Arginine utilization by Mycoplasma fermentans is not regulated by glucose metabolism: A 13C-NMR study

Abstract Electrofusion of protoplasts of two mutant strains of Hansenula polymorpha resulted in high fusion and hybrid yields when the calcium ions present in the conventional fusion medium replaced by zinc ions. The optimal fusion conditions were an alignment field of 0.4 kV cm⁻¹ strength and 2 MHz frequency for 30 s, followed by two consecutive pulses of 12 kV cm⁻¹ strength and 15 μs duration. With 0.05–0.1 mM zinc ions in the fusion medium an average clone number of 10⁴–10⁵ clones per 10⁸ input cells was reached. The presence of about 0.6 mM magnesium ions in the zinc fusion medium was essential.     

Solid-Supported Oligonucleotide Systems for Special Biomedical Applications

Abstract

The use of composite beads consisting of a 6 μm polystyrene core with 30 nm surface-bound silica particles to routine automatic oligodeoxynucleotide (ODN) synthesis is described.     

Lipopolysaccharide size and distribution determine serum resistance in Salmonella montevideo.

The survival of Salmonella montevideo during serum treatment depends on the presence of an O antigen (O-Ag) associated with the lipopolysaccharide molecule. In this organism, the O antigen is a polysaccharide composed of 0 to more than 55 subunits, each containing 4 mannose residues together with glucose and n-acetylglucosamine. We used a mutant strain of S. montevideo that requires exogenous mannose for the synthesis of O-Ag. Lipopolysaccharide (LPS) was prepared from these cells grown under three different conditions where the availability of exogenous mannose was regulated such that the average number of O-Ag units per LPS molecule, the percentage of LPS molecules bearing long O-Ag side chains, and the percentage of lipid A cores bearing O-Ag were all varied. These changes in LPS profiles were monitored on sodium dodecyl sulfate-polyacrylamide gels, and cells with different LPS profiles were tested for their ability to survive treatment with pooled normal human serum. Survival in serum was associated with LPS that contained an average of 4 to 5 O-Ag units per LPS molecule, and 20 to 23% of the LPS molecules had more than 14 O-Ag units per LPS molecule. Serum survival was less clearly associated with the percentage of lipid A cores covered with O-Ag. We propose, based on these data and on previous work, that the O-Ag polysaccharide provides the cell protection from serum killing by sterically hindering access of the C5b-9 complex to the outer membrane and that a critical density of long O-Ag polysaccharide is necessary to provide protection.