Electron microscopic and biophysical studies of liposome membrane structures to characterize similar features of the membranes of Streptomyces hygroscopicus

To characterize the novel non-planar plasma membrane structure of bacteria (wafer structure), liposome membranes from the bacterial lipid mixture and individual lipid fractions were prepared and investigated by freeze-fracture electron microscopy, microcalorimetry and 31P-NMR spectroscopy. The phospholipid content of the membranes is essential for the formation of the non-planar membrane structure and there is no indication that the formation of the structure is connected with temperature-induced lipid phase transition processes. An exaggerated form of the wafer structure (raspberry structure) is also visible and additionally, in both cases, many small spherical vesicles are observed. We suggest that both membrane features of the liposomal and bacterial membranes are induced by these vesicles, forming a hexagonal or cubic organization of vesicles on the cytoplasmic surface of the biological membrane, and in between the multilamellae in the artificial membranes.     

Phosotynthesis in hemiepiphytic species of Clusia and Ficus

Summary Hemiepiphytic species in the genera Clusia and Ficus were investigated to study their mode of photosynthetic metabolism when growing under natural conditions. Despite growing sympatrically in many areas and having the same growth habit, some Clusia species show Crassulacean acid metabolism (CAM) whereas all species of Ficus investigated are C₃. This conclusion is based on diurnal CO₂ fixation patterns, diurnal stomatal conductances, diurnal titratable acidity fluctuations, and ¹³C isotope ratios. Clusia minor, growing in the savannas adjacent to Barinas, Venezuela, shows all aspects of Crassulacean acid metabolism (CAM) on the basis of nocturnal gas exchange, stomatal conductance, total titratable acidity, and carbon isotope composition when measured during the dry season (February 1986). During the wet season (June 1986), the plants shifted to C₃-type gas exchange with all CO₂ uptake occurring during the daylight hours. The carbon isotope composition of new growth was-28 to-29 typical of C₃ plants.     

Effect of serotonin (5-HT) and other monoamines on murine macrophages: modulation of interferon-gamma induced phagocytosis

We have previously shown that serotonin (5-HT) suppresses interferon-gamma (IFN-gamma)-induced Ia expression. In the present report, we show that 5-HT as well as other monoamines, histamine and dopamine, modulate IFN-gamma-induced phagocytosis in murine bone marrow macrophages. The effect of 5-HT on IFN-gamma-induced phagocytosis varied according to the concentration of IFN-gamma to which the macrophages were exposed. At low concentrations of IFN-gamma, 5-HT augmented phagocytosis, whereas at high concentrations of IFN-gamma, 5-HT suppressed phagocytosis. At both low and high IFN-gamma concentrations the response to 5-HT was dose-related and occurred at physiologic concentrations; the half-maximal effect was 6 X 10(-7) M and 3 X 10(-7) M for low and high IFN-gamma concentrations, respectively. Both histamine and dopamine also augmented IFN-gamma (1 U/ml) induced phagocytosis, at half-maximal augmenting concentrations of 7 X 10(-8) M and 4 X 10(-7) M, respectively. The 5-HT effects were blocked by the 5-HT antagonists spiperone, ketanserin, LY53857, mCPP, and PAPP, but not by the histamine antagonists pyrilamine, chlorpheniramine, or cimetidine. Histamine augmentation of IFN-gamma-induced phagocytosis was blocked by the H1 antagonists pyrilamine and chlorpheniramine, but not by the H2 antagonist cimetidine. The dopamine effect was blocked by spiperone and pyrilamine, both of which have been shown to block dopaminergic effects in other systems. This data provides functional evidence that at least part of the modulation of IFN-gamma-induced phagocytosis by 5-HT occurs through a 5-HT receptor-mediated mechanism, and 5-HT, dopamine, and histamine modulate IFN-gamma-induced phagocytosis independently through their respective receptors.     

Recognition and cleavage of the bacteriophage P1 packaging site (pac). I. Differential processing of the cleaved ends in vivo

The packaging of bacteriophage P1 DNA into viral capsids is initiated at a specific DNA site called pac. During packaging, that site is cleaved and at least one of the resulting ends is encapsidated into a P1 virion. We show here that pac is located on a 620 base-pair fragment of P1 DNA (EcoRI-20). When that fragment is inserted into the chromosome of cells that are then infected with P1, packaging of host DNA into phage particles is initiated at pac and proceeds down the chromosome, unidirectionally, for about five to ten P1 "headfuls" (about 5 X 10(5) to 10 X 10(5) bases of DNA). Using an assay for pac cleavage that does not depend on DNA packaging, we have identified a set of five amber mutations that are mapped adjacent to pac, and that define a gene (gene 9) essential for pac cleavage. Amber mutations that are located in genes necessary for viral capsid formation (genes 4, 8 and 23), or in a gene necessary for "late" protein synthesis (gene 10), do not affect pac cleavage. The latter result suggests that the synthesis of the pac cleavage protein is not regulated co-ordinately with other phage morphogenesis proteins. The products of pac cleavage were analyzed using two different DNA substrates. In one case, a single copy of pac was placed in the chromosome of P1-sensitive cells. When those cells were infected with P1, we could detect the cleavage of as much as 70% of the pac-containing DNA. The pac end destined to be packaged in the virion was detected five to 20 times more efficiently than was the other end. Since this result is obtained whether or not the infecting P1 phage can encapsidate the cut pac site, the differential detection of pac ends is not simply a consequence of one end being packaged and the other not. In a second case, pac was located in cells on a small (5 X 10(3) bases) multicopy plasmid. When those cells were infected with P1, neither pac end was detected efficiently after P1 infection, unless the cells carried a recBCD- mutation. In recBCD- cells, the results with plasmid-pac substrates were similar to those obtained with chromosomally integrated pac substrates. We interpret these results to mean that, following pac cleavage, the end destined to be packaged is protected from cellular nucleases while the other end is degraded by the action of at least two nucleases, one of which is the product of the host recBCD gene.(ABSTRACT TRUNCATED AT 400 WORDS)     

Predictions of linear T-cell and B-cell epitopes in proteins encoded by HIV-1, HIV-2 and SIVMAC and the conservation of these sites between strains

An important consideration in the design of vaccines to prevent HIV-1 infection effective against different strains is the amino acid sequence conservation of antigenic determinants. Even one amino acid change can destroy the antigenicity of a site for the antibody or T-cell receptor. The comparisons of predicted T- and B-cell epitopes between human HIV-1, HIV-2 and monkey SIVMAC AIDS viruses are presented. The three major gene products (env, gag and pol) were examined. A number of epitopes were identical between strains of HIV-1. Our analysis highlights the problem of designing an effective HIV-1 and HIV-2 vaccine and also the problem of testing human vaccines in monkey models.     

Stable carbon isotope ratio of tree leaves, boles and fine litter in a tropical forest in Rondônia, Brazil

Leaves of 208 trees were collected for isotopic analysis together with wood from 36 tree boles and 18 samples of fine litter from a terra-firme forest located at Samuel Ecological Reserve, Rondônia State, in the southwestern Amazon region. The range of δ¹³C values in leaves was from ?28 to ?36‰, with an average (±1 SD) of ?32.1?±?1.5‰, which was more negative than the δ¹³C values of bole samples (?28.4?±?2.0‰) and fine litter (?28.7?±?2.0‰). These values are within the range found for tropical and subtropical forests. Pooling the δ¹³C values for leaf samples from trees of the same height gave averages which were positively correlated with plant height at a highly significant level, with a slope of 0.06 and an intercept of ?33.3‰ and a correlation coefficient r ²=0.70 (P<0.001).     

Establishment of New Genetic Traits in a Microbial Biofilm Community

Conjugational transfer of the TOL plasmid (pWWO) was analyzed in a flow chamber biofilm community engaged in benzyl alcohol degradation. The community consisted of three species, Pseudomonas putida RI, Acinetobacter sp. strain C6, and an unidentified isolate, D8. Only P. putida RI could act as a recipient for the TOL plasmid. Cells carrying a chromosomally integrated lacI^q gene and a lacp-gfp-tagged version of the TOL plasmid were introduced as donor strains in the biofilm community after its formation. The occurrence of plasmid-carrying cells was analyzed by viable-count-based enumeration of donors and transconjugants. Upon transfer of the plasmids to the recipient cells, expression of green fluorescence was activated as a result of zygotic induction of the gfp gene. This allowed a direct in situ identification of cells receiving the gfp-tagged version of the TOL plasmid. Our data suggest that the frequency of horizontal plasmid transfer was low, and growth (vertical transfer) of the recipient strain was the major cause of plasmid establishment in the biofilm community. Employment of scanning confocal laser microscopy on fixed biofilms, combined with simultaneous identification of P. putida cells and transconjugants by 16S rRNA hybridization and expression of green fluorescence, showed that transconjugants were always associated with noninfected P. putida RI recipient microcolonies. Pure colonies of transconjugants were never observed, indicating that proliferation of transconjugant cells preferentially took place on preexisting P. putida RI microcolonies in the biofilm.