The effects of growth in human serum on an acapsular group B Streptococcus mutant.

A Group B Streptococcus Type III (GBS) mutant which, when grown in Todd Hewitt broth (THB), does not produce any detectable capsule, produced a clearly visible polysaccharide capsule when grown in human serum. We isolated cytoplasmic membranes from GBS and separated the component membrane proteins by polyacrylamide gel electrophoresis. A significant change in membrane composition was found during growth in human serum. Several unique proteins were produced on serum growth and there was both up- and down-regulation of other proteins. We measured the intracellular levels of sialic acid for a variety of GBS serotype III isolates. Interestingly, while there was little difference between the intracellular sialic levels of most isolates, the sialic acid level of COH31-15 grown in THB was over 100% higher than that of any other isolate. When grown in serum this pool was reduced to a level similar to that in other strains. The concentration of bacterial cell sialic acid was directly correlated with the sialic acid content of the serum. Exogenous sialic acid content, in concert with other serum factors, plays a role in determining the capsular size in GBS.

Localization and characterization of hemoglobin-degrading aspartic proteinases from the malarial parasite Plasmodium falciparum.

Three hemoglobin-degrading proteinases were partially purified from food vacuoles isolated from trophozoite-stage forms of the malarial parasite Plasmodium falciparum. Two of the proteinases (M1 and M2) were solubilized by repeated sonication. The remaining proteinase (M3) was solubilized by treatment of the particulate fraction with taurocholic acid, suggesting that proteinase M3 is a membrane-bound proteinase whereas proteinases M1 and M2 are weakly associated with parasite membrane. The location of these proteinases suggests that they may participate in the digestion of host cytosolic protein. After partial purification, but not before, proteinases M1, M2 and M3 are highly sensitive to pepstatin, supporting their designation as aspartic proteinases. These aspartic proteinases show broad specificity for protein substrates. Native hemoglobin, acid denatured hemoglobin and oxidatively damaged hemoglobin are comparable substrates. Hemoglobin within the food vacuole was shown to be primarily native hemoglobin. Chemical modification studies indicate that these three aspartic proteinases have similar properties. The peptide maps from degradation of hemoglobin, however, suggest that aspartic proteinases M1, M2 and M3 are distinct proteinases.

Water and urea transport in human erythrocytes infected with the malaria parasite Plasmodium falciparum.

The permeability properties of the human red cell membrane to various solutes are altered by malarial infection. In the present work we show that the permeability of the red cell membrane to water is also affected by the intraerythrocytic growth of the malaria parasite Plasmodium falciparum, whereas urea permeability appears unchanged. The data from infected cells show decreases in membrane surface area, cell volume, the osmotically active water fraction (Weff), and osmotic water permeability (Pf) as measured by stopped-flow spectroscopy. On the other hand, the data suggest an increase in diffusive water permeability (Pd) in infected cells with no change in urea permeability when measured by the continuous flow method. The decreased Pf/Pd ratio of infected cell membranes and its implications in the geometry of the red cell membrane water channel or pore are discussed.

DNA base composition, nature of intracellular DNA, morphology, and classification of bacteriophages infecting Micrococcus luteus.

Ten bacteriophages infecting Micrococcus luteus have been characterized. All phages contain double-stranded DNA, of 64.3--73.5 mol% guanine plus cytosine (GC). The DNA of phage N7 has the highest GC content reported for any bacterial virus. No unusual bases have been found. The intracellular replicating DNAs of six phages are covalently closed circular molecules. All 10 phages have isometric, probably icosahedral, heads and long, flexible, noncontractile tails and can be sorted into two morphological groups based on size and presence or absence of a collar. Host-range studies indicate six host-range groups.

Topologic forms of mitochondrial DNA in AKR mice.

Circular dimer forms of mitochondrial DNA were found in leukemic and preleukemic AKR mice but not in nonleukemic animals. There was a positive correlation between the presence of circular dimers and progression of the disease, the leukemic mice having the greatest evidence of circular dimers. This finding suggested that the occurrence of early subcellular changes is an important cellular modification in the leukemogenic process.

Preservation of myelin lamellar structure in the absence of lipid. A correlated chemical and morphological study.

The fine structure of myelin was studied in glutaraldehyde-fixed rat sciatic nerves depleted of lipid by acetone, chloroform:methanol (2:1 v/v), and chloroform:methanol:concentrated HCl (200:100:1, v/v/v). One portion of each of these nerves, plus the extracts, was saponified and analyzed by gas-liquid chromatography for fatty acids. The remainder of each nerve was stained in osmium tetroxide in CCl(4) (5g/100cc) and was embedded in Epon 812. Thin sections, examined in the electron microscope, revealed the preservation of myelin lamellar structure with a 170 A periodicity in nerves depleted of 98% of their lipids. Preservation of myelin lamellar structure depended on glutaraldehyde fixation and the introduction of osmium tetroxide in a nonpolar vehicle (CCl(4)) after the lipids had been extracted. It is concluded that the periodic lamellar structure in electron micrographs of myelin depleted of lipid results from the complexing of osmium tetroxide, plus uranyl and lead stains, with protein.