- Volume 31, Issue 3, 1963

Spontaneous mutations, and those induced by nitrous acid or ultraviolet light, were studied in the haploid fission yeast Schizosaccharomyces pombe. Reverse mutations conferring ability to grow on a minimal medium lacking adenine were scored in adenine auxotrophs, and in di-auxotrophs having requirements for both adenine and methionine. The apparently lower mutability of the ad-1 mutants in the ad - met - diauxotrophic strains compared with the ad - strains was shown to be due to the influence of methionine in the plating medium. L-methionine added to the minimal medium at a concentration of 40 μg. per ml. will suppress the appearance of spontaneous and induced revertants of adenine-1 mutants. A similar effect has been shown for reversions of an adenine mutant at another locus, and for reversions of a leucine auxotroph. Methionine has the effect of decreasing the extent of residual divisions undergone by adenine-requiring cells when plated on a minimal medium.

A non-precipitating chemically defined medium containing lactate, sulphate and other inorganic salts supported repeated subculture of Desulfovibrio desulfuricans, strain Hildenborough; yields of bacteria were comparable with those obtained in media containing yeast extract or peptone. Addition of yeast extract, amino acid mixtures or ATP to the defined medium increased the crop. Growth on other organic substances was poorer than on lactate; amino acids were less efficient nitrogen sources than ammonia. Pyruvate served as electron acceptor for hydrogen uptake by resting organisms but did not support growth in sulphate-free medium.

Although tetanus toxin is fixed by brain ganglioside, it is not fixed by a number of substances more or less closely related to brain ganglioside, or by naturally occurring brain ganglioside not containing hexosamine, or by a hexosamine-containing ganglioside from Tay-Sachs brain. Isolated brain gangliosides may vary considerably in their toxin-fixing capacities. In chloroform + methanol extracts of brain a number of gangliosides which differ in ability to fix toxin can be separated chromatographically. Complexes of ganglioside with phrenosine and sphingomyelin have diminished toxin-fixing capacity. Tetanus toxin and ganglioside have a high binding capacity for calcium, but calcium does not affect the fixation of toxin by ganglioside. Ganglioside fixes strychnine, brucine and thebaine, drugs which have the same neurophysiological activity as tetanus toxin. Ganglioside does not fix γ-aminobutyric acid, β-hydroxy-γ-aminobutyric acid, histamine, adrenaline, noradrenaline or dopamine, but it does fix serotonin and a number of related compounds. It has been confirmed that albumin is fixed to a small extent by ganglioside at low salt concentration, but (unlike tetanus toxin) this fixation is practically abolished at physiological salt concentration.

The apparent non-fixation of tetanus toxin by frog brain emulsion has been re-examined. Frog brain emulsion does fix tetanus toxin, but only with 1/2000th the capacity of mammalian brain emulsion. This low toxinfixing capacity may be connected with the observation that the ganglioside in frog brain, unlike that in mammalian brain, is extractable with aqueous solvents.

The motile spore of the water fungus, Blastocladiella emersonii, contains a single, large, posterior, eccentrically disposed mitochondrion; some 6–12 prominent, strongly osmiophilic, lipid-like organelles, bordered by a double membrane, occur along its outer edge. A single flagellum with the classical 9-plus-2 fibrillar structure is attached by at least one banded rootlet to the mitochondrion. The nuclear cap (a package of ribosomes) overlies the nucleus and is separated from it by a double membrane. The cytoplasm is somewhat granular, contains structures believed to be organelles (previously described as γ particles), but is devoid of any obvious cytoplasmic reticulum. Before spore germination, the flagellum undergoes a series of characteristic movements. Following this, the nuclear apparatus rotates through some 270°, but the spore itself does not turn. The flagellum is then retracted into the cell. Subsequently, the spore germinates by formation of a germ tube and the nuclear cap disintegrates.

The effect of chemical sensitizing and protective agents on the rate of mutation induction by gamma radiation in strain WP2 of Escherichia coli B/r was studied. This organism will not grow in the absence of tryptophan but it mutates spontaneously at a very low rate, and under the influence of radiation at a much higher rate, to stable forms which can grow in the absence of tryptophan. Both inactivation and mutation-induction were apparently related to radiation dose by an exponential function in the absence of modifying agents; in their presence this was not always the case. The sensitizing agents oxygen and AT-ethylmaleimide, and the protective agents cysteine, glycerol, dimethyl sulphoxide and thiourea, affected both the inactivating and mutation-inducing actions of radiation though not always to the same extent.

The effect of various growth substrates on the synthesis of three inducible enzymes, the stereo-specific tartrate dehydratases, has been followed in strains of Pseudomonas. Four organic acids (succinate, malate, acetate, meso-tartrate) inhibited induction of some or of all of the tartrate dehydratases, while three (pyruvate, l-tartrate, and d-tartrate) did not inhibit. Whenever inhibition occurred, synthesis of d- and l-tartrate dehydratase was repressed much more strongly than synthesis of meso-tartrate dehydratase. Pre-induction of the bacteria did not prevent subsequent repression and a degree of correlation was found between the growth rate supported by substrates and the extent of repression. The significance of the different degrees of repression given by substrates feeding into closely related sites of the Krebs cycle and of the differences in repression exerted on enzymes acting on closely related compounds is discussed.

Two aerobic mesophilic species of a new genus belonging to the family Actinoplanaceae are described under the name Microellobosporia (M. cinerea type species). The new genus is characterized by the production of small club-shaped sporangia on the aerial mycelium. Similar stuctures are also formed on the substrate mycelium. The non-motile sporangiospores are few in number and arranged in a single straight row inside the sporangium.

Group D antisera were prepared from three culture-collection strains of Streptococcus equinus. Reciprocal absorption tests showed that they were Group D streptococci.

The detailed morphology of several new coliphages is compared with that of the more familiar types; the resulting information is considered for its taxonomic value. Some were examined at molecular level and new information on the tail structure of the ‘T even’ phages is described. It is shown that the so-called tail fibres are, in fact, the remains of a network which surrounds the extended sheath. From this information it is possible to propose the changes in molecular packing accompanying sheath contraction.

A new phage with an octahedral head and contractile tail is described. It is also shown that phage T3 almost certainly has an octahedral head. Electron micrographs of øR (a øX174 type phage) show that it consists of two parts: an icosahedral protein shell, and morphological subunits attached to each apex.

A strain of Gluconobacter liquefaciens was found to possess peritrichous flagella. Because of this and its biochemical similarity to Acetobacter aceti, the organism should be transferred to the genus Acetobacter as restricted by Leifson.

Freeze-dried spores of Bacillus megaterium, B. stearothermophilus, Clostridium bifermentans and C. botulinum type E suffered little or no loss in viability after storage at 25° at water activity (aw ) values between 0.2 and 0.8. When stored over P2O5 (0.00 aw ) the spores of all four species showed a marked loss in viability. The above results were similar for spores whether stored in air or in vacuum. With spores stored over distilled water (1.00 aw ) the Bacillus spores underwent a large loss of viability in vacuum, but not in air; for spores of the clostridia the reverse was true. The addition of DL-glyceraldehyde, diacetyl or ribose (0.05 M) to the spore suspensions before drying caused increased death during storage at 0.50 aw and to a lesser extent at 0.20 aw. Death was greater at 30° than at 10°. The addition of sucrose, glutamate or semi-carbazide did not decrease the viability. When the dried spores were resuspended in dilute phosphate buffer after storage for 2.6 years their resistance to heating was greatest after storage at aw values of 0.4, 0.6 and 0.8.

Isolates from the rumens of sheep of presumptively identified Bacteroides amylophilus, B. ruminicola, species of Bacteroides, Selenomonas, Butyrivibrio, Bacillus, Eubacterium, Clostridium and Gram-positive cocci were found to be proteolytic. Some of these strains also had exopeptidase and amidase activity, but significant deaminase activity was rare. Most of the strains preferentially utilized ammonia in synthesizing cellular constituents in media containing preformed amino acids. Few of the strains had urease activity.

Seven strains antagonistic to indicator corynebacteria on solid media were found among 100 Staphylococcus aureus strains of human origin. These inhibitory strains all gave sharply defined inhibition zones, belonged to bacteriophage type 71, and were isolated from superficial infections. They were strongly active in direct antagonism tests against all the other ‘aureus’ strains, and against some coagulase-negative staphylococci, streptococci and other Gram-positive species; Gram-negative organisms were not susceptible. S. aureus strains producing hazy inhibition zones with corynebacteria showed similar though less extensive antibacterial activity. Inhibition by both kinds of staphylococci occurred under several different environmental conditions, but not in the presence of oleic acid. The antagonistic agents were relatively heat resistant, passed readily through cellophan, and showed considerable specificity in their action.

An investigation was made into the relative merits of several media for counting salt-marsh bacteria. Although extracts of salt-marsh mud were superior to extracts of meadow soil, a nitrogenous medium, i.e. ZoBell's sea-water agar no. 2216, was apparently the least selective. For the saltmarsh muds studied, media with a salinity about the same as sea water gave the highest counts of bacteria, particularly for samples from the sali-cornietum. A possible correlation between this and the origin of the mud is discussed.

The fine structure of Pythium debaryanum Hesse differs from that of Rhizopus species and some other fungi in the abundant regularly distributed endoplasmic reticulum, the presence of typical Golgi-bodies and the irregularly tubular structure of the cristae mitochondriae. Some of these characters resemble those of some algae and the liverwort Anthoceros and the significance of this is discussed. Typical lomasomes are present.

Ultrathin sections of sporangia of the actinomycete Microellobosporia flavea were examined with an electron microscope. The sporangial wall is a thin, wrinkled membrane which seems to be an extension of the outer layer of the cell wall of the sporangiophore. A substance, probably a liquid, is located between the sporangial wall and the sporangiospores. The spores are ovoid and consist of a laminated wall in which two layers can be differentiated. The wall is 30–40 mμ thick but thickens to 90–120 mμ at the point of contact between two spores. Inside the spores one can differentiate a finely granular nucleus, large vacuoles which are probably filled with a fatty substance, and a coarsely granular cytoplasm. The cytology of the sporangiospores of M. flavea is similar to that of the conidia of Waksmania rosea.