- Volume 16, Issue 3, 1957

SUMMARY: A strain of Bacillus megaterium has been found under certain conditions to liberate a bacteriocin-like agent which has been termed ‘megacin’. The conditions necessary for induction of megacin formation in this strain are reminiscent of those leading to induction of bacteriophage in other (lysogenic) strains of the same species. Megacin, however, differs from bacteriophage in not giving rise to any further production of antibacterial principle, after acting on bacterial cells. Induction of megacin formation by ultraviolet irradiation is dependent on the composition of the medium. Only in a complete medium is megacin produced, although certain preliminary stages in the induction process and a concomitant, reversible photobiological effect can take place in minimal nutrient medium.

SUMMARY: An examination was made of the effect of certain amino acids on the growth of three isolates of Ophiobolus graminis Sacc. and of six isolates of O. graminis var. avenae, either as sole sources of nitrogen, or as supplements to ammonium nitrate. In all cases growth with aspartic acid was equal or nearly equal to that obtained with hydrolysed casein. Lysine and threonine were strongly inhibitory. The two varieties differ from each other in their reaction to cystine and cysteine, O. graminis itself making as good growth with these amino acids as with hydrolysed casein, and var. avenae being inhibited in growth.

SUMMARY: Cultures of the fungus Zygorrhynchus moelleri were grown in a glucose- acetate + ammonia + salts medium in the presence of either radioactive carbon dioxide, or acetate labelled in either the methyl- or the carboxyl-positions. After growth the protein was hydrolysed and the pattern of incorporation of radiocarbon into the amino acids was determined by chromatography and radioautography; activity from carbon dioxide appeared in glutamic and aspartic acids, methionine, threonine, isoleucine, proline and arginine. With labelled acetate lysine and leucine were also radioactive. A pool of free amino acids was present in this fungus.

Several amino acids were isolated from the three samples of hydrolysed protein and their specific activities were determined. Assuming that the tricarboxylic acid cycle operated in this organism, a number of predictions concerning the distribution of radiocarbon in certain amino acids which could be made were largely confirmed by the experimental findings. By partial degradation of glutamic and aspartic acids, followed by assay of the radioactivity in the products, it was possible to calculate that about 60% of the oxalacetate used for citrate synthesis was recycled C4-di- carboxylic acid; 40 % was synthesized from pyruvate and carbon dioxide. Approximately 25 % of the total respiratory carbon dioxide evolved could be accounted for in terms of decarboxylations occurring within the citric acid cycle.

SUMMARY: Radioactive glucose has been supplied to starved and unstarved cells of the fungus Zygorrhynchus moelleri for short periods of time, and a partial analysis was made of the nature of those substances incorporating radiocarbon from labelled glucose. It was found that although glucose was metabolized more rapidly by unstarved cells it rapidly entered the cells in both nutritional states and was converted to a number of other substances within the first 15 sec. Differences were found in the pattern of incorporation of labelled carbon between starved and unstarved cells, suggesting that starvation resulted in a disturbance of the balance of the relative metabolic pathways utilized for glucose metabolism in unstarved cells.

In further experiments cells were prepared in four physiological states: growing, resting after growth, starved in buffer, and after metabolizing glucose for several hours subsequent to starvation. By use of substrates variously labelled with radiocarbon it was found that the extent of recycling in the tricarboxylic acid cycle, which is similar in growing and resting cells, rose considerably when the cells were starved, and remained high for several hours during the incubation of starved cells with glucose. The minimum percentage of glucose which was metabolized primarily at the Ci position rose from 11 % in growing cells to 19 % in resting cells, fell nearly to zero immediately following starvation, and increased to 5 % after some hours in the presence of glucose.

SUMMARY: In mixed cultures where Chilomonas paramecium and Tetrahymena pyriformis W were in competition for the same dissolved food, the population size of both species (expressed in terms of total number of organisms), as well as the size and shape of individual organisms, were all affected by the presence of the other species. The size of the Chilomonas population was significantly larger in mixed than in single cultures up to the stationary phase, after which the Chilomonas rapidly decreased in numbers and finally died out. The Tetrahymena population was also larger in mixed cultures in the early stages, though by the beginning of the stationary phase this was not so. Only when the Chilomonas had died out did the Tetrahymena population again reach the size of that in single cultures. In terms of total volume of organisms, the growth of the Tetrahymena population was not as good initially as in single cultures. Later, when the Chilomonas population became very small, the total volume of the Tetrahymena population increased and finally reached the size of the population in single cultures.

Chilomonas paramecium and Tetrahymena pyriformis were both more slender in mixed than in single cultures, the differences being statistically significant. Variability of the organisms was greater in mixed cultures and changed with the age of the population. During population growth, the individual size of the Chilomonas and the Tetrahymena changed; but the time-course of change was different for the two species. While the size of the Chilomonas increased in the logarithmic phase and then decreased, the size of the Tetrahymena decreased in the logarithmic phase and increased in the phase of negative growth acceleration. In old cultures, the size of both species was smaller than at the beginning of the stationary phase.

SUMMARY: Cultures of Azotobacter chroococcum isolated by four independent operators regularly produced Gram-positive forms, from which typical cultures of A. chroococcum were recovered under controlled conditions. This observation appears to confirm those of earlier workers, and is in accordance with the theory that the aerobic and anaerobic nitrogen-fixing bacteria may be closely related.

SUMMARY: The formation of pyocyanine by resting Pseudomonas aeruginosa was studied. Glutamic acid was found to be a good substrate for this synthesis and could be replaced by several related amino acids (γ-aminobutyric acid, pyrrolidone- carboxylic acid, glutamine, aspartic acid, proline, hydroxy proline, arginine, histidine, alanine), and by some organic acids active in the tricarboxylic acid cycle (succinate, fumarate, pyruvate) when added together with ammonium ions. Magnesium ions were essential for pyocyanine synthesis and could not be replaced by other metals tested (Co, Fe). Pyocyanine formation was inhibited specifically by respiratory poisons (KCN, NaN3); NaF, on the other hand, was not inhibitory.

SUMMARY: A powerful lytic factor has been obtained in phage lysates of group C streptococci, which is active against streptococci of groups A, C and E and under some conditions group H. It is the factor responsible for ‘nascent’ phage lysis. The lytic activity remains unaltered by the removal of the phage by high-speed centrifuging, and also in the presence of phage antiserum. It is active against young and old cell suspensions, live, or killed by chloroform. The activity diminishes in the absence of reducing agents and it is destroyed by proteolytic enzymes. Heat-killed cocci when attacked by the lytic factor become Gram-negative but do not lyse. The addition of a proteolytic enzyme completes lysis. Efforts to demonstrate the release of proteinases from streptococcal suspensions have failed. After lysis the group polysaccharide is free as a hapten and some cell-wall structure remains. M antigen is also present in group A lysates.

SUMMARY: When known volumes of wet Desulphovibrio desulphuricans were suspended in standard NaCl solutions, the chloride was not diluted by intracellular water below 3 % (w/v) NaCl; at 4 and 6 % NaCl exchange occurred but not to the extent observed when the organisms were made permeable with cetyltrimethyl- ammonium chloride (CTAC). With intact organisms Na2SO4 up to 15 % (w/v) was not diluted by intracellular water. Dilution of 4 and 6 % NaCl was due to plasmo- lytic dehydration of organisms rather than to osmotic breakdown, since phosphate, cytochrome c 3 and 265 mμ.-absorbing material did not escape from the organisms, though they did with CTAC; plasmolysis was not visible microscopically. Hence these sulphate-reducing bacteria are freely permeable neither to chloride nor sulphate. Data on bacterial dimensions and fluid contents derived from this work are recorded; they compare satisfactorily with those obtained by optical measurements.

SUMMARY: Cephalosporin C, a hydrophilic, penicillin-like antibiotic which is insensitive to penicillinase, is much less active than benzylpenicillin against the Oxford strain of Staphylococcus aureus but much more active than benzylpenicillin against a penicillinase-producing strain of S. aureus (D3R). When used together, cephalosporin C and benzylpenicillin act synergistically against S. aureus strain D3R in vitro, presumably because cephalosporin C is a competitive inhibitor of penicillinase. When grown under certain conditions in the presence of cephalosporin C, benzylpenicillin, or bacitracin, the Oxford staphylococcus gives rise during a single culture to a resistant bacterial population consisting largely or partly of Gram-negative bacilli. In the presence of bacitracin a similar change also occurs with S. aureus strain D3R.

SUMMARY:Gram-negative bacilli were obtained from the Oxford strain of Staphylococcus aureus in the presence of benzylpenicillin, and single organisms were isolated from these bacilli. The properties of bacilli derived from the isolates were compared with those of the parent staphylococci. The two types of organism differed strikingly in morphology, staining and various biochemical reactions. The bacilli were much more resistant to benzylpenicillin than the parent staphylococcus, but much less resistant to polymyxin. Staphylococci were recovered from all the strains of bacilli. More than half of the recovered strains resembled the original staphylococcus in all properties tested, including phage type, when first isolated. The remainder formed a somewhat heterogeneous group, differing in some properties from the parent. Later, some members of this heterogeneous group also became indistinguishable from the original staphylococcus.

SUMMARY: Homogenates of Paramecium aurelia, var. 4, stock 47.8 (sensitive), grown in axenic culture contain enzymes of the glycolytic, the citric acid cycle, and the pentosephosphate pathway. The presence of the following enzymes has been demonstrated: hexokinase, phosphoglucomutase, phosphohexoisomerase, aldolase, triosephosphate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phospho-gluconic acid dehydrogenase, pentosephosphate isomerase, citric acid oxidase, isocitric acid dehydrogenase, & α-ketoglutaric acid dehydrogenase, succinic acid oxidase, malic acid dehydrogenase, glutamic acid dehydrogenase, fumarase, and acid phosphatase. The presence of phosphorylase, transaldolase and transketolase is indicated.

Summary: The formation of macrospores in normally mycelial strains of Trichophyton mentagrophytes and T. rubrum was induced by growing the cultures in a gas phase containing air + 12–24% (v/v) CO2. When conidial transfers were made from strains which had thus been induced to form macrospores and were incubated in normal air, the subsequent growth was mycelial and downy. One strain of each fungus, normally conidial and granular, formed arthrospores under increased CO2.

SUMMARY: Semi-solid agar media prepared as previously described (Knox, 1955; Knox, Swait & Woodroffe, 1956) were found especially useful for studying the sensitivity of cultures of Mycobacterium tuberculosis to isoniazid, streptomycin and p-aminosalicylic acid (PAS). Kirchner, Fisher and Dubos media were compared both as semi-solid and as liquid media. In the semi-solid media when large inocula of M. tuberculosis H37Rv strain were used, results could be read in 2 days with a hand-lens and were usually easily read with the naked eye in 3–5 days. Results were easier to read and interpret in semi-solid than in the corresponding liquid media both because of the sharpness of the initial end-point defining the minimum inhibitory concentration of the drug (m.i.c.), and because the later growth of numerous or isolated colonies gave a measure, not obtainable with liquid media, of the variability within a culture. Such presumptively resistant colonies appeared most frequently with isoniazid in Kirchner semi-solid medium (in which the drug decayed rapidly), and less frequently with streptomycin and PAS. Colonies which appeared in iso-niazid-containing tubes were not always found to consist of drug-resistant organisms on subculture. But when 2–3 days were allowed for microcolonies to appear before the drug was added, then the few large colonies which subsequently developed were found to contain truly resistant organisms. Strains resistant to isoniazid or streptomycin were distinguished from sensitive strains more easily than in liquid media. PAS sensitivity tests gave sharp and consistent end-points in Fisher and Kirchner semi-solid agar even when large inocula were used, though the actual level of the m.i.c. varied greatly with inoculum size, and with different strains. This may be partly accounted for by the reversal of PAS by p-aminobenzoic acid (PAB). In Dubos medium readable end-points were often obtained only with small inocula. For all three drugs it seemed that Fisher semi-solid agar gave the most satisfactory results.

SUMMARY: In three independently obtained mutant strains of Aspergillus nidulans, resistant in different degrees to acriflavine, resistance is due, in each case, to mutation in a single gene. Two of the mutant alleles, ACR1 and ACR3, are semi-dominant and either allele confers a high degree of resistance. These alleles are located about 23 units distal to the w (white conidia) locus and are presumably allelic. A cross involving these two alleles in repulsion gave 0.1% sensitives. A third mutant allele (acr2) is also located on the w chromosome, but on the other arm about 25 units distal to the ad1 locus and over 100 units distant from the ACR1 and ACR3 loci. This allele, which confers relatively slight resistance, is almost completely recessive. Diploid strains which carry any allele for resistance in heterozygous condition give, by vegetative segregation, haploid and homozygous diploid resistant types which are preferentially selected on medium with acriflavine. The use of this technique for the automatic selection of vegetative segregants provides an additional tool for analyses through the parasexual cycle.

SUMMARY: A comparison of an indirect method of counting virus particles (i.e. the ‘absolute assay ’ haemagglutination method) with direct electron-microscope counts showed that the indirect method underestimated the total virus particle count by a factor of about 10. Details of technique and possible sources of error in making counts are discussed.

SUMMARY:Two of the Lactobacillus species previously defined, Lactobacillus helveticus and the ‘intermediate group ’, have been renamed L. casei var. rhamnosus and L. helveticus (Orla-Jensen) Holland, respectively. Antisera prepared against L. bulgaricus and L. helveticus (Orla-Jensen) Holland show that these species belong to the same serological group. The names of the serological groups previously defined have been replaced by letters.

SUMMARY: Particles of influenza, mumps, fowl plague, Newcastle disease and Sendai viruses were adsorbed on electron microscope films and treated with acid, trypsin and ribonuclease. All of these viruses contained trypsin-resistant rings of ribonucleoprotein and with some strains these rings showed lines of staining which may indicate the arrangement of the nucleic acid.

SUMMARY: The metabolism of methoxylated aromatic compounds by the soil fungi Haplographium sp., Hormodendrum sp. and Penicillium sp. has been investigated. A study of rates of decomposition of mono-methoxybenzoic acids by Hormodendrum sp. revealed that they are most rapidly attacked in the order para (p), meta (m) and ortho (o). In respiration studies with all three fungi the p form was again found to be metabolized most rapidly. In the initial stage of attack the methoxyl group is replaced by a hydroxyl group. Penicillium sp. also formed p-methoxyphenol from p-methoxybenzoic acid. A study of the rates of metabolism of monohydroxybenzoic acids revealed that they are attacked in the same order as the monomethoxybenzoic acids, p-Hydroxybenzoic acid formed from p-methoxybenzoic acid is further metabolized to protocatechuic acid by Hormodendrum sp. and Penicillium sp. When veratric acid (3:4-dimethoxybenzoie acid) is incubated with Hormodendrum sp. and Penicillium sp. the methoxyl group in the p position is replaced by a hydroxyl group to give vanillic acid. All three fungi formed two unidentified phenolic compounds from 2:4-dimethoxybenzoic acid. The possible significance of the results in the decomposition of lignin in soil is discussed.