- Volume 62, Issue 1, 1970

Enzymic casein hydrolysate, which is a suitable nitrogenous basis of the medium for alph-toxin production by Clostridium welchii (perfringens), was fractionated by column chromatography on Sephadex G25 gel, using ammoniacal buffer. Combined peptidic fractions were able to support microbial growth, though toxin production was minimal. Toxinogenic substances were retained on the gel and could be eluted with weak acetic acid. This active substance represented about 0·5% of the original hydrolysate and consisted of a mixture of low molecular weight peptides with free amino acids and a mineral portion (calcium, magnesium and iron). When column chromatography of enzymic casein hydrolysate was done with Sephadex G25 and 0·05 m-ammonium hydrogen carbonate buffer, toxinogenic substances were not retained on the gel. The procedure resulted in a group separation of peptides according to their molecular weight and simultaneously an adsorption effect was observed of aromatic amino acids on the gel. Four fractions were obtained exhibiting different effects on growth and toxinogenesis by C. welchii.

The fraction containing the largest molecules and the major part of total nitrogen (90% approx.) proved to stimulate microbial growth, though only minimal α-toxin production. The other three low molecular fractions exhibit a stimulating effect on α-toxin production; their amino acid compositions were different.

The most active of the low molecular weight fractions contained about 1·8% of the initial nitrogen and could be fractionated with DEAE-Sephadex A25 into a further four groups of which the most remarkable was peptide-bound tyrosine.

Gel chromatography on Sephadex columns resulted in an unequal distribution of Fe ions among the fractions; this was allowed for in performing comparative microbiological tests.

Erythrose strongly inhibits the growth of Vibrio cholerae and Vibrio eltor.The inhibition can be reversed by washing the cells free from erythrose with sterile normal saline. The respiration of V. cholerae cells in the presence of glucose is markedly inhibited by erythrose but the oxygen uptake of cell-free extract under the same conditions is not affected. From the results of experiments on the uptake of [14C] glucose and [α-14C]methylglucoside, it may be concluded that erythrose inhibits the transport of glucose across the cell membrane and thereby inhibits the growth of the organism.

SUMMARY: Seventeen fungal species from Wisconsin prairie soils were grown on Czapek nutrient media that had been treated with the insecticides aldrin, lindane, parathion, phorate or carbaryl. All five insecticides inhibited to some extent the growth of most fungal species; this inhibition was a result of a particular insecticide-fungus combination. Threshold concentrations of insecticides, at which no decrease in growth of Aspergillus fumigatus or Fusarium oxysporum occurred, differed for each insecticide and also for each of the two fungi. Since most of the insecticides had some fungicidal effect, it was not surprising that none of the 17 fungi was able to utilize any of the insecticides as a carbon or phosphorus source. Carbaryl or aldrin at 20 μg./ml. inhibited growth of F. oxysporum by 37 to 44 %. However, the addition of yeast extract, asparagine, ammonium sulphate, ammonium nitrate or ammonium sulphamate to the culture media resulted in a complete suppression of the growth inhibitory effect of carbaryl and that of aldrin to a large extent. Replacement of yeast extract with a vitamin mixture had no effect; fungal growth was still inhibited.

After starvation, yeast exposed to elevated temperatures produced CO2 twice as fast as unexposed organisms. The lag which preceded linear C02 production by starved yeast was essentially eliminated by heat treatment. Uptake and retention of sorbose was greater in heated yeast. Heating was accomplished by brief immersion of the organisms in heated solutions and by growth for 2 h. at 35°. Short heat treatments increased the production of C02 when glucose was included in the suspending medium, whereas heating in water or in growth medium without glucose resulted in a decreased production of CO2.

SUMMARY: In the hypha of Paracoccidioides brasiliensis the succinic dehydrogenase activity is localized in the mesosomes, plasma membrane and mitochondria. Short permanganate fixation after incubation enhances the positive cyto-chemical reaction. The higher activity is localized in mesosomes and it is observed as high electron-dense zones and concentric ring-like patterns.The membrane shows a spotty reaction and the mitochondrion shows a positive zone in the intracristae space.

SUMMARY: A theoretical treatment of growth and sporulation of Bacillus subtilis Marburg strain 168 in continuous culture is given. Sporulation is considered as a probability event, and a specific rate constant for its initiation in vegetative cells is introduced. The processes of growth and sporulation have been assumed to compete with each other in the vegetative organism. Equations are given which allow calculation of the rate constants characterizing growth and sporulation in steady-state continuous-flow systems. The relationship between the specific rate of initiation of sporulation and the growth rate of vegetative cells was determined with glucose-limited cultures and was approximately linear; the spore initiation rate increased with decreasing growth rate. This result was used to obtain equations relating the incidence of refractile spores to the dilution rate of a continuous culture maintained in a steady state. A number of possible models of the process of spore initiation have been considered; two were consistent with the linear relationship between spore initiation rate and growth rate determined by experiment.

To improve results obtained when examining aetinomyeetes by scanning electron microscopy, the microscope was operated under conditions giving higher resolution with a reduced but sufficient depth of focus. In addition, fixation and dehydration of specimens before coating reduced the distortion caused by desiccation under vacuum. By these means, representatives of the following genera were examined: Actinobifida, Actinoplanes, Actinopycnidium, Actinosporangium, Microbispora, Microechinospora, Microellobosporia, Planomonospora, Sporichthya, Thermoactinomyces and Thermomonospora. The study revealed points of similarity between Actinopycnidium and Actinosporangium; Microellobosporia and Microechinospora', and Actinobifida and Thermoactinomyces.

SUMMARY: Spores of several fungi were examined in an effort to understand the role of RNA in the biochemical events occurring early in germination. RNA synthesis appeared to be an essential requirement for germination in Neurospora crassa and Aspergillus nidulans but not in Alternaria solani and Peronospora tabacina. Gross changes in the relative amounts of the various molecular species of RNA were not detected during germination of P. tabacina and N. crassa spores. Pulse-labelling of the germinating spores revealed that, in N. crassa, ribosomal and soluble RNAs were the major species being synthesized, whereas in P. tabacina label was incorporated into soluble RNA and an unstable heterodisperse RNA, but apparently not into ribosomal RNA. This pattern of RNA synthesis in germinating P. tabacina spores is similar to that found in cleaving embryos of certain animals where development is also rapid and, like germinating P. tabacina spores, can occur when RNA synthesis is inhibited.

The incorporation of [1-14C]acetate into phospholipids by a toxigenic and a non-toxigenic strain of Aspergillus flavus was investigated, using a glucose salts medium (AM medium) and a sucrose yeast extract medium (YES medium) for growth and for the incorporation of radioactivity. YES medium yielded large amounts of aflatoxins. The toxigenic strain gave a higher incorporation of acetate in AM medium and a lower incorporation in YES medium than did the non-toxigenic strain. The growth and resuspension media strongly influenced the incorporation by the toxigenic strain. The specific activity obtained on AM medium was more than 10 times that on YES medium. The effects of the media on the non-toxigenic strain were less marked. The data indicate a close interrelation between the utilization of acetate for the synthesis of phospholipids and for the formation of aflatoxins.

SUMMARY: Cyanide (1 mm) strongly inhibited aerobic respiration, and 2,4 dinitrophenol (0·2 mm) apparently uncoupled oxidative phosphorylation, in nongrowing Citrobacter. At these inhibitor concentrations, anaerobic tetrathionate reductase activity was not much affected. Aeration inhibited tetrathionate reductase activity; 0·2 mm-2,4 DNP did not influence oxygen inhibition, but 1 mm-KCN restored the reductase activity quantitatively. The process of aerobic respiration rather than the oxygen molecule itself therefore inhibits tetrathionate reductase activity. Induced synthesis of reductase required anaerobic conditions. Cyanide and 2,4 DNP allowed anaerobic synthesis of reductase; aeration prevented it. This effect of oxygen was abolished neither by KCN nor by 2,4 DNP. Oxygen therefore represses the synthesis of tetrathionate reductase directly.

Rhapidosomal rods released from strain 3R of Pseudomonas fluorescens appear to be polymerized sheaths of pyocin which had a structure like that of T-even phage tails. This conclusion was based on the following observations: (1) Morphologically the rods have the same structure and diameter as the contracted sheath of R-type pyocin. (2) They resemble the poly sheath of T-even phages. (3) Antigenically they are similar to R-type pyocin. (4) They are usually induced together with R-type pyocin but not with 28-type pyocin.

Two new species of Dictyostelium, D. dimigraformum and D. laterosorum, and a new species of Acytostelium, A. ellipticum, are described. All three species were first isolated from the surface humus layer of tropical forest soils on the island of Trinidad, W.I D. dimigraformum is distinguished from other species of the genus by its ability to form both stalkless and stalked migrating pseudoplasmodia. D. laterosorum is a member of the crampon-based Dictyostelia. It differs from other members of this group in bearing lateral, sessile sori along the terminal half of the sorophore. A. ellipticum is the second species in the genus Acytostelium to be described. It is distinguished from A. leptosomum by its elliptical spores, pattern of aggregation and development, and smaller size.