- Volume 117, Issue 2, 1980

A spectrofluorometric assay for the estimation of the tremorgenic mycotoxin verruculogen in crude mycelial extract has been devised and used to determine concentrations as low as 0·2 μg ml−1. Verruculogen production by Penicillium estinogenum has been extended from surface culture to submerged culture in 60 1 stirred fermenters, in which the maximum cell-associated mycotoxin yield [5 mg (100 ml culture)−1] was obtained within 7 d. It was found necessary to supplement the medium (Czapek Dox broth plus 0·5 % yeast extract) with calcium chloride (2 %) to induce profuse sporulation (2 × 107 conidia ml−1).

Asparaginase II activity in Saccharomyces cerevisiae can be derepressed in stationary phase cells by nitrogen starvation in the presence of an energy source. We have found that high activity of this enzyme is present in early-exponential phase cells even in the presence of abundant nitrogen. In growing cells that contain high asparaginase II activity, further derepression by nitrogen results in the rapid appearance of additional activity. Rapid loss of activity occurs as cultures begin to emerge from exponential growth. Synthesis of protein is required just before loss of activity occurs. Supplementing cultures with l-asparagine or l-glutamine strongly affects the kinetics of loss of activity. Mutation in ASP2 or ASP3, which results in inability to derepress this enzyme in stationary phase cells, also prohibits the development of the enzyme in exponentially growing cells.

The metabolism of Rhizopus arrhizus (Fischer) during growth and asexual sporulation was investigated. Aerobic respiration occurred during spore germination but changed to fermentation during the initial stages of growth. During the later stages of growth and sporulation, the respiration again became aerobic. The fermentative phase during the initial growth stage was a result of culture technique. Sporulation was induced by glucose exhaustion. Protein was the major endogenous substrate during sporulation. Lipid reserves decreased, but non-structural carbohydrate reserves remained unchanged. The fermentation acids, over half of which were taken up from the culture medium, were the major exogenous substrate during sporulation. Lactate was identified as one of two fermentation acids produced in significant quantities. On a weight consumed basis, the fermentation acids were the major substrates utilized during sporulation.

Lactate, ethanol and butanediol were excreted when Alcaligenes eutrophus was exposed to severely restricted aeration. This indicated the presence of dehydrogenases which are not normally present in aerobically grown cultures of this strictly aerobic bacterium. When grown in the presence of measurable dissolved oxygen concentrations. A. eutrophus strain N9A and a double mutant defective in the formation of poly-3-hydroxybutanoic acid and in the utilization of 3-hydroxybutanoate did not synthesize alcohol, lactate or butanediol dehydrogenases. However, when bacteria were subsequently incubated for 10 to 25 h under restricted aeration conditions that permitted respiration rates of only about 3 to 15% of the maximum value, the above enzymes were formed with specific activities up to 0·75 μmol min−1 (mg protein)−1. The identity of metabolites excreted as well as the nature of the enzymes formed could be correlated with the distinctive relative respiration rates enforced on the bacteria during incubation.

The results indicate that A. eutrophus contains genetic information which is not expressed under ordinary cultural conditions. The significance for retention of the dormant genetic material in strictly aerobic bacteria is discussed.

Phenotypic resistance to both amphotericin B and miconazole develops in stationary phase cultures of Candida albicans and this resistance lies in changes in the cell wall. Study of the effects of growth conditions, treatment with SH-reactive agents and treatment with enzymes indicates that the nature of the changes leading to resistance must be different for the two drugs.

Mutants of Pseudomonas aeruginosa PAC1 which could grow on l-threonine were isolated. These mutants, like the parent strain, synthesized a biosynthetic threonine deaminase, but its apparent K m value for threonine was higher than that of the enzyme from strain PAC1. These mutants also synthesized an inducible NAD-dependent threonine dehydrogenase, which was not present in the parent strain. No threonine aldolase activity could be detected. The results suggest that the threonine deaminase with lowered affinity for l-threonine, together with l-threonine dehydrogenase, enabled these mutants to utilize l-threonine as the sole source of carbon for growth.

When sporulation was induced in batch cultures of N2-fixing Clostridium pasteurianum, either by adding calcium acetate or by increasing the pH, inactivation of glutamate synthase, partial inactivation of nitrogenase and excretion of NH4 + were observed. Glutamine synthetase activity remained unchanged during sporulation.

A filamentous phage- PR64FS, which adsorbs to tips of I pili was isolated. PR64FS is shorter than the I pilus-adsorbing phage If1 and differs from it in plaque morphology. Phages PR64FS and If1 are serologically related and, like the latter, PR64FS adsorbs to pili coded by all Inc groups of the I plasmid complex.

Esterases of 57 strains of Shigella dysenteriae, Sh. flexneri, Sh. boydii and Sh. sonnei and 26 strains of Escherichia coli, including the Alkalescens Dispar group, were compared by polyacrylamide-agarose gel electrophoresis. Six types of esterase bands differing in their ability to hydrolyse synthetic substrates and in their sensitivity to heat and to di-isofluoropropyl phosphate were defined. Individual activities and sensitivities of these bands and the apparent molecular weight of the major esterase, estimated to be 58000 by polyacrylamide gradient gel electrophoresis, were identical for both Shigella species and E. coli. One esterase with a molecular weight of 104000 was found in some strains of E. coli. Variations in the number and mobility of bands among Shigella strains defined different esterase patterns (zymotypes) which appeared to be distinct for each species.