- Volume 8, Issue 1, 1953

SUMMARY: An organism belonging to the Pseudomonas fluorescens species-group has been isolated from fermenting cucumber by enrichment culture, using acetylcholine as the sole carbon source. This organism produces an adaptive cholinesterase.

Cells grown in tryptic digest broth have a very low cholinesterase activity. Growth for a few days in the presence of acetylcholine, choline, or Difco nutrient broth produces much higher cholinesterase levels. Cell-free preparations are also active.

The enzyme is not identical with either of the main types of animal cholinesterase. It is sensitive to prostigmine, is not inhibited by excess of substrate, and has a unique substrate specificity pattern.

The organism also produces two prostigmine-insensitive lipases, splitting triacetin and tributyrin, respectively.

SUMMARY: Under adverse conditions, Mycobacterium tuberculosis may autolyse, or surviving cells may divide into progressively shorter cells which may even appear to be coccal. We have not observed a complex ‘life cycle’, but the cells whose cytoplasm has been reduced show qualitative differences which we term ‘regression’.

SUMMARY: The log survivor/time graph for mature cultures of one strain of Streptococcus faecalis was not always straight over its whole length. A preliminary period of slow death was frequently observed, and a final similar period less often. The log survivor/time graphs of young cultures varied in shape with age of culture and often showed an initial rapid death-rate, passing suddenly into a slower one.

The heat resistance of three strains was considerably influenced by the age of the culture. Resistance, judged either by the Decimal Reduction Time or the time taken to reach 99·9% mortality, was increased by transfer to fresh medium and fell during the lag phase of growth, reaching a minimum as rapid reproduction began. A second maximum in heat resistance occurred when growth became slow: thereafter the resistance gradually fell to that of mature cultures. The incubation temperature affected the heat resistance of young cultures, the effect of high temperatures being particularly marked and resulting in increased resistance, except with cultures 1 hr. old or less.

SUMMARY: The effect of CO2 on a decarboxylase system of Streptococcus diacetilactis has been investigated. It was found that the amount of CO2 produced by a culture of the living organism depended upon the proportion of CO2 present in the atmosphere. Under minimum p CO2 the production of CO2 by the organism was stimulated while accumulation of CO2 repressed the formation of the gas. It also appeared that the presence of excess of other products of reaction repressed the production of CO2. An explanation of these phenomena in terms of the law of mass action is advanced.

The effect of CO2 upon the production of decarboxylase by the organism was also investigated. There was some indication that the composition of the gaseous environment influenced the production of decarboxylase.

SUMMARY: The rate of prototroph formation as a result of gene recombination in multiple mutants of Bacterium coli, strain K-12, is altered by addition of various chemicals to the nutrient substrate in which the recombining strains are grown. There is some correlation between the appearance of filamentous forms of the organism and the rate of gene recombination.

SUMMARY: Cytological studies upon species of Bacillus, Bacterium and Mycobacterium have shown that recent claims to demonstrate true mitotic spindles, mitochondria and fusion tubes in these genera are based upon a misinterpretation of the basophilic growing points and septa commonly found in bacteria, and a misunderstanding of the multicellular structure of Bacillus and Mycobacterium.

SUMMARY: The oxidation of ammonia to nitrite in enrichment cultures of Nitrosomonas spp. was hastened by 6 mg. Fe/1. in the medium. Manganese did not replace iron as a stimulant; it was toxic. N. europaea (Jensen’s strain) and a strain of Nitrobacter winogradskyi had, in pure culture, very small absolute requirements for iron; they oxidized ammonia and nitrite respectively in media purified with 8-hydroxyquinoline, and with no iron added. Small amounts of iron hastened the oxidation of ammonia and nitrite; the minimum concentration giving this stimulating effect was 0·1 mg. Fe/1. for the strain of Nitrosomonas europaea and 0·3 mg. Fe/1. for the strain of Nitrobacter winogradskyi. The optimum amount of iron for oxidation appeared to be about 6 mg./1. for both species. Both species tolerated 112 mg. Fe/1. (c. 0·002m), but oxidation was delayed, markedly in the case of N. winogradskyi, by 560 mg./1. (c. 0·01m).

SUMMARY: An aseptic technique is described for obtaining small hanging drops on the surface of coverslips, using only apparatus that is cheap and easy to obtain. The technique has been used to demonstrate the growth of Nocardia salmonicolor on liquid paraffin droplets.

SUMMARY: Analysis of a pair of Bacterium coli K-12 mutants which had ceased to show genetic recombination after storage, implicated mutant 58–161, which had previously behaved as a gene donor strain, as the infertile parent. Infertile 58–161 failed to display recombination when crossed with a gene acceptor strain (W-677) but was able to mate successfully with wild-type K-12 and prototrophic recombinant donor strains, i.e. it had become a gene acceptor. The terms ‘F + ’ and ‘F − ’ have been adopted (after Lederberg, Cavalli & Lederberg, 1952) to denote donor and acceptor strains respectively. Growth of either 58–161/F − or W-677/F − in mixed broth culture with 58–161/F + resulted in the conversion to F + of up to 75 % of re-isolated colonies of the initially F − strain. F − strains converted to F + by strains of dissimilar genotype showed no phenotypic alteration and, therefore, were not recombinants. Washed, mixed cultures on minimal agar yielded an F + conversion rate of only 3·6%, while 100 % recombinants were F + under the same conditions. The F + agent could be transmitted serially through F − strains and was not filterable. While F − × F − crosses were sterile, F + × F − crosses showed maximum fertility. F + × F + crosses were c. 1020 times less productive than F + × F −. The F + agent had a determining effect on the phenotype of recombinants. Thus, when the F + F − relationship was reversed in F + × F − crosses between the same pair of mutants, almost all recombinants which did not show new patterns of unselected marker characters had the phenotype of the F − parent. Among recombinants from F + × F + crosses, the phenotypes of both parents were represented though not always equally. This effect of F + on the phenotype of segregants invalidates much of the evidence for genetic linkage in K-12. Reversal of F + potential in otherwise similar crosses also had a marked effect on the efficiency of prototroph formation on minimal agar supplemented with various growth factors required by one of the parent auxotrophs. A tentative theory of the mechanism of recombination is presented on the basis of this and previous work. This supposes that F + is a non-lytic infectious agent, harboured by F + cells and absent from F − cells, which becomes effectively associated with a part (or parts) of the chromosomes of a small proportion of the cells it inhabits. The F + agent thus acts as a gene carrier in the transfer of genetic material from F + to F − cells.

SUMMARY: Incompatibility may occur in Bacterium coli strains which were previously considered homothallic. A cross between two incompatible strains is completely sterile. Such strains are termed F −. Strains which are self-compatible are termed F + and are productive when crossed either with other F + strains or with F − strains. The F + state is transmissible by infection due to a virus-like agent (F) which is not readily separable from the cells. Thus, both in vegetative and sexual reproduction, infection must be mediated by cell to cell contact. No changes other than those of compatibility have been correlated with the F + state. F is independent of λ, the latent phage of the K-12 strain of Bact. coli. A small proportion of other strains of Bact. coli are fertile when mated with K-12 and, among these, F + and F − strains are found with about equal frequency. In K-12, extreme variations in fertility are found which are only partly associated with F and partly depend on the residual genotype. The cross between two F + strains is usually less fertile than F + × F − and in such a cross one of the two strains behaves predominantly as F −, the other as F +. The F + state has a definite effect on segregation in the sense that the genetical contribution of the F + parent to the zygote, or at least to the resulting recombinants, is less than that of the F − parent.

SUMMARY: Seven strains of penicillinase-producing Staphylococcus aureus (coagulase-positive) were serially transferred on streptomycin ditchplates; four of the seven streptomycin-resistant variants showed a decreased ability to produce penicillinase. In three instances this loss in penicillinase production was caused by a decreased growth rate. The fourth strain was unstable in relation to penicillin, and exposure to streptomycin appeared to select the naturally occurring penicillin-sensitive variants.

Three of the seven strains were similarly exposed to chloramphenicol; of the three chloramphenicol-resistant variants one was slightly more resistant to penicillin, one considerably less resistant and one unchanged in relation to penicillin. The increased resistance to penicillin was associated with an increase in growth rate. The strain showing a decrease in penicillin-resistance was unstable, and chloramphenicol selected out the naturally occurring penicillin-sensitive variants.

SUMMARY: Four strains of Staphylococcus aureus (coagulase-positive) were each subjected to three or more series of transfers on penicillin ditch plates. The plates were examined for colonial variants and four quite distinct types of penicillin-resistant variant, one of which was penicillin-dependent, were isolated. These types often occurred in association, and sometimes as many as three were isolated from a single culture plate. The main characteristics of the different types are described.

Studies on the incidence of penicillin-resistant bacterial variants began soon after the isolation of the antibiotic and have continued in increasing numbers (see Abraham et al. 1941; Todd, Turner & Drew, 1945; Demerec, 1945, 1948; Bellamy & Klimek, 1948; Gale & Rodwell, 1948; Hughes, 1952). In most studies of this description bacteria have been subcultured in fluid medium containing increasing concentrations of penicillin. In the present investigation solid medium was used to determine whether different types of variant could be isolated from the same culture.

SUMMARY: Phage lysis was induced in lysogenic cultures of Salmonella by means of nitrogen mustard, mustard gas, sulphathiazole, glutathione, and sodium thiol-acetate.

The liberation of phage particles by these cultures was inhibited by urethane, ascorbic acid, higher concentrations of thiolacetate than that necessary to induce lysis, and by incubating either at 41–43·5° or at pH 5·5. Incubation at 22° in some cases also had a slight inhibitory. action.

The following substances had no effect on the liberation of phage particles by these cultures: penicillin, streptomycin, chloramphenicol, Proflavine, Rivanol, colchicine, methionine, cobalt sulphate, sodium citrate, brilliant green, sodium tetra-thionate, sodium taurocholate, sodium biselenite, casein digest and yeast extracts. Cultivation either in atmospheres containing different amounts of oxygen, or at 28°, or in media containing varying concentrations of sodium chloride was also without effect.

Cultures did not become non-lysogenic as a result of prolonged passage in broth containing either sodium citrate, ascorbic acid or urethane.

SUMMARY: After inactivation by ultraviolet radiation, particles of two Rhizobium bacteriophages interfered temporarily with the multiplication of active particles of the homologous phage, in liquid cultures of their respective host bacteria. Inactivated particles did not affect the number of plaques produced by active particles in bacterial cultures on agar.

No evidence was found that particles that were inactive singly became active when two or more of them infected the same bacterial cell.

The rate of inactivation approximated closely to that of a first-order reaction. Exposing infected bacteria to visible light increased the residual activities of irradiated phage preparations by amounts equivalent to decreasing the doses of ultraviolet irradiation by a constant factor. Exposing either the irradiated phage preparations or the bacterial cultures separately to visible light had no effect.

Those ultraviolet irradiated phage particles which remained active were so altered that they became relatively unstable.

SUMMARY: Preparations of tobacco mosaic virus (TMV) inactivated by ultraviolet radiation interfered slightly with infection by active tomato bushy stunt (BSV) and Rothamsted tobacco necrosis (RTNV) viruses, and much more so with active TMV. Similarly, inactivated RTNV interfered slightly with infection by TMV and more so with active RTNV. In contrast, inactivated BSV did not affect the numbers of lesions produced by active virus preparations.

The residual infectivity of irradiated preparations of RTNV and BSV was greater when inoculated plants were exposed to light than when they were kept in the dark. This occurs because of some light-sensitive mechanism in the host cells, and exposing the irradiated virus preparations to visible light did not affect their infectivity. Irradiated preparations of TMV had the same residual infectivity whether plants were placed in the light or dark after inoculation.

Although the three viruses have particles of different sizes and shapes, the course of inactivation by ultraviolet with each approximated closely to that of a first-order reaction.

SUMMARY: The pigment of Plasmodium berghei, a recently discovered parasite of a wild rodent, Thamnomys surdaster, in the Belgian Congo, has been isolated from the infected red cells of young rats in which the strain is maintained in the laboratory. It has been shown by chemical and spectroscopical evidence to be haematin.

SUMMARY: A new species of heterofermentative Lactobacillus has been isolated from top-fermentation beer in which it oocurs as a contaminant. The organism is distinguished principally by the fact that it ferments only glucose, maltose and inulin and, in consequence, it has been designated L. malefermentans.

SUMMARY: Extracellular penicillinase produced by the growth of five different strains of the genus Bacillus in casein hydrolysate is rapidly inactivated at 100°, but can be strikingly protected against such inactivation by addition of 1% gelatin or high molecular weight substances present in tryptic digest and meat infusion broth.

SUMMARY: Streptomycin resistant strains of Bacterium coli were obtained by plating numerous 1 or 1·5 ml. volume cultures of a sensitive strain on plates containing 100 μg. streptomycin/ml. The growth rate of these strains was measured by mixing them with the sensitive strain and measuring the fall in the numbers of resistant organisms during several periods of daily subculture in streptomycin free broth. Their resistance to streptomycin and stability during successive subcultures in broth were also studied. They could be divided into three main types. All type I strains had identical slow growth rates, were completely resistant, though growing poorly at high streptomycin concentrations and were quickly replaced by rapidly growing slightly resistant variants when subcultured in broth. All type II strains had identical slightly more rapid growth rates, were partially resistant and gradually decreased their resistance in a stepwise manner during subculture. Type III strains had growth rates slightly less than that of the sensitive strain and of a degree of variability similar to those found in clones of the sensitive strain. They were completely resistant and were stable during subculture. They could be subdivided on the basis of one characteristic. Type III a strains grew as well in the presence or absence of streptomycin but type III b strains grew much more slowly in the presence of 1600 μg. ml. streptomycin or over. Since all the strains from any one plate were usually of the same type they were considered to have arisen from a single mutant cell. Since each mutation occurred several times in independent cultures and the number of tubes in which multiple mutations occurred was not greater than would be expected by chance, each type is considered to have arisen by an independent mutation.