- Volume 91, Issue 1, 1975

Summary: The oxidation of carbon monoxide and methane by suspensions and ultrasonic extracts of Pseudomonas methanica was studied. A continuous assay for the oxidation of CO to CO2 was devised, using O2 and CO2 electrodes in combination. Stoicheiometries of CO-dependent CO2 formation, O2 consumption and NADH oxidation, and the partial stoicheiometries of methane-dependent NADH oxidation, suggest the involvement of a mono-oxygenase in these oxidations. Evidence is presented suggesting methane and CO oxidation are catalysed by a single enzyme system, distinct, at least in part, from the NADH oxidase present in extracts. Ethanol was able to provide the reductant necessary for CO oxidation by cell suspensions, though the metabolism of ethanol by P. methanica was found unlikely to result in substrate-level formation of NADH; the means whereby alcohol oxidation could supply reductant for the mono-oxygenase are discussed.

Summary: A mutation in a gene designated gmdA has been found to lead to loss of ability of Aspergillus nidulans to use benzamide, phenylacetamide and several other amides as sole nitrogen sources for growth. The gmdAI lesion results in low levels of an enzyme, called the general amidase, which has activity for a wide range of amide substrates. This enzyme is repressed by certain nitrogen-containing metabolites, including ammonium, but is probably not regulated by induction or by carbon catabolite repression. Evidence is presented for the general amidase being distinct from the previously characterized acetamidase and formamidase enzymes. The data also indicate that there is a fourth amidase capable of the hydrolysis of valeramide and hexanamide.

Summary: Mitochondrial structure in yeast cells under various physiological conditions has been studied by high voltage electron microscopy of sections that are 0·5 to 2·0 μm thick. Such thick sections of the yeast Candida utilis had a small number of long, branched tubular mitochondria per cell. The mitochondria extended into cell buds and unseparated daughter cells. It was apparent from parallel studies with thin sections that most of the rounded mitochondrial profiles viewed in thin sections should not be interpreted as being numerous small individual mitochondria. Attempts to study thick sections of the yeasts Saccharomyces cerevisiae and Schizossaccharomyces pombe were frustrated by poor contrast.

SUMMARY: Nine volatile hydrocarbons, as well as methyl chloride, carbonyl sulphide and carbon disulphide, have been identified by mass spectrometry as products of Agaricus bisporus in the compost used in commercial mushroom beds. Of these, only ethylene showed a pattern of production that could be correlated with developmental phases of the crop, high levels being produced whenever fruit bodies were rapidly enlarging.

In laboratory flask cultures, under controlled conditions, high levels of ethylene occurred whenever young fruit bodies entered the expansion phase. The enhanced rate of ethylene production continued over several days, irrespective of whether fruit bodies were removed. Production occurred within the colonized compost; no ethylene was evolved by the fruit body itself.

When the first fruit bodies expanded, either in beds or culture flasks, laccase levels in the compost fell and those of a β-1-1,4-glucanase (cellulase) rose. The enzyme switch occurred once only, during maturation of the first fruit bodies, whereas an elevated ethylene production was associated with each occasion when fruit body maturation took place.

The low level of laccase and high level of cellulase characterized the whole of the reproductive stage of A. bisporus, whereas the phasic periods of high ethylene production distinguished between periods of fruit body maturation and intervening resting periods.

Summary: Stable auxotrophic mutants were induced in Humicola sp. strain 20–31 by irradiation with far ultraviolet light. Mixed inoculation of different auxotrophs on to minimal medium agar produced prototrophic mycelia in all seven combinations tested with a frequency of 0·5 to 2·5%. These prototrophic mycelia were stable when subcultured by macerated hyphae, single hyphal tips, single aleurio-spores or single phialospores, and contained nuclei of approximately twice the volume of those in strain 20–31. They were more sensitive to growth inhibition by p-fluorophenylalanine (FPA) than 20–31 and its auxotrophic derivatives and, at concentrations of 140 and 160 μg FPA/ml, gave rise to more vigorously growing sectors. The mycelia from these sectors segregated for morphological and auxotrophic markers differentiating the parent auxotrophs and contained nuclei similar in size to strain 20–31. When reinoculated on to FPA media, these segregants showed the higher tolerance characteristic of strain 20–31 and failed to segregate further. It is concluded that in mixed culture, auxotrophic mutant derivatives of Humicola sp. strain 20–31 readily form somatic heterozygous diploids and that these are induced to haploidize by treatment with FPA. A difference in pigmentation which segregates spontaneously in strain 20–31 is attributed to a single chromosomal gene and the six markers studied are assigned to at least four linkage groups. Parasexual genetic analysis may be of value in taxonomic studies of imperfect fungi.

Summary: DNA was isolated from 19 strains and substrains of Streptococcus sanguis and analysed for guanine plus cytosine (GC) contents and base sequence homologies. Three groups could be discerned: group 1 strains had 40·8 to 42·8 mol% GC; group 2, 42·7 to 44·0 mol% GC; group 3, 43·8 to 46·4 mol% GC. DNA homologies between groups 1 and 3 were 40 to 60% at 67°C and 40% at 72°C. The homologies of group 2 towards groups 1 and 3 were much lower. Strains in groups 1 and 3 hydrolysed arginine and aesculin and fermented inulin; group 2 strains did not. Groups 1 and 3 could be considered subspecies of S. sanguis. Group 2 should not be considered S. sanguis.

Summary: For the mapping of HI, the structural gene for phase-1 flagellin in Salmonella, spontaneous non-flagellate HI mutants were isolated from a phase-1 stable derivative, SJ925 HI-g1g2g3t, of Salmonella abortusequi. First, mapping was carried out with the deletion mutants among them by P22 phage-mediated transduction. Mutants of flaA1 and flaL, adjoining opposite sides of HI, were also included in the mapping. As the result, HI was divided into 16 segments by 15 deletions. Mapping by recombination frequencies was then carried out using representative HI mutants. Comparison of the two maps showed that 14 consecutive segments near flaL covered about 70% of the non-flagellate HI mutational sites, although they were confined to a quarter of HI in the recombination map. The other two segments were found to occupy the remaining three quarters of HI. By use of the deletion map, the sites of three phase-1 curly and three ah1 mutations were determined. The curly mutational sites were mapped in the segment second from the flaA1 side and the ahi mutational sites in the segments near the flaL side. To ascertain approximate positions of the areas determining the phase-1 antigen specificities, their arrangement relative to a curly mutational site, curly-2, and HI-linked fla genes was examined by three-point crosses. From the results, all the antigenic specificity-determining areas examined were located between flaA1 and curly-2 in the following order: flaA1--g2-g1-g4-(g3,g5,f,m,t)-curly-2---flaL.

SUMMARY: A procedure to enrich for auxotrophic and fermentation mutants of Agrobacterium tumefaciens is described. The method is based on the amplification of the killing power of carbenicillin by the addition of lysozyme. Isolation frequencies of some types of mutants are presented, with and without the application of the proposed procedure. The yield of mutants is usually enhanced a hundredfold per enrichment treatment.

Summary: The activities of polymyxin B sulphate, colistin (polymyxin E) sulphate and their sulphomethyl derivatives were compared by continuous turbidimetric monitoring of dense cultures of an Escherichia coli strain exposed to these agents. Judged by the concentration of antibiotic which caused a rapid fall in opacity of the culture, polymyxin B sulphate and colistin sulphate had similar activities, but the sulphomethyl compounds differed considerably: sulphomyxin sodium induced lysis of the culture at a concentration four times that of the parent compound, whereas colistin sulphomethate sodium induced a delayed fall in opacity consistent with recruitment of activity as the inactive sulphomethyl derivative was broken down to the parent compound.

During overnight incubation, regrowth of cultures which had initially succumbed to polymyxin action occurred, apparently due to the selection of phenotypically resistant variants from within the population. In this way cultures could easily be adapted to growth in concentrations of antibiotic well above the conventionally-determined minimum inhibitory concentration. The comparative ease of adaptation was in the order: colistin sulphomethate > sulphomyxin > colistin sulphate > polymyxin B sulphate.

SUMMARY: There is a major reduction in respiratory competence, and inhibition of growth, several hours after the addition of erythromycin or chloramphenicol to Saccharomyces cerevisiae growing in medium containing a non-fermentable carbon source. Spectrographic evidence is presented for a loss of cytochrome oxidase as a consequence of the antibiotic treatment. This loss is prevented by cyanide or oligomycin. When glucose is added, however, the loss occurs irrespective of the presence of the respirator inhibitors. Cycloheximide does not affect respiratory competence or cause loss of cytochrome oxidase, and it prevents the loss elicited by erythromycin if both compounds are added together. However, if cycloheximide is added some time after the addition of erythromycin, it fails to block the response to the latter drug. The results cannot be accounted for on the basis of the segregation of a finite number of mitochondria into an increasing number of progeny cells but, rather, suggest that the mitochondria are modified during growth in chloramphenicol or erythromycin.