Genetic evidence for the physiological significance of the D-tagatose 6-phosphate pathway of lactose and D-galactose degradation in staphylococcus aureus

Mutants of Staphylococcus aureus were isolated which were unable to utilize d-galactose or lactose, but which were able to utilize all other carbohydrates tested. Growth of the mutants on a peptone-containing medium was inhibited by d-galactose. Of those mutants selected for further study, one (tagI2) was missing d-galactose 6-phosphate isomerase, one (tagK3) was missing d-tagatose 6-phosphate kinase, and one (tagA4) was missing d-tagatose 1, 6-diphosphate aldolase. Each of these mutants accumulated the substrate of the missing enzyme intracellularly. Spontaneous revertants of each of the mutants simultaneously regained their ability to utilize d-galactose and lactose, lost their sensitivity to d-galactose, regained the missing enzymatic activities, and no longer accumulated intermediates of the d-tagatose 6-phosphate pathway. These data support our previous contention that the physiologically significant route for the metabolism of d-galactose and the d-galactosyl moiety of lactose in S. aureus is the d-tagatose 6-phosphate pathway. Furthermore, a mutant constitutive for all three enzymes of this pathway was isolated, indicating that the products of the tagI, tagK, and tagA genes are under common genetic control. This conclusion was supported by the demonstration that d-galactose 6-phosphate isomerase, d-tagatose 6-phosphate kinase, and d-tagatose 1, 6-diphosphate aldolase are coordinately induced in the parental strain.     

Liberation and Development of Allomyces arbuscula Mitospores Viewed by Scanning Electron Microscopy

Scanning electron microscopy has been employed to examine events in the release and development of mitospores of the aquatic fungus, Allomyces arbuscula. Among the salient features of spore release from the mitosporangium is the digestion of the inner matrix of the exit papillum. Hydrolysis appears to begin at the outer layer of the papillum plug matrix and probably results from activation of localized hydrolytic enzymes. The plug clearly consists of at least two different component layers. Elaboration of mitospores from the mitosporangium is depicted in several micrographs. Motile spores were induced to begin development, and the sequence of surface changes associated with the encystment process was studied. Time course studies show the retraction of the flagellum, the change from elipsoidal to spherical shape, and the deposition of the cell wall. Early in encystment, small vesicles accumulate on the surface of the plasma membrane. These enlarge and fuse to form the mature cyst wall. This surface view of cell wall deposition appears to support the possible role of gamma particles in cell wall synthesis during encystment.     

Potassium Transport and the Relationship Between Intracellular Potassium Concentration and Amino Acid Uptake by Cells of a Marine Pseudomonad

Transport of K(+) by K(+)-depleted cells of marine pseudomonad B-16 (ATCC 19855) exhibited saturation kinetics. Rb(+) inhibited both K(+) transport and the K(+)-dependent transport of alpha-aminoisobutyric acid (AIB) into K(+)-depleted cells of the organism in proportion to the concentration of Rb(+) in the suspending medium. Inhibition of the K(+)-dependent uptake of AIB into K(+)-depleted cells by Rb(+) could be overcome by increasing the concentration of K(+) in the medium. When AIB and K(+) were added simultaneously to a suspension of K(+)-depleted cells, the uptake of K(+) occurred immediately and rapidly, whereas the accumulation of AIB occurred only after a lag. The initial uptake rate of AIB was directly proportional to the intracellular K(+) concentration. The intracellular concentration of K(+) and AIB at their steady-state levels increased to a maximum as the Na(+) concentration in the suspending medium was increased. At Na(+) concentrations between 0.2 and 0.3 M, the molar ratio of K(+) to AIB at their intracellular steady-state concentrations was constant at 1.6. At external Na(+) concentrations less than 0.2 M, the cells maintained a relatively higher K(+) intracellular steady-state level than AIB.     

Regulation of the Pool Size of Valine in Escherichia coli K-12

Three mutations (ilvH611, ilvH612, and ilvH613) are described which make Escherichia coli K-12 resistant to valine inhibition and are located near leu. The expression of the ilv genes appears to be normal in these mutants since the isoleucine-valine biosynthetic enzymes are not derepressed relative to the wild type. The intracellular concentration of valine is, however, higher in the mutants than in the isogenic ilvH(+) strain. These mutants also excrete valine, probably because of the high intracellular concentration of this amino acid. The pool size of valine is regulated independently from that of isoleucine and leucine. The increased intracellular concentration of valine is due to a decreased feedback inhibition that valine exerts on its own biosynthetic pathway. In fact, acetolactate synthase activity assayed in extracts of ilvH612 and ilvH613 mutants is more resistant to valine inhibition than the activity assayed in the ilvH(+) isogenic strain. Two forms of acetolactate synthase activity can be separated from these extracts by adsorption and elution on hydroxylapatite. One of them is as sensitive to valine inhibition as that of the wild type, the other is more resistant to valine inhibition.     

Structural Genes for a Newly Recognized Acetolactate Synthase in Escherichia coli K-12

Evidence is reported that shows the presence in Escherichia coli K-12 of a newly found acetolactate synthase. This enzyme is the product of two genes, ilvH and ilvI, both located very close to leu. Amber mutations have been found in both genes and therefore their products are polypeptides. Mutations in the ilvH gene cause the appearance of an acetolactate synthase activity which is relatively resistant to valine inhibition and can be separated by adsorption on hydroxylapatite from another activity present in the extract and more sensitive to valine inhibition than the former. A mutant altered in the ilvI gene was isolated among the revertants sensitive to valine inhibition of an ilvH mutant. Such a mutant lacks the resistant acetolactate synthase. A temperature-sensitive revertant of the ilvI mutant contained a temperature-sensitive acetolactate synthase. Thus ilvI is the structural gene for a specific acetolactate synthase. The activity of the ilvH gene product has been measured by adding an extract containing it to a purified ilvI acetolactate synthase, which, upon incubation, became more sensitive to valine inhibition. Conversely, a valine-sensitive acetolactate synthase (the product of the ilvH and the ilvI genes) became more resistant to valine inhibition upon incubation with an extract of a strain containing a missense ilvH gene product.     

Mutation in Saccharomyces cerevisiae Conferring Streptomycin and Cold Sensitivity by Affecting Ribosome Formation and Function

A cold-sensitive, streptomycin-sensitive mutant of Saccharomyces cerevisiae accumulates a 28S ribonucleoprotein particle when grown at low temperature. This particle contains 17S ribosomal ribonculeic acid which is degraded when exposed to ribonuclease. The particle does not serve as a precursor to 60 and 40S ribosomal subunits nor is it turned over when growth is allowed to resume at the permissive temperature; rather it is only diluted by growth. That streptomycin sensitivity (allelic with cold sensitivity) is ribosomal is evidenced by the inhibition of protein synthesis in vitro by streptomycin and the binding of labeled streptomycin to the mutant but not the parental 40S ribosomal subunit.     

Phase transformation and chiasma frequency variation in locusts

Locusts exhibit two basic forms or phases, one characteristic of swarming populations, termed phase gregaria, and the other characteristic of low density populations, termed phase solitaria. It has been claimed by Nolte that locusts living at low density, both in the field and in the laboratory, have a reduced chiasma frequency compared with animals living at high density. A postulated gregarisation pheromone is held to be responsible for the stimulation of melanin biosynthesis in the swarming animals and an unknown metabolite in this pathway causes the increase in chiasma frequency, as well as other phenotypic changes associated with phase transformation. According to Nolte this represents a means of releasing stored genetic variation necessary for adaptation in the areas invaded by swarms. — This claim has been re-examined in laboratory stocks of Schistocerca gregaria using a methodology comparable to that of Nolte. No reduction in the chiasma frequency of isolated animals was observed in any of the experiments. The isolated animals did, however, develop a phenotype characteristic of phase solitaria in terms of their pigmentation and morphometrics.     

B-chromosome behaviour in Phaulacridium vittatum

Nine individuals of Phaulacridium vittatum in a single population sample of 1250 males collected at Crookwell, N. S.W. contained a single supernumerary chromosome. One further individual had two B-chromosomes. The supernumerary in question was larger than any of the standard set and was distinguishable from them at all stages of mitosis and meiosis. Like the X-univalent the B-chromosome was heteropycnotic at the onset of meiosis but differed from it in size, structure and behaviour. During first prophase single supernumeraries were frequently associated with the X in a non-homologous fashion as a consequence of their precocity. All such associations lapsed before first metaphase and the X and the B moved at random with respect to one another at first anaphase. In the one individual with two supernumeraries the two B-chromosomes showed regular pairing and segregated in a conventional manner. In all these respects the Crookwell supernumerary differed markedly from a morphologically identical B-chromosome present in a population of the same species from Hobart, Tasmania studied by Jackson and Cheung in 1967. Whether these differences in the behaviour of the B-chromosome in the two populations determines the higher frequency of the supernumerary in Hobart (11.3%) as compared with Crookwell (0.8%) remains to be resolved.