzed SSU rDNA sequences originate from a spirochete related to the genus Treponema . It is possibly one of the uncultivated unique spirochetes symbiotic in termite hindguts.     

Turnover characteristics in continuous l-lysine fermentation

The turnover characteristics of a microbial bioreactor were comparatively investigated as a closed (batch) and a continuous stirred tank reactor (CSTR) open system, using a 2-l fermentor. Corynebacterium glutamicum (ATCC 21544) was chosen as the microorganism since it has the ability to produce l-lysine. Parameters measured were l-lysine production rates, glucose consumption rates and biomass production rates as a function of dilution rate, bioreactor volume and biomass concentration. The modes of microbial cell behaviour under steady-state and transition-state conditions were examined. Investigations on scaling properties of the CSTR system were also aimed at comparing scaling or allometry of metabolic rates in organisms that are also open energy dissipative systems.This investigation was first presented at the 10th Dechema-Jahrestagung der Biotechnologen, 1–3 June 1992, Karlsruhe, Germany     

Rotifer population dynamics in response to increased bacterial biomass and nutrients: a mesocosm experiment

The impact of organic nutrients and massive addition of bacteria was followed in lake water mesocosms in a eutrophic lake. Increased DOM initiated a sequence of trophic responses indicated by rapid increases in bacterioplankton, protozoa, and algal biomass. The populations of Keratella cochlearis and Keratella quadrata showed a distinct response by rapid increase in birth rate followed by maxima of production and abundance. This succession clearly reflected the trophic position of these rotifer populations in the food chain. A reverse response was observed in Conochilus unicornis.     

An SAR sequence containing 395 bp DNA fragment mediates enhanced,gene-dosage-correlated expression of a chimaeric heat shock gene in transgenic tobacco plants

A 395 bp fragment located downstream from the soybean heat shock geneGmhsp 17.6-L exhibits several characteristics of scaffold attachment region (SAR) sequences. It contains matrix consensus elements, a topoisomerase II binding sequence and it associates with the isolated nuclear scaffold of soybeanin vitro. Chimaeric genes containing the SAR_L fragment either at one side (5 or 3) or at both sides of a heat shock promoter-regulated -glucuronidase reporter gene were constructed. A five-to nine-fold increase of heat-inducible -glucuronidase activity was observed in transgenic tobacco plants containing constructs with SAR_L fragments either at both sides or with at least one SAR_L copy located upstream from the reporter gene. The gene copy number is positively correlated with the level of heat-inducible reporter gene activity in these. plants but positional effects are not entirely eliminated. Thus, SAR sequences may potentially be used to increase gene expression, via as yet unknown mechanisms, and to reduce adverse effects on the expression of multiple gene copies in transgenic plants.     

Characterization of a quail suspension cell line for production of a fusogenic oncolytic virus

The development of efficient processes for the production of oncolytic viruses (OV) plays a crucial role regarding the clinical success of virotherapy. Although many different OV platforms are currently under investigation, manufacturing of such viruses still mainly relies on static adherent cell cultures, which bear many challenges, particularly for fusogenic OVs. Availability of GMP-compliant continuous cell lines is limited, further complicating the development of commercially viable products. BHK21, AGE1. CR and HEK293 cells were previously identified as possible cell substrates for the recombinant vesicular stomatitis virus (rVSV)-based fusogenic OV, rVSV-NDV. Now, another promising cell substrate was identified, the CCX.E10 cell line, developed by Nuvonis Technologies. This suspension cell line is considered non-GMO as no foreign genes or viral sequences were used for its development. The CCX.E10 cells were thus thoroughly investigated as a potential candidate for OV production. Cell growth in the chemically defined medium in suspension resulted in concentrations up to 8.9 × 10⁶ cells/mL with a doubling time of 26.6 h in batch mode. Cultivation and production of rVSV-NDV, was demonstrated successfully for various cultivation systems (ambr15, shake flask, stirred tank reactor, and orbitally shaken bioreactor) at vessel scales ranging from 15 mL to 10 L. High infectious virus titers of up to 4.2 × 10⁸ TCID₅₀/mL were reached in orbitally shaken bioreactors and stirred tank reactors in batch mode, respectively. Our results suggest that CCX.E10 cells are a very promising option for industrial production of OVs, particularly for fusogenic VSV-based constructs.     

Circannual Variations in Blood Cholesterol Levels

The seasonality of blood cholesterol is still not well established. Some have described a seasonal pattern with highest levels during autumn and lowest in summer, whereas others have reported no change. A number of studies showed circannual variations with maximum levels in winter and minimum in summer. The aim of this study was to examine the circannual variation of cholesterol in a large cohort in Israel. In the Israeli CORDIS study, employees of 21 factories were screened for cardiovascular disease risk factors during 1985-7. As part of the information gathered, serum cholesterol and blood counts were available for 3,726 men and 1,514 women. Serum cholesterol levels fit a circannual rhythm assessed by the cosinor analysis. Highest levels of serum cholesterol were found in spring and lowest in summer. We conclude that there is a circannual change of serum cholesterol, which could be partially associated with changes in environmental temperature. The circannual variation in serum cholesterol was considerable and should be taken into account when carrying out clinical evaluation of patients.