Competition between native and monoacetylated polymyxin for charged adsorption sites

The native antibiotic polymyxin B, carrying five positive charges, displaces the monoacetylated on from its adsorbed state at the interface between negatively charged lipid layers ans water. A simulation model for asdorption, governed by electrostatic forces, is presented. The model adequently representes the competitive adsorption kinetics and equilibria.     

Molecular taxonomy and phylogenetic position of lactic acid bacteria

Lactic acid bacteria, important in food technology, are Gram-positive organisms exhibiting a DNA G + C content of less than 50 mol%. Phylogenetically they are members of the Clostridium-Bacillus subdivision of Gram-positive eubacteria. Lactobacillus and streptococci together with related facultatively anaerobic taxa evolved as individual lines of descent about 1.5-2 billion years ago when the earth passed from an anaerobic to an aerobic environment. In contrast to the traditional, morphology-based classification, the genus Lactobacillus is intermixed with strains of Pediococcus and Leuconostoc. Similarly, the physiology-based clustering of lactobacilli into Thermo-, Strepto- and Betabacterium does not agree with their phylogenetic relationships. On the other hand, the phenotypically defined genus Streptococcus is not a phylogenetic coherent genus but its members fall into at least 3 moderately related genera, i.e. Streptococcus, Lactococcus and Enterococcus. The genus Bifidobacterium, frequently grouped with the lactobacilli, is the most ancient group of the second, the Actinomycetes subdivision of the Gram-positive eubacteria. In addition, propionibacteria, microbacteria and brevibacteria belong to this subdivision but the latter organisms appear as offshoots of non-lactic acid bacteria.     

Bacteriophage receptors of Lactococcus lactis subsp. 'diacetylactis' F7/2 and Lactococcus lactis subsp. cremoris Wg2-1

Bacteriophage P008 revealed irreversible and uniform adsorption to cell walls of L. lactis subsp. 'diacetylactis' F7/2, whereas phage P127 adsorbed reversibly to a limited number of receptor sites on cell walls of L. lactis subsp. cremoris Wg2-1. Neither extraction of lipids, cell wall- and membrane-teichoic acids nor enzymatic degradation of proteins altered the binding efficiencies of both cell wall fractions. However, phage binding was inhibited, when cell walls were subjected to lysozyme, metaperiodate, or acid treatments. This reflects that a carbohydrate component embedded in the peptidoglycan matrix is part of the phage receptors of strains F7/2 and Wg2-1.     

Differential accumulation of the transcripts of 22 novel protein kinase genes in Arabidopsis thaliana

22 novel members of the Arabidopsis thaliana protein kinase family (AKs) were identified by using degenerate oligonucleotide primers directed to highly conserved amino acid sequences of the protein kinase (PK) catalytic domain. Of these 22 genes, 16 turned out to carry intron sequences. Homologies of AK sequences were detected to S-locus receptor protein kinases (SRKs) from Brassica spp., to SRK-like PKs from maize and A. thaliana and to several other receptor PKs from A. thaliana. Sequence similarity was also detected to Ca²⁺-dependent PKs (CDPKs) from rape and soybean, to SNF1 and to CDC2 homologues. The genomic organization and the accumulation of the mRNAs from these 22 AK genes were investigated.     

Effect of polymyxin B on the structure and the stability of lipid layers

Summary Polymyxin B (PX) does not penetrate phospholipid monolayers and bilayers at low field strength across the lipid layers. The degree of penetration of PX is evaluated from its effect on the capacitance of the monolayers and on the conductance of the bilayers. PX added to one side of a bilayer causes its destabilization, it also enhances destabilization of lipid monolayers at positive electric fields across the surface layer in the direction of the adsorbed PX. PX lowers very little the fluorescence polarization of 1,6-diphenyl 1,3,5 hexatriene embedded in phospholipid vesicles. It is suggested that the penetration mechanism of PX into gram-negative bacteria is based on transient local breakdown of the plasma membrane.     

Differential fluorescence labelling with 5-dimethyl-aminonaphthalene-1-sulfonyl chloride of intact cells and isolated membranes in Salmonella typhimurium and Acholeplasma laidlawii

For fluorescence labelling intact cells and isolated cell envelopes (membranes) from Salmonella typhimurium and Acholeplasma laidlawii were treated with mixed dansylchloride-lecithin-cholesterol vesicles. This kind of dansylation, which has been supposed to be specific for cell surface proteins, produced fluorescent protein pattern after SDS-polyacrylamide gel electrophoresis only when isolated envelopes were dansylated. Acid hydrolysis of fluorescent cell envelopes of Salmonella typhimurium yielded O-dansyltryosine and epsilon-N-dansyl-lysine besides the free sulfonic acid and unidentified compounds. However, no fluorescent proteins were detectable in cell envelopes isolated from dansylated intact bacteria from Salmonella typhimurium. In accord Acholeplasma laidlawii showed only fluorescence from proteins with a molecular weight higher than 100000.     

Phylogenetic position of Gluconobacter species as a coherent cluster separated from all Acetobacter species on the basis of 16S ribosomal RNA sequences

Abstract The 16S rRNA sequences from the Gluconobacter species G. asaii G. cerinus and G. frateurii were determined and compared with homologous sequences from published databases and sequences of G. oxydans and Acetobacter species previously described [Sievers M., Ludwig W. and Teuber M. (1994) System. Appl. Microbiol. 17, 189–196]. The Gluconobacter species have unique 16S rRNA sequences and exhibit sequence similarity values of 97.4 to 99.1%, corresponding to 36 to 14 base differences. The phylogenetic tree inferring methods (distance matrix, maximum parsimony and maximum likelihood) show that the species of Gluconobacter form a coherent, closely related cluster. Based on the distance matrix method including Rhodopila globiformis as an outgroup reference organism, Gluconobacter is well separated from Acetobacter .     

Distribution and Ecophysiology of Calanoid Copepods in Relation to the Oxygen Minimum Zone in the Eastern Tropical Atlantic

Oxygen minimum zones (OMZs) affect distribution patterns, community structure and metabolic processes of marine organisms. Due to the prominent role of zooplankton, especially copepods, in the marine carbon cycle and the predicted intensification and expansion of OMZs, it is essential to understand the effects of hypoxia on zooplankton distribution and ecophysiology. For this study, calanoid copepods were sampled from different depths (0–1800 m) at eight stations in the eastern tropical Atlantic (3°47′N to 18°S) during three expeditions in 2010 and 2011. Their horizontal and vertical distribution was determined and related to the extent and intensity of the OMZ, which increased from north to south with minimum O₂ concentrations (12.7 µmol kg⁻¹) in the southern Angola Gyre. Calanoid copepod abundance was highest in the northeastern Angola Basin and decreased towards equatorial regions as well as with increasing depth. Maximum copepod biodiversity was observed in the deep waters of the central Angola Basin. Respiration rates and enzyme activities were measured to reveal species-specific physiological adaptations. Enzyme activities of the electron transport system (ETS) and lactate dehydrogenase (LDH) served as proxies for aerobic and anaerobic metabolic activity, respectively. Mass-specific respiration rates and ETS activities decreased with depth of occurrence, consistent with vertical changes in copepod body mass and ambient temperature. Copepods of the families Eucalanidae and Metridinidae dominated within the OMZ. Several of these species showed adaptive characteristics such as lower metabolic rates, additional anaerobic activity and diel vertical migration that enable them to successfully inhabit hypoxic zones.     

Differential expression of interferon responsive genes in rodent models of transmissible spongiform encephalopathy disease

Background

Alzheimer's disease (AD) is characterized by a decline in cognitive function and accumulation of amyloid-β peptide (Aβ) in extracellular plaques. Mutations in amyloid precursor protein (APP) and presenilins alter APP metabolism resulting in accumulation of Aβ42, a peptide essential for the formation of amyloid deposits and proposed to initiate the cascade leading to AD. However, the role of Aβ40, the more prevalent Aβ peptide secreted by cells and a major component of cerebral Aβ deposits, is less clear. In this study, virally-mediated gene transfer was used to selectively increase hippocampal levels of human Aβ42 and Aβ40 in adult Wistar rats, allowing examination of the contribution of each to the cognitive deficits and pathology seen in AD.

Results

Adeno-associated viral (AAV) vectors encoding BRI-Aβ cDNAs were generated resulting in high-level hippocampal expression and secretion of the specific encoded Aβ peptide. As a comparison the effect of AAV-mediated overexpression of APPsw was also examined. Animals were tested for development of learning and memory deficits (open field, Morris water maze, passive avoidance, novel object recognition) three months after infusion of AAV. A range of impairments was found, with the most pronounced deficits observed in animals co-injected with both AAV-BRI-Aβ40 and AAV-BRI-Aβ42. Brain tissue was analyzed by ELISA and immunohistochemistry to quantify levels of detergent soluble and insoluble Aβ peptides. BRI-Aβ42 and the combination of BRI-Aβ40+42 overexpression resulted in elevated levels of detergent-insoluble Aβ. No significant increase in detergent-insoluble Aβ was seen in the rats expressing APPsw or BRI-Aβ40. No pathological features were noted in any rats, except the AAV-BRI-Aβ42 rats which showed focal, amorphous, Thioflavin-negative Aβ42 deposits.

Conclusion

The results show that AAV-mediated gene transfer is a valuable tool to model aspects of AD pathology in vivo, and demonstrate that whilst expression of Aβ42 alone is sufficient to initiate Aβ deposition, both Aβ40 and Aβ42 may contribute to cognitive deficits.