THE DIFFERENTIAL SENSITIVITY OF CULTURED CHICK MESODERMAL CELLS TO ACTINOMYCIN D

Cells were isolated from the somite mesoderm and from the unsegmented (presomite) mesoderm of early chick embryos and exposed to actinomycin D in single cell culture. Actinomycin D inhibited proliferation in cell cultures derived from the unsegmented mesoderm, although the same concentrations of this antibiotic did not inhibit cultures derived from the somite mesoderm. This differential sensitivity parallels the regionally specific necrosis and degeneration observed in the unsegmented mesoderm of intact chick embryos exposed to actinomycin D. In culture, both cell types exhibited approximately the same permeability to labeled actinomycin D and showed comparable inhibition of RNA, DNA, and protein syntheses in the presence of the antibiotic. However, freshly isolated mesodermal cells from the somite region had a higher content of RNA than did cells from the unsegmented region, and the somite cells maintained a higher rate of macromolecular synthesis in untreated cultures.     

Evaluation of Factors Related to Growth of Rift Valley Fever Virus in Suspended Cell Cultures

The effect of several controlled variables on the peak titer and fold increase of Rift Valley fever virus grown in suspension culture on two variants of Earle's L cell, L-DR and L-MA clone 1-1, was studied. No significant amount of cell-associated virus was found at 24 hr, indicating a release of virus soon after its formation. Mild sonic treatment of the virus produced in serum-free medium increased the infective titer about 10x. This difference was not observed with virus produced in medium supplemented with serum. Peak titer was not affected by medium used during the infection period, by multiplicity of inoculum (MOI), or by initial cell concentration within the test range of 10(4) to 2 x 10(6) cell/ml. Cell strain employed influenced titer, because the L-DR cell did not produce virus efficiently at low MOI and low initial cell concentration. The time of peak titer and fold replication was dependent on MOI and initial cell concentration. Differences in virus propagation in monolayer and suspension systems are discussed.     

Oxidation ofn-alkanes to ketones by anArthrobacter species

AnArthrobacter strain isolated from soil and selected for poor ability to utilize hexadecane as sole C-source was grown in a hexadecane (or pentadecane) — salts medium supplemented with yeast extract or corn steep liquor as the source of carbon for growth. It accumulated mono-hexadecanones (or pentadecanones). The percentages to which the individual ketones were accumulated depended on the distance of the carbonyl group from the terminal end of the substrate hydrocarbon; the greater the distance, the lower the percentage. The percentages did not depend on the composition of the medium. No other hydrocarbon oxidation products were observed.These results are discussed in relation to other reports of microbial conversions of alkanes to ketones.This research was authorized for publication as paper no. 3331 in the journal series of the Pennsylvania Agricultural Experiment Station, on December 7, 1967.     

Membranes of Saccharomyces cerevisiae

A crude small particle pellet, obtained from postmitochondrial supernatant fractions of Saccharomyces cerevisiae, contains about half the ergosterol and phospholipid of crude cell homogenates. Most of the phospholipid of this pellet is in a “heavy” fraction which, with the aid of electron microscopy, shows membranous elements in addition to discrete particles. The “heavy” fraction, upon treatment with deoxycholate, can be freed of membranes, or, with ribonuclease treatment, ribosomes can be removed, leaving relatively clean membranes. The “heavy” fraction resembles the microsomes of animal cells, but contains considerably less lipids, including phospholipids, thus suggesting a less well-developed intracellular membrane system.