- Volume 37, Issue 2, 1964

SUMMARY: After growth of Escherichia coli strain 7/9, the culture fluid and organisms contained an amino acid which gave a yellow-brown colour with ninhydrin. This compound was shown by comparison with synthetic material to be O-succinylhomoserine believed from previous work with this E. coli strain to be a methionine precursor. Its accumulation gave proof that it was formed in large amounts by the growing organisms. The formation of O-succinylhomoserine occurred equally well in the presence or absence of added homoserine and succinate, but when the succinate was added to growth media, synthesis occurred preferentially from it and the utilization of endogenously-formed succinate was diminished. Without added homoserine the extent of accumulation was such (up to 440 mg. O-succinyl-homoserine/1.) that homoserine synthesis may have been increased above normal to provide the required quantities (up to 240 mg./1.) of homoserine. Methionine completely suppressed accumulation of O-succinylhomoserine, threonine and lysine had no effect. A cystathionine-requiring mutant of Salmonella typhimurium also accumulated O-succinylhomoserine; the amount (20-30 mg./1.) being only about 5 % of that given by E. coli, and methionine prevented its accumulation by this organism too. It appears that the methionine synthesis pathway in S. typhimurium is very similar to that in E. coli and is subject to end-product control.

SUMMARY: Thirty-three strains of Pseudomonas aeruginosa, previously described as a species group by a quantitative study, were subjected to an extended schedule of tests used in bacterial classification and identification. Adansonian analysis by electronic computer confirmed previous results, indicating that the 33 strains should be treated as a species group. The 172 features coded for each strain were analysed by computer, yielding a ‘probability of occurrence’ of each feature within the species, P. aeruginosa. This output was then used to select features appropriate for diagnostic purposes. From the analyses it was also possible to measure the sensitivity of several methods for determining the presence or absence of characteristics such as pigment production and oxidation of gluconate to ketogluconate. The general applicability of the use of the computer to cooperative pooling of data by bacteriologists is discussed.

SUMMARY: Spermine oxidized by partially purified serum amine oxidase inhibited the growth of a variety of Gram-positive and Gram-negative bacteria. This inhibition of growth was not antagonized by calcium ion, and occurred over a wide pH range. Inactivation increased with time and temperature of incubation. The antibacterial action was abolished by treating oxidized spermine with sodium borohydride. Oxidized spermine inhibited protein synthesis as shown by incorporation of 14C-valine into cellular protein and by inhibition of β-galactosidase induction. Incorporation of 14C-uracil into the nucleic acids of Escherichia coli was not inhibited by oxidized spermine.

SUMMARY: The fine structure of Rhizopus rhizopodiformis was investigated. Other than a slightly modified potassium permanganate fixative, routine techniques of electron microscopy were used. The walls of the hyphae were fibrillar and electron dense. A plasmalemma, perhaps double in nature, was present. Yet to be interpreted membrane-bound vesicles were located uniformly just inside the plasmalemma. Classical ubiquitous mitochondria and smooth-surfaced endoplasmic reticulum were visible. Two inclusions, lipid and glycogen, were present. The hyphae were frequently multi-nucleated. The nuclear walls were doubled, porous, and connected with the endoplasmic reticulum.

SUMMARY: 14C-labelled Escherichia coli and other bacteria were used to measure their uptake by washed suspensions of Entodinium caudatum. All the bacteria tested were engulfed by the protozoa with a maximum uptake of 1·1 × 104 E. coli/protozoon at an initial rate of over 200 bacteria/protozoon/min. After 30 min. only 12% of the engulfed bacteria were still viable. 50% of the bacterial carbon was retained by the protozoa and, after breakage of the protozoa and centrifugation of the homogenate, 40% of this carbon was present in the supernatant fluid, principally as protein. Competition experiments where the protozoa were offered two different species of bacteria showed that the protozoa engulfed bacteria in the proportion in which they were present in the medium. The growth of E. caudatum in the presence of rice starch, autoclaved rumen fluid and penicillin was stimulated by several species of bacteria, including E. coli, Clostridium welchii, Lactobacillus casei.

SUMMARY: The multiplication of the purple photosynthetic bacterium Rhodopseudomonas palustris is inhibited by the hypocholesteraemic agents benzmalecene and triparanol. This inhibition is annulled by oleic acid, ergosterol, squalene, farnesol and lanosterol, in that order, but not by mevalonic acid, geranyl acetate, palmitic or stearic acids. Only oleic acid annuls the inhibition in higher concentrations of the inhibitors. Ergosterol and squalene, while not effective against higher concentrations of inhibitor, spared the annulment by oleic acid. An unknown interaction between oleic acid and sterols or their precursors is suggested.

SUMMARY: The hypothesis of Koch & Schaechter (1962) in its general form gives rise to mathematical relationships of great complexity. The formulae are simplified when certain conditions are met; the most important condition is that the smallest organism about to divide should not be smaller than the largest newly formed organism. Real cultures often satisfy the condition, and they can then fairly be used to test the hypothesis.

SUMMARY: Saline extracts of mouse-scrapie brain homogenates lost little infectivity when heated at 75° for one hour. At higher temperatures, there was a progressive inactivation of the agent, although some of the infectivity still remained after heating at 100° for one hour. The smooth shape of the inactivation curve suggests that the scrapie agent exists predominantly in a single heat-stable form. Ultrasonic disruption of scrapie mitochondrial suspensions altered the chromatographic behaviour of the scrapie agent in a way which suggests that the free agent is relatively small. The agent associates very readily with denatured proteinaceous material and because of this property it has not yet been possible to separate it effectively from contaminating tissue debris.

SUMMARY: The effect of multiplicity of infection on the growth kinetics of poliovirus suggests that the eclipse period usual for singly infected cells (3·6–3·8 hr) includes variable delays averaging about 1 hr. These delays are overcome at multiplicities above 3, and are sometimes spontaneously absent. They are ascribed largely to chance effects, and lead to markedly asynchronous maturation of virus; in their absence, maturation is almost synchronous.

The kinetics of acid-irreversible eclipse and of the development of antiserum resistance show that about half of the delays must occur during viral penetration; in support of this, virus growth initiated with infective RNA is 0·5 hr less delayed than that of intact virus, although otherwise similar. However, infective RNA synthesis was not detected earlier than 2 hr after infection, even in the absence of chance delays.

SUMMARY: One-step growth conditions were used in which cells began replication of poliovirus RNA almost synchronously, and in which factors limiting the rate of replication appeared to be absent. RNA of uneclipsed virus was destroyed by using light-sensitive inocula. Under these conditions, ribo-nuclease-sensitive infective RNA was detectable in unchanged amount for the first 2 hr of infection, at which time replication began abruptly; the increase of poliovirus RNA was geometrical for a further 1–2 hr.

SUMMARY: The toxicities of strains of trachoma and inclusion conjunctivitis viruses differing in virulence for the chick embryo were compared at different times during their growth in the chick embryo yolk sac. As measured by the ability to kill mice and to induce skin lesions in guinea-pigs, toxicity increased until the time at which embryos began to die. All strains possessed similar particle: toxin ratios. It is considered unlikely that the differing virulence of the strains depends on differences in the amount of toxin per elementary body.

SUMMARY: The growth in the chick embryo yolk sac of trachoma and inclusion conjunctivitis (TRIC) strains which differ in virulence for the chick embryo was measured in terms of ELD 50 inclusion forming units in HeLa cells and total particles. Observed differences in rates of growth are consistent with the assumption that greater virulence depends on a higher rate of multiplication in the chick embryo. All strains were equally labile when heated at 37° in vitro but only the more virulent kill chick embryos at 37°.

SUMMARY: Erythritol stimulated the growth of virulent strains of Brucella abortus more than that of attenuated strains. No similar correlation existed between virulence and response to erythritol with strains of B. melitensis and B. suis; these were stimulated indiscriminately by erythritol.

Erythritol was not detected in extracts of bovine white blood cells and hence is unlikely to be connected with the primary invasive process of intraphagocytic survival and growth of B. abortus. However, ultrafiltrates from extracts of bovine white blood cells stimulated the growth of B. abortus in laboratory media.

SUMMARY: Some characteristics of adenine inhibition of the rate of sorocarp formation by Dictyostelium discoideum are described. As little as 1·25 × 10−3 M-adenine was markedly inhibitory. All of the stimulants tested (histidine, glucose, Mg2+, K+, PO4 3−, Na+) were capable of stimulating the rate of fructification even in the presence of adenine, although to a lesser extent. It is concluded that the inhibition by adenine and the stimulation by the other materials listed are independent phenomena.