Identification of OmpT as the Protease That Hydrolyzes the Antimicrobial Peptide Protamine before It Enters Growing Cells of Escherichia coli

The influence of extracytoplasmic proteases on the resistance of Escherichia coli to the antimicrobial peptide protamine was investigated by testing strains with deletions in the protease genes degP, ptr, and ompT. Only ΔompT strains were hypersusceptible to protamine. This effect was abolished by plasmids carrying ompT. Both at low and at high Mg²⁺ concentrations, ompT⁺ strains cleared protamine from the medium within a few minutes. By contrast, at high Mg²⁺ concentrations, protamine remained present for at least 1 h in the medium of an ompT strain. These data indicate that OmpT is the protease that degrades protamine and that it exerts this function at the external face of the outer membrane.     

KtrAB, a New Type of Bacterial K+-Uptake System from Vibrio alginolyticus

Vibrio alginolyticus contained two adjacent genes, ktrA and ktrB, which encode a new type of bacterial K⁺-uptake system. KtrA and KtrB are peripheral and integral membrane proteins, respectively. Six of the nine sequenced bacterial genomes contain homologs to both ktrA and ktrB, suggesting that KtrAB is widespread.     

Ecological correlates of seed persistence in soil in the north-west European flora

1 Using the data in a recently published seed bank database for north-west Europe, we describe how a species' seed bank behaviour can be characterized by a single 'longevity index', and investigate how representative the information in the database is of the north-west European flora. We also test the hypotheses that seeds of short-lived species are more persistent than those of long-lived species, and long-lived seeds are characteristic of species living in disturbed habitats.
2 The data are not representative of the north-west European flora as a whole; they are a fair reflection of a research effort that has been largely directed towards grassland and arable weeds. Data for rare species, non-agricultural habitats in general and wetlands, rocky habitats and native woodland in particular, are scarce or absent.
3 Annuals and biennials almost always have more persistent seeds than related perennials, and this difference is most striking when, as in Anagallis arvensis and Aphanes arvensis , the short-lived species have moved well away from the 'core' habitat of the family. Confamilial monocarps and polycarps do not differ consistently in seed mass.
4 Gradients of habitat disturbance are accompanied by predictable changes in seed persistence, which are themselves often (but not always) accompanied by parallel shifts in seed size. These results suggest that increasing habitat disturbance (i.e. increasing density-independent mortality) always selects for increased seed persistence, confirming both theory and previous analyses. However, increased seed persistence is not always associated with reduced seed size. This is because persistence depends not only on seed size, but on other traits, many of them physiological. In many habitats the probability of seed burial is strongly linked to seed size and shape, but in arable habitats cultural practices have broken this link.     

Soil nutrient input effects on seed longevity: a burial experiment with fen-meadow species

1. Effects of high nutrient input on the longevity and viability of buried seed are examined. Seeds of 17 fen-meadow species were buried in nylon mesh bags at four sites in the Netherlands and one site in Great Britain in plots to which N, P, K fertilizers are applied. Prior to burial germination tests were conducted on the seeds of each species. This paper describes the results of the viability tests on the seeds that were exhumed after one and 2 years of burial.
2. The percentage of seeds that germinated after 1 year of burial was significantly lower than the pre-burial percentage for the majority of the species. After 2 years of burial the germination percentage further decreased. A few species, such as the Carex species, did, however, show an increase in germination percentage indicating that the burial conditions allowed dormancy controls to be broken.
3. Differences in the edaphic conditions between the sites appeared to affect germination percentages after 1 year of burial. A difference in germination response between sites was observed for Carex acutiformis, Filipendula ulmaria and Lychnis flos-cuculi .
4. A significantly higher germination percentage was found at the Great Britain site for F. ulmaria in the phosphate treatment compared with the potassium treatment and the control after 1 year of burial. In contrast to many literature assessments no significant effects of fertilizer application was found after 2 years.
5. For all sites, except one in the Netherlands, the total number of seeds that germinated was lower in 1996 than in 1995.     

Evolution of Syncytium-Inducing and Non-Syncytium-Inducing Biological Virus Clones in Relation to Replication Kinetics during the Course of Human Immunodeficiency Virus Type 1 Infection

To investigate the temporal relationship between human immunodeficiency virus type 1 (HIV-1) replicative capacity and syncytium-inducing (SI) phenotype, biological and genetic characteristics of longitudinally obtained virus clones from two HIV-1-infected individuals who developed SI variants were studied. In one individual, the emergence of rapidly replicating SI and non-syncytium-inducing (NSI) variants was accompanied by a loss of the slowly replicating NSI variants. In the other subject, NSI variants were always slowly replicating, while the coexisting SI variants showed an increase in the rate of replication. Irrespective their replicative capacity, the NSI variants remained present throughout the infection in both individuals. Phylogenetic analysis of the V3 region showed early branching of the SI variants from the NSI tree. Successful SI conversion seemed a unique event since no SI variants were found among later-stage NSI variants. This was also confirmed by the increasing evolutionary distance between the two subpopulations. At any time point during the course of the infection, the variation within the coexisting SI and NSI populations did not exceed 2%, indicating continuous competition within each viral subpopulation.     

Effect of pseudobactin 358 production by Pseudomonas putida WCS358 on suppression of fusarium wilt of carnations by nonpathogenic Fusarium oxysporum Fo47.

Nonpathogenic Fusarium oxysporum Fo47b10 combined with Pseudomonas putida WCS358 efficiently suppressed fusarium wilt of carnations grown in soilless culture. This suppression was significantly higher than that obtained by inoculation of either antagonistic microorganism alone. The increased suppression obtained by Fo47b10 combined with WCS358 only occurred when Fo47b10 was introduced at a density high enough (at least 10 times higher than that of the pathogen) to be efficient on its own. P. putida WCS358 had no effect on disease severity when inoculated on its own but significantly improved the control achieved with nonpathogenic F. oxysporum Fo47b10. In contrast, a siderophore-negative mutant of WCS358 had no effect on disease severity even in the presence of Fo47b10. Since the densities of both bacterial strains at the root level were similar, the difference between the wild-type WCS358 and the siderophore-negative mutant with regard to the control of fusarium wilt was related to the production of pseudobactin 358. The production of pseudobactin 358 appeared to be responsible for the increased suppression by Fo47b10 combined with WCS358 relative to that with Fo47b10 alone.     

Long-term changes of salt marsh communities by cattle grazing

Over a period of 9 years a grazing experiment was carried out in the mainland salt marsh of the Leybucht (Niedersachsen) with three stocking rates, namely, 0.5 ha^-1, 1 ha^-1, and 2 cattle ha^-1. These were also compared with an abandoned area. The results are based on sampling of the invertebrates in 1980, 1981, 1982, and 1988, and of the vegetation in 1980 and 1988. The rate of sedimentation is highest in the Puccinellia maritima-zone and decreases with the increase of stocking rates. The Elymus pycnanthus vegetation type becomes dominant in the higher salt marsh in the abandoned site. The canopy height decreases with increasing stocking rate, whereas a gradient in the structure of the vegetation develops with the lowest stocking rate. The population densities, the species-richness and the community diversity of invertebrates increases after the cessation of grazing. The high rate of sedimentation in the abandoned site promotes the immigration of species from higher salt marsh levels and adjacent grasslands, and eventually halotopophilous species and communities may disappear. On the other hand grazing reduces numerous species living both in or on upper parts of the vegetation or being sensitive to trampling by cattle. The community structure shows that the salt marsh ecosystem changed from a food web dominated by plant feeding animals to a food web dominated by animals foraging on detritus. The salt marsh management has to be differentiated into both ungrazed and lightly grazed areas (each 50%) or an overall grazing in large areas with less than 0.5 cattle ha^-1.     

New polymorphic DNA marker close to the fragile site FRAXA

DNA from a human-hamster hybrid cell line, 908-K1B17, containing a small terminal portion of the long arm of the human X chromosome as well as the pericentric region of 19q was used as starting material for the isolation of an X-chromosome-specific DNA segment, RN1 (DXS369), which identifies a XmnI RFLP. Linkage analysis in fragile X families resulted in a maximum lod score of 15.3 at a recombination fraction of 0.05 between RN1 and fra(X). Analysis of recombinations around the fra(X) and distal to DXS105. Analysis of the marker content of hybrid cell line 908K1B17 suggests the localization of RN1 between DXS98 and fra(X). Heterozygosity of DXS369 is approximately 50%, which extends the diagnostic potential of RFLP analysis in fragile X families significantly.