- Volume 136, Issue 11, 1990

A yeast strain highly resistant to propargylglycine (an inhibitor of cystathionine γ-lyase) was isolated from air. It was partially characterized, but it has not been identified with any known yeast species. Its sulphur amino acid metabolism differed from that of other fungi by the lack of the reverse transsulphuration pathway from methionine to cysteine, as no activity of cystathionine β-synthase or cystathionine γ-lyase was found. The functional lack of this pathway was confirmed by growth tests and by experiments with [35S]methionine. In contrast to Saccharomyces cerevisiae neither homocysteine synthase nor the sulphate assimilation pathway were repressible by methionine in the new strain; on the contrary, a regulatory effect of cysteine was observed.

Exposure of dark-grown mycelia of Trichoderma viride to white light elicited a transient burst of respiratory activity manifested as increased O2 consumption which was not paralleled by a corresponding increase in CO2 production. The period of increased uptake of O2 lasted for 5–10 min and was independent of the duration of illumination. The inhibitors of respiration tested, antimycin A and mucidin, and the antioxidant, dithiothreitol, effectively suppressed the photostimulated uptake of O2, whereas rotenone, amytal and salicylhydroxamic acid were without effect. It is concluded that the illumination of mycelia caused irreversible photo-oxidation of an as yet unidentified compound, and that the electrons released by the photochemical event were accepted by a NAD-independent flavin dehydrogenase and further transferred to atmospheric O2 via the cytochrome electron-transport chain coupled with the formation of ATP.

The production of the pigments actinorhodin and undecylprodigiosin by Streptomyces coelicolor A3(2) was examined in a chemically defined medium which permits dispersed growth of the organism. The physiological controls on the production of the two pigments were markedly disparate. Actinorhodin production occurred mainly in the stationary phase of batch cultures grown with glucose and sodium nitrate as the principal carbon and nitrogen sources. In the same batch cultures, undecylprodigiosin accumulated during the exponential growth phase. The production of both pigments was sensitive to the levels of ammonium and phosphate in the medium. Actinorhodin production was exquisitely sensitive to ammonium concentration, and was completely inhibited by as little as 1 mm-ammonium chloride, whereas more than 50 mm-ammonium chloride was required to prevent undecylprodigiosin production. A similar, but less extreme effect was seen with phosphate: actinorhodin production was completely inhibited by 24 mm-phosphate, whereas undecylprodigiosin was still formed at this high phosphate concentration. The effects of ammonium inhibition of pigmented antibiotic production were relieved by reducing the concentration of phosphate in the medium, but changing the ammonium concentration had no effect on phosphate inhibition. Thus the regulation of pigment production by these two nutrients is interrelated, with phosphate control being epistatic to that of ammonium. The results implicate a phosphorylated intermediate as a major regulator of secondary metabolite synthesis by S. coelicolor.

Azoverdin, a visible yellow, blue-white fluorescent compound produced by iron-limited Azomonas macrocytogenes ATCC 12334, was isolated from cell-free culture supernatant fluid and purified in the ferrated form to 98% purity by ion-exchange chromatography and reverse-phase high-performance liquid chromatography, thereby separating it from several related iron-binding fluorescent compounds. Purified ferrated azoverdin exhibited a pH-independent absorption spectrum which became pH-dependent following deferration, typical of a pyoverdin-like siderophore. Azoverdin enhanced 55Fe3+ assimilation by iron-limited A. macrocytogenes and therefore functioned as a siderophore. Iron-limited cells were unable to produce azoverdin when grown at 34 °C rather than 28 °C. However, these cells still expressed a 74 kDa and a 70 kDa iron-repressible outer membrane protein and were capable of azoverdin-mediated iron transport. The use of A. macrocytogenes cells grown at 34 °C eliminated endogenous azoverdin production during iron uptake assays, which made it possible to accurately determine azoverdin-mediated 55Fe3+ transport rates. Azoverdin-mediated 55Fe-uptake proceeded with an apparent K m of 0·2 μm and a V of 0·46 ng Fe3+ (108 cells)−1 min−1.