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Summary: We have compared the effect of diphenylamine (DPA) on the pigment composition of Rhodopseudomonas sphaeroides f. sp. denitrificans grown in photoheterotrophic culture with the previously reported effect of nitrate. It was demonstrated that the effect of nitrate is due to the nitrite which is produced during denitrification. Both nitrite and DPA caused a decrease in the synthesis of spheroidene, and the accumulation of more-reduced precursors not normally seen. Nitrate (effectively nitrite) caused a decrease in the amount of bacteriochlorophyll, and the reaction centre from denitrifying cells did not contain the 28 kDal polypeptide (RC-H) subunit. These effects did not occur over a range of DPA additions (4 to 8 μ;g ml-1) to cells growing in the absence of nitrate. Denitrifying cells also had 40-50% lower activity of δ-aminolaevulinic acid synthase than those grown with or without DPA. Both nitrite and DPA treatments resulted in the loss of the B870 light-harvesting complex because of a failure to synthesize its 12 kDal polypeptide subunit.

Forty cysteine-requiring mutants of Paracoccus denitrificans were isolated. The growth requirements of these mutants were consistent with sulphite and sulphide being intermediates in the reduction of sulphate to cysteine in P. denitrificans. Fourteen were deficient in ATP sulphurylase and/or APS kinase. Of these, twelve were also unable to transport sulphate into the cell, showing that they were pleiotropic, being deficient in at least two and possibly three enzymes of the cysteine biosynthetic pathway.

The metabolic pathway for the reduction and incorporation of sulphate in Paracoccus denitrificans strain NCIB 8944 has been elucidated and the control and regulation of the pathway is reported. Several enzymes of the sulphate metabolic pathway have been assayed in P. denitrificans grown on different substrates. In addition, several enzymes have been purified and in vitro inhibitor studies conducted on them. Cysteine plays a primary role in the control of sulphur metabolism in P. denitrificans.

Summary: Metabolic profiles from four stages of differentiation of the fungus Phytophthora palmivora were obtained by gas chromatography/mass spectrometry. The profiles showed the presence of sterols in the asexual reproduction stage of the organism, and confirmed their virtual absence from the mycelial stages. The zoospore stage was characterized by the presence of polyunsaturated fatty acids of C20 and C22 chain length. The transition from zoospore to cyst was also marked by the appearance of disaccharides and by a decrease in the amount of phosphate present. There were also distinctive shifts in the proportions and the total amounts of amino acids present, with γ-aminobutyrate and alanine increasing as germination took place. These distinctive profiles identify some of the metabolic changes which accompany differentiation in this fungus.

SUMMARY: A spectrophotometric technique is described by which uptake of 2-chloromercuri-4-nitrophenol (CMNP), an organomercurial compound toxic to fungi, may be continuously monitored for 30 min periods. The method is demonstrated using mercury-resistant and mercury-susceptible isolates of Penicillium expansum and Cladosporium cladosporioides. With P. expansum no consistent differences in uptake were recorded. Mercury-resistant isolates of C. cladosporioides consistently absorbed less CMNP into their hyphae than did mercury-susceptible isolates.