- Volume 82, Issue 1, 1974

SUMMARY A membrane-bound sulphite oxidase from Thiobacillus denitrificans uses nitrate, oxygen or ferricyanide as an electron acceptor and is not stimulated by AMP. Studies with inhibitors of oxygen uptake indicated that an electron-transport chain is involved during sulphite oxidation. The inhibition of oxygen uptake by nitrate was found to be of the non-competitive type. The enzyme, which was purified about 50-fold, used ferricyanide as an electron acceptor, but neither nitrate nor oxygen was utilized. Thiol-binding reagents strongly inhibited the enzyme and this was completely reversed by dithiothreitol. The optimum pH was 8·3 with a Km of 0·5 mm for sulphite.

SUMMARY Cytochromes of the c, a and d types have been detected in crude extracts of Thiobacillus denitriflcans. In the membrane fraction (P 144), cytochromes of the c and d types reduced by sulphide under anaerobic conditions were reoxidized by either oxygen or nitrite. Sulphite, however, reduced only cytochrome c, which was reoxidized by nitrate and oxygen but not by nitrite. In the S 144 fraction, cytochromes of the c and a types reduced by sulphite were reoxidized by oxygen but nitrate and nitrite were ineffective. Cytochromes of the a and d types combined with CO and these effects were reversed by light. Inhibitor studies on sulphide oxidation linked to either oxygen uptake or nitrite reduction indicated that flavin, a terminal oxidase and copper may be involved. A scheme of electron transport during sulphide and sulphite oxidation is proposed.

SUMMARY Enniatins were determined in the mycelium of Fusarium sambucinum grown in liquid surface culture on semidefined or undefined media. Light was required for significant enniatin production, which was also favoured by moderate growth temperature. Production was supported by various carbon and nitrogen sources. Growth on a medium containing (w/v) 5 % lactose and 0·8 % tryptone, at 20 °C, with daily 12 h photoperiods, yielded 1·7 g enniatins/1 (10 % of mycelial dry wt). Glucose inhibited sporulation of F. sambucinum.

SUMMARY Isolation of α mating-type yeasts from a conjugation mixture permitted the direct demonstration of inhibition of DNA synthesis in these cells as a necessary prelude for zygote formation in yeast.

SUMMARY A mutant induced by nitrosoguanidine in the Challis (group H) strain of Streptococcus contains a number of separable mutations linked to each other and to the locus governing sensitivity to streptomycin. One suppresses the level of resistance conferred by mutations in the streptomycin-sensitivity locus, two confer sensitivity to mitomycin and one confers sensitivity to ultraviolet radiation. None of these mutations affects transformability with either homologous or heterologous DNA. However, with the suppressor in the recipient strain there is a loss of streptomycin-resistant transformants, dependent upon the level of resistance conferred by the donor streptomycin-resistance marker and the degree of linkage between the suppressor and that marker.

Summary: The morphological effect of potassium cyanide on the aerobic germination of spores of Mucor rouxii (nrrli1894) in the presence of glucose was investigated. At concentrations of up to 2 mm-KCN, normal filaments were formed; at concentrations of 3 to 6 mm intermediate forms were observed ranging from enlarged and septated hyphae to rounded multipolar cells; at 8 mm spores produced only budding spherical cells. The effect of glucose on the anaerobic germination of spores was also studied. At 0·01 % glucose hyphal development occurred, whereas at increasing concentrations dimorphic colonies were formed. At 2 % glucose purely yeast colonies appeared of the type described by Bartnicki-García (1968) for Mucor rouxii ym8o. In the absence of glucose, or when glucose was replaced by xylose, maltose or succinate, spores did not germinate.

Anaerobiosis did not prevent the elongation of preformed hyphae obtained under aerobic conditions, provided that the cellular integrity was maintained. The anaerobic mycelia had a fermentative metabolism, as indicated by the low level of cytochrome oxidase, the amount and the type of pyruvate kinase, and the production of ethyl alcohol. Conversion of hyphal to yeast-like morphology was observed when tips of young hyphae were cultured in conditions favouring fermentation. The budding cells obtained were indistinguishable from yeast-like cells generated by anaerobic germination of spores.

SUMMARY Mycotypha africana and four strains of Mycotypha microspora were studied. The former displayed total conversion from mycelium (M) to yeast (Y) when grown under N2 or in the presence of some electron-transport inhibitors with either glucose, fructose or mannose as carbon source. In air, mixed filamentous and yeast-like forms were frequently observed. Acid pH, high temperature, dense inoculum and high hexose level increased the proportion of the Y-form. Yeast and mycelial phases were interconvertible. All but one strains of M. microspora tested displayed similar dimorphism, but strain to strain variations were observed.

SUMMARY Increases in turbidity of Escherichia colistrain k12 due to added non-permeant salts (NaCl and MgCl2) and sucrose are strictly dependent on medium osmotic pressure, when correction is made for changes in medium refractive index. The volume of the whole cell and the fraction of the intact cell bounded by the cytoplasmic membrane have been measured by dextran and [14C]sucrose exclusion spaces. Increases in medium osmotic pressure due to non-penetrant medium solutes cause outflow of water across the cytoplasmic membrane and contraction away from the cell wall (plasmolysis), corresponding to the increases in turbidity.

In addition salts (NaCl and MgCl2) cause appreciable contraction in volume of the whole cell, presumably due to ionic interaction with the wall; sucrose causes only marginal decreases in whole cell volume. Electron micrographs of cells plasmo- lysed by NaCl or MgCl2, but not by sucrose, show numerous adhesion points between the wall and the cytoplasmic membrane.

Glycerol penetrates the cell to the same extent as water, but because of its slower rate of penetration, transient decreases in volume occur which can be measured in a stopped-flow spectrophotometer due to concomitant increases in turbidity. In cells grown on glucose-containing medium the rate of glycerol penetration is non-saturating. In cells grown on glycerol an additional saturating- facilitated diffusion system is induced. Mutants deleted in the facilitator (F−) are available and do not show facilitated diffusion when grown on glycerol. Water exit and glycerol penetration in glucose-grown cells show transition points in Arrhenius plots corresponding to phase changes of the membrane lipids.

Summary: A lysine bradytroph of Penicillium chrysogenum Wis. 54–1255 was isolated. The mutant (l1) grew with α-aminoadipic acid and excreted homocitrate. In vivo accumulation of homocitrate, which did not require protein synthesis, was markedly reduced by lysine. These results indicate that lysine diminution of penicillin production is caused by feedback inhibition of homocitrate synthase, thus limiting the supply of α-aminoadipic acid available for penicillin biosynthesis.

Summary: When a culture of a sensitive yeast strain is treated with yeast killer-protein, there is an increase in turbidity. This killer protein-induced turbidity increase coincides with the loss of cellular ATP, and appears to be caused by increased light scattering owing to a reduction in volume of the treated yeast cells. Sphaeroplasts prepared from sensitive cells were also sensitive to killer protein, and a culture showed a large increase in turbidity when treated with killer protein. The increase in turbidity of sphaeroplasts was not accounted for by a change in volume, but did correlate with killer protein-induced alterations in membrane permeability, and is consistent with a killer protein-induced alteration in light scattering of the yeast cell membrane.

Summary: Prolonged blue-light irradiation was necessary for almost total reversal of sporulation in Botrytis cinerea Pers. ex Fr. Studies of blue-light exposures of various durations during the dark period after photoinduction showed that there were two phases of maximum sensitivity to blue light, namely between 12 and 16 h, and between 20 and 24 h after the end of photoinduction. A brief exposure of 15 min to blue light (250 µW/cm2) at the 12th hour after the end of photoinduction brought about 20 % suppression of sporulation. The inhibition response was saturated at the 60 % inhibition level with more than 6 h blue-light irradiation. Blue light arrested spore formation and then caused de-differentiation of conidiophores to sterile mycelia.