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The pink yeast Rhodotorula rubra of marine origin was found to be capable of extended growth at very low phosphate concentrations ( K 0.5 = 10.8 n m ). Average intracellular phosphate concentrations, based on isotope exchange techniques, were 15 to 200 n m , giving concentration gradients across the cell envelope of about 10 6 . Sensitivity to metabolic inhibitors occurred at micromolar concentrations. Inability of the phosphate transport system, K s = 0.5 to 2.8 μ m , V max = 55 μmoles per g of cells per min, to discriminate against arsenate transport led to arsenate toxicity at 1 to 10 n m , whereas environmental arsenate levels are reportedly much higher. Phosphate competitively prevented arsenate toxicity. The K i for phosphate inhibition of arsenate uptake was 0.7 to 1.2 μ m . Phosphate uptake experiments showed that maximal growth rates could be achieved with approximately 4% of the total phosphate-arsenate transport system. Organisms adapted to a range both of concentration of NaCl and of p H. Maximal affinity for phosphate occurred at p H 4 and at low concentrations of NaCl; however, V max for phosphate transport was little affected. Maximal specific growth rates on minimal medium were consistent in batch culture but gradually increased to the much higher rates found with yeast extract media when the population was subjected to long-term continuous culture with gradually increasing dilution rates. Phosphate initial uptake rates that were in agreement with the steady-state flux in continuous culture were obtained by using organisms and medium directly from continuous culture. This procedure resulted in rates about 500 times greater than one in which harvested batch-grown cells were used. Discrepancies between values found and those reported in the literature for other organisms were even larger. Growth could not be sustained below a threshold phosphate concentration of 3.4 n m . Such thresholds are explained in terms of a system where growth rate is set by intracellular nutrient concentrations. Threshold concentrations occur in response to nutrient sinks not related to growth, such as efflux and endogenous metabolism. Equations are presented for evaluation of growth rate-limiting substrate concentrations in the presence of background substrate and for evaluating low inhibitor concentration inhibition mechanisms by substrate prevention of inhibitor flux.

The pleiotropic ctr mutation has been shown to affect tryptophan uptake and tryptophanase formation. Genetic reversions are of two types: (i) complete, restoring to wild type, located at 46 to 47 min; (ii) partial, restoring only tryptophanase synthesis, located at 73 min. In some strains the effect of ctr mutations could be reversed by cyclic adenosine 3′,5′-monophosphate (cAMP) plus tryptophan. A mutant producing tryptophanase constitutively was suppressed by a ctr mutation. Production of tryptophanase in this suppressed strain was not restored by the addition of cAMP, but required cAMP plus tryptophan.

The metabolism of lactose was found to be controlled by three genes: a gene for the synthesis of a β-galactosidase attacking only phosphorylated galactosides; a gene for a protein permitting concentration of phosphorylated galactosides which probably acts by transferring phosphates to them; and a gene regulating the first two structural genes. The three genes are closely linked and may have the same order as in Escherichia coli . Galactose-6-phosphate was found to be a better inducer of lactose utilization than is galactose or any other inducer. The inhibition of induction by isopropylthiogalactoside was found to occur at the level of the protein permitting the concentration of galactoside phosphates.

A test procedure based on complementation in mixed extracts is described for the assay of heat-stable protein and enzyme I of the phosphoenolpyruvate-dependent phosphotransferase system. The test was used to assay a collection of pleiotropic carbohydrate mutants of Escherichia coli ( ctr mutants) and revertants of these mutants. All mutants were found to lack enzyme I of the phosphoenolpyruvate-dependent transferase system. Revertants of these mutants to complete wild phenotype regained enzyme I-forming ability. Reversion to partial wild type was not accompanied by restoration of enzyme I-forming ability.

Morse , M. L. (University of Colorado Medical Center, Denver) and J. W. LaBelle . Characteristics of a staphylococcal phage capable of transduction. J. Bacteriol. 83: 775–780. 1962—The growth of staphylococcal phage 53, a temperate phage, has been studied. The latent periods in nutrient broth are: infected sensitive cells, 45 min; ultraviolet-induced lysogenic cells, 83 min. The burst size, as indicated by one-step growth studies and single-burst experiments, is 25 to 30 particles per lysing cell. Phage particles transducing streptomycin resistance and novobiocin resistance are produced at the same time as nontransducing particles. Some observations have been made on the host, Staphylococcus aureus NCTC 8511.

The gal-3 mutation, which had been shown previously to produce unstable revertants, was combined in three instances with recA , a mutation which suppresses recombination. Unstable revertants were produced in the gal-3 recA recombinants qualitatively as frequently as in the absence of the recA gene, and it is concluded that a recombination mechanism is not the basis of the instability observed.

The reversion behavior of pleiotropic carbohydrate mutants, previously designated as ctr , was studied. The mutants revert to complete restoration of the wild-type phenotype, as well as to a spectrum of partial wild-type phenotypes. Lac + reversions were found in the lac region (11 min) and some Mal + reversions occurred at malB (79 min), at a distance from the site of the ctr mutations (46 to 47 min). About one-third of Lac + and Mal + revertants were constitutive for uptake of their respective substrates, and one-third modified for inducibility. The remaining third were not distinguishable from wild type. Induction of a ctr mutation in a lac constitutive strain, either operator or repressor mutant, did not affect lactose metabolism. A polar-like ctr mutant, deficient in both enzyme I and heat-stable protein of the phosphoenolpyruvate-dependent phosphotransferase strain was also described. Partial revertants of ctr were still found to lack enzyme I.