Purification, Ultrastructure, and Composition of Axial Filaments from Leptospira

The ultrastructure of three strains of water Leptospira was studied by negative staining, thin sectioning, and freeze-etching. The cells possessed a triple-layered sheath which covered two independent axial filaments, one inserted subterminally in each end of the cell. The protoplasmic cylinder was surrounded by a triple-layered cell wall and possessed ribosomes, lamellar structures, and a typical procaryotic nuclear region. The axial filament was comprised of several component structures. An axial fibril, with a diameter of 20 to 25 nm, consisted of a solid inner core (13 to 16 nm in diameter) surrounded by a coat. A terminal knob (40 to 70 nm in length) was connected to a series of disc insertion structures at the terminal end of the axial fibril. The axial fibril was surrounded by a helical outer coat (35 to 60 nm in diameter) which was composed of a continuously coiled fiber, 3 to 4 nm in diameter, embedded in an electron-dense material. A procedure for the purification of the axial fibrils was presented and their ultrastructural, physical, and chemical properties were determined. Similarities in ultrastructural, physical, and chemical properties were noted between the axial fibrils and bacterial flagella. A schematic model of the leptospiral axial filament is presented, and a mechanism is proposed for its function as a locomotor organelle.     

Penicillin production and its mode of inheritance inAspergillus nidulans

Previous workers have shown that some strains ofAspergillus nidulans produce penicillin-like substances. In the present studies, shake-flask cultures of 101 wild-type strains ofA. nidulans, representatives of 18 different heterokaryon-compatible groups, were examined and filtrates of most found to inhibit the growth of a strain ofBacillus subtilis sensitive to penicillin, although members of two of these groups had no detectable antibiotic activity. Five strains with antibacterial properties were chosen for detailed investigation as well as two genetically labelled derivatives obtained from one of these after ultraviolet light treatments; one derivative had a similar antibiotic yield to its original wild-type parent but the other was selected as having increased antibiotic yield. The antibiotic produced by these seven strains was by all tested criteria, including chromatographic and electrophoretic behaviour, indistinguishable from penicillin. A heterokaryon test between the two mutants indicated that antibiotic productivity was under nuclear control.     

Expression of the trpC gene from Penicillium chrysogenum in Aspergillus nidulans

The heterologous expression in Aspergillus nidulans of a gene involved in tryptophan biosynthesis from Penicillium chrysogenum is described. With the chimeric plasmid pPC-31, which carries the cloned trpC gene, approximately 10-40 "stable" transformants per microgram of DNA were obtained, with selection for complementation of the mutant allele. This frequency was increased 10-fold by the insertion of the ans1 fragment into the transformation vector. Southern hybridization analysis revealed that transformation occurred as a consequence of the integration of vector sequences into the host chromosome at a variety of sites within the genome.     

Molecular cloning and characterization of the spaB gene of Streptococcus sobrinus

A gene of Streptococcus sobrinus 6715 (serotype g) designated spaB and encoding a surface protein antigen was isolated from a cosmid gene bank. A 5.4 kb HindIII/AvaI DNA fragment containing the gene was inserted into plasmid pBR322 to yield plasmid pXI404. Analysis of plasmid-encoded gene products showed that the 5.4 kb fragment of pXI404 encoded a 195 kDa protein. Southern blot experiments revealed that the 5.4 kb chromosomal insert DNA had sequence similarity with genomic DNA of S. sobrinus 6715, S. sobrinus B13 (serotype d) and Streptococcus cricetus HS6 (serotype a). The recombinant SpaB protein (rSpaB) was purified and monospecific antiserum was prepared. With immunological techniques and the anti-rSpaB serum, we have shown: (1) that the rSpaB protein has physico-chemical and antigenic identity with the S. sobrinus SpaB protein, (2) the presence of cross-reactive proteins in the extracellular protein of serotypes a and d of the mutans group of streptococci and (3) that the SpaB protein is expressed on the surface of mutans streptococcal serotypes a, d and g.     

The dentinoenamel junction and the hypocone in primates

Enamel has been stripped from primate teeth (especially humans and ceboids) with special reference to the comparative form of the hypocone. Dentally reduced species show variable developments not always expected of a hypothetical ontogenetically prior stage.     

Triazine Resistance in Senecio vulgaris Parental and Nearly Isonuclear Backcrossed Biotypes Is Correlated with Reduced Productivity

Isonuclear triazine-susceptible and triazine-resistant Senecio vulgaris L. biotypes were developed by making reciprocal crosses between susceptible and resistant biotypes to obtain F₁ hybrids and backcrossing the hybrids to the appropriate pollen parent. The electrophoretic isozyme patterns of the enzyme aconitase obtained from leaf extracts of triazine-susceptible parental (S) and backcrossed (S×R_BC6) biotypes, and triazine-resistant parental (R) and backcrossed (R×S_BC6) biotypes verified that the biotypes had the expected nuclear genomes. Atrazine inhibition of chloroplast whole chain electron transport from water to methyl viologen was measured to verify susceptibility or resistance to triazine herbicides. The photosynthetic rate and biomass accumulation of greenhouse grown susceptible and resistant S. vulgaris biotypes were measured 28, 35, 42, 50, 57, and 64 days after planting to determine the effect of altered chloroplast function. S and S×R_BC6 biotypes had CO₂ assimilation rates of 16.2 and 16.6 micromoles CO₂ per square meter per second, respectively, and I₅₀ values (herbicide concentration producing 50% inhibition) of about 0.49 micromolar atrazine. The corresponding values for the R and R×S_BC6 biotypes were 14.7 and 14.6 micromoles CO₂ per square meter per second with I₅₀ values of 65.0 micromolar atrazine. The S biotype was larger and more productive than the R biotype at all harvests. At the harvest 57 days after planting, mean shoot dry weight was 33.2 and 8.7 grams for the S and R biotypes, respectively. The growth effect associated with chloroplast differences was shown in comparisons of the S biotype with the R×S_BC6 biotype and of the S×R_BC6 biotype with the R biotype. The R×S_BC6 biotype had 72% of the shoot dry weight of the S biotype while the R biotype had 55% of the shoot dry weight of the S×R_BC6 biotype. The R×S_BC6 and R biotypes produced about 73 and 62% of the leaf area of the S and S×R_BC6 biotypes, respectively. Relative growth rate was similar in biotypes with the same nuclear genome; however, instantaneous unit leaf rate was higher in the S compared to the R×S_BC6 biotype and in the S×R_BC6 compared to the R biotype. At 57 days after planting, the cumulative leaf area duration (i.e. photosynthetic opportunity) of the R×S_BC6 and R biotypes was 86 and 66% of that of the S and S×R_BC6 biotypes, respectively. Our data indicate that impaired chloroplast function in triazine resistant S. vulgaris biotypes limits growth and productivity at the whole plant level.