Involvement of a phospholipase C in the hemolytic activity of a clinical strain of <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis>

Background  

Pseudomonas fluorescens is a ubiquitous Gram-negative bacterium frequently encountered in hospitals as a contaminant of injectable material and surfaces. This psychrotrophic bacterium, commonly described as unable to grow at temperatures above 32°C, is now considered non pathogenic. We studied a recently identified clinical strain of P. fluorescens biovar I, MFN1032, which is considered to cause human lung infection and can grow at 37°C in laboratory conditions.     

Colonisation and mass rearing: learning from others

Mosquitoes, just as other insects produced for the sterile insect technique (SIT), are subjected to several unnatural processes including laboratory colonisation and large-scale factory production. After these processes, sterile male mosquitoes must perform the natural task of locating and mating with wild females. Therefore, the colonisation and production processes must preserve characters necessary for these functions. Fortunately, in contrast to natural selection which favours a suite of characteristics that improve overall fitness, colonisation and production practices for SIT strive to maximize only the few qualities that are necessary to effectively control populations.However, there is considerable uncertainty about some of the appropriate characteristics due to the lack of data. Development of biological products for other applications suggest that it is possible to identify and modify competitiveness characteristics in order to produce competitive mass produced sterile mosquitoes. This goal has been pursued - and sometimes achieved - by mosquito colonisation, production, and studies that have linked these characteristics to field performance. Parallels are drawn to studies in other insect SIT programmes and aquaculture which serve as vital technical reference points for mass-production of mosquitoes, most of whose development occurs - and characteristics of which are determined - in an aquatic environment. Poorly understood areas that require further study are numerous: diet, mass handling and genetic and physiological factors that influence mating competitiveness. Compromises in such traits due to demands to increase numbers or reduce costs, should be carefully considered in light of the desired field performance.     

AB5 toxins: structures and inhibitor design

High-resolution crystal structures of AB₅ toxins in their native form or in complex with a variety of ligands have led to the structure-based design and discovery of inhibitors targeting different areas of the toxins. The most significant progress is the development of highly potent multivalent ligands that block binding of the toxins to their receptors.     

The small-subunit ribosomal RNA gene sequences from the hypotrichous ciliates Oxytricha nova and Stylonychia pustulata

We have determined the complete nucleotide sequence of the small- subunit ribosomal RNA genes for the ciliate protozoans Stylonychia pustulata and Oxytricha nova. The sequences are homologous and sufficiently similar that these organisms must be closely related. In a phylogeny inferred from comparisons of several eukaryotic small-subunit ribosomal RNAs, the divergence of the ciliates from the eukaryotic line of descent is seen to coincide with the radiation of the plants, the animals, and the fungi. This radiation is preceded by the divergence of the slime mold, Dictyostelium discoideum.      

Population dynamics ofDaphnia rosea in a small eutrophic pond

The population dynamics ofDaphnia rosea were studied in a small, eutrophic fish-free pond during November 1986–November 1987.D. rosea showed two density peaks in 1987, a high peak in spring and a slightly lower one in autumn, but they disappeared in mid- and late summer when a smaller cladoceran,Ceriodaphnia reticulata, dominated. The rapid decline in density ofD. rosea in mid-May and the low density in June/July were preceded by or coincided with a period of increased male density, the appearance of ephippial females, smaller body length of adult females, decreased brood size, and increased frequency of empty brood chambers, all of which indicate a worsening food situation. The rapid density decline ofD. rosea in mid-May was considered attributable neither to increasing water temperature, nor predation by the dipteranChaoborus flavicans, but to insufficient food conditions for the maintenance of stable reproduction. Although edible phytoplankton was abundant in June/July, the general food situation was not suitable forD. rosea due to blooms of the large-celled dinoflagellate,Ceratium hirundinella, which probably inhibited the feeding activity ofD. rosea. TheC. hirundinella blooms might also be important for the shift of the dominant herbivore from the largerD. rosea to the smallerCeriodaphnia reticulata in August/September.     

Adverse environmental conditions influence age-related innate immune responsiveness

Background-  

The innate immune system plays an important role in the recognition and induction of protective responses against infectious pathogens, whilst there is increasing evidence for a role in mediating chronic inflammatory diseases at older age. Despite indications that environmental conditions can influence the senescence process of the adaptive immune system, it is not known whether the same holds true for the innate immune system. Therefore we studied whether age-related innate immune responses are similar or differ between populations living under very diverse environmental conditions.     

Ecologists can enable communities to implement malaria vector control in Africa

Background

Malaria imposes significant costs on households and the poor are disproportionately affected. However, cost data are often from quantitative surveys with a fixed recall period. They do not capture costs that unfold slowly over time, or seasonal variations. Few studies investigate the different pathways through which malaria contributes towards poverty. In this paper, a framework indicating the complex links between malaria, poverty and vulnerability at the household level is developed and applied using data from rural Kenya.

Methods

Cross-sectional surveys in a wet and dry season provide data on treatment-seeking, cost-burdens and coping strategies (n = 294 and n = 285 households respectively). 15 case study households purposively selected from the survey and followed for one year provide in-depth qualitative information on the links between malaria, vulnerability and poverty.

Results

Mean direct cost burdens were 7.1% and 5.9% of total household expenditure in the wet and dry seasons respectively. Case study data revealed no clear relationship between cost burdens and vulnerability status at the end of the year. Most important was household vulnerability status at the outset. Households reporting major malaria episodes and other shocks prior to the study descended further into poverty over the year. Wealthier households were better able to cope.

Conclusion

The impacts of malaria on household economic status unfold slowly over time. Coping strategies adopted can have negative implications, influencing household ability to withstand malaria and other contingencies in future. To protect the poor and vulnerable, malaria control policies need to be integrated into development and poverty reduction programmes.     

Free brownian motion of individual lipid molecules in biomembranes

The mobility of phospolipids in free-standing and supported membranes was investigated on the level of individual molecules. For the analysis of trajectories a new statistical treatment was developed that permitted us to clearly distinguish different types of diffusional motion. A freely diffusing subfraction of lipids within supported membranes was identified. Its mobility was characterized by a mean lateral diffusion constant of D(supp) = 4.6 &mgr;m(2)/s. In comparison, the mobility of lipids embedded in "free-standing" planar membranes yielded an increase in the mean diffusion constant by a factor of 4.5, D(free) = 20.6 &mgr;m(2)/s. This increase is attributed to the ultrathin (</=1 nm) lubricating water layer between membranes and glass support.     

Phylogeny of the genus trichoderma based on sequence analysis of the internal transcribed spacer region 1 of the rDNA cluster

Sequences of the internal transcribed spacer region 1 (ITS1) of the ribosomal DNA were used to determine the phylogenetic relationships of species of Trichoderma sect. Pachybasium. To this end, 85 strains-including all the available ex-type strains-were analyzed. Parsimony analysis demonstrated that the section is nonmonophyletic, distributing the 85 strains among three main groups that were supported by bootstrap values. Group A comprises two clades (A1 and A2), with A1 including T. polysporum, T. piluliferum, and T. minutisporum, while A2 included T. hamatum, T. pubescens, and T. strigosum in addition to species previously included in sect. Trichoderma (i.e., T. viride, T. atroviride, and T. koningii). The ex-type strain of T. fasciculatum formed a separate branch basal to clade A. Clade B contained the sect. Pachybasium members T. harzianum, T. fertile, T. croceum, T. longipile, T. strictipile, T. tomentosum, T. oblongisporum, T. flavofuscum, T. spirale, and the anamorphs of Hypocrea semiorbis and H. cf. gelatinosa. Sequence differences among clades A1, A2, and B were in the same order of magnitude as between each of them and T. longibrachiatum, which was used as an outgroup in these analyses. Sequence differences within clades A1, A2, and B were considerably smaller: in some cases (i.e., T. virens and T. flavofuscum; T. strictipile and H. cf. gelatinosa), the ITS1-sequences were identical, suggesting conspecifity. In other cases (e.g., T. crassum and T. longipile; T. harzianum, T. inhamatum, T. croceum, T. fertile, and H. semiorbis; T. hamatum and T. pubescens; and T. viride, T. atroviride, and T. koningii) differences were in the range of 1-3 nt only, suggesting a very close phylogenetic relationship. The sequence of a previously described aggressive mushroom competitor group of T. harzianum strains (Th2) was strikingly different from that of the ex-type strain of T. harzianum and closely related species and is likely to be a separate species. Copyright 1998 Academic Press.     

Two-dimensional NMR studies and secondary structure of cobrotoxin in aqueous solution

The 1H-NMR spectra of cobrotoxin, a neurotoxic protein isolated from Formosan cobra Naja naja atra, have been studied by two-dimensional NMR techniques. Of 62 amino acid residues in cobrotoxin, the complete assignments of 58 residues have been made. The resonances from several of the remaining residues have been identified but not yet specifically assigned. The secondary structure of an antiparallel triple- and double-stranded beta-sheet has also been determined by observing the NOE.