- Volume 59, Issue 3, 1969

SUMMARY: A small proportion of spontaneous penicillinase-negative mutants of the penicillinase-magno-constitutive Bacillus cereus strain 569/h prove to be highly unstable and revert to the relatively stable magno-constitutive parent phenotype at a high rate spontaneously. If incubated at 45° or at the normal growth temperature of 35° with chloramphenicol (20 μg./ml.) the organisms of a broth culture of this meta-stable negative strain can be induced to undergo 100% conversion to the fully de-repressed magno-constitutive state within 90 to 120 min. The conversion event appears to occur at random amongst the bacilli, whether single or joined in pairs; there is little or no phenotypic lag between committal to reproduction in the derepressed state and full expression of gene potential in the form of maximal rate of penicillinase production and a 1000-fold increase in penicillin resistance. Induced conversion is inhibited by nalidixic acid (10 μg./ml.).

It is concluded that the conversion event, for which some possible mechanisms are discussed, is controlled by a thermo-labile protein inhibitor.

SUMMARY: Growth of Mycoplasma laidlawii a in a tryptose medium, with lipid pre-extracted, containing charcoal-treated bovine plasma albumin, occurred only after addition of long-chain fatty acids. Of the long-chain fatty acids tested, positional as well as geometrical isomers of octadecenoic acids were effective in growth promotion; trans isomers were more effective in promoting growth and in lowering osmotic fragility than their corresponding cis isomers. Tetra-decenoic or hexadecenoic acids did not replace the growth requirement for an octadecenoic acid. Although fatty acids containing cyclopropane-rings promoted growth, a greater toxicity and lower growth response was observed. No fatty acid isomerization by this mycoplasma was detected and the octadecenoic acids added to the growth medium were recovered from membrane polar lipids unchanged. Fatty acid analyses revealed that myristic and palmitic acids were the major saturated fatty acid components of the membrane polar lipids. No differences were found in the fatty acid content or composition of membrane polar lipids from mycoplasmas grown at 25° and 37°. Major differences in the fatty acid composition between glycolipids and phospholipids were not apparent.

SUMMARY: Death of Escherichia coli after exposure to ultraviolet (u.v.) radiation or to γ-rays was markedly increased when the bacteria were incubated on media containing chloramphenicol or puromycin. A similar effect occurred when an irradiated histidine-requiring strain of E. coli b/r was deprived of its requirement but not when several other amino acid auxotrophic mutants of E. coli b/r were similarly deprived. The extra killing may be associated with the synthesis of RNA rather than be a direct consequence of inhibition of protein synthesis.

SUMMARY: Mutants of Bacillus anthracis which were prototrophic in a defined medium below 32° required either thymidine (mutant thy) or low concentration of thymine (mutant thytlr) for growth at 37°. No thymidylate synthetase was produced by these mutants at 37°. Normal enzyme activity was found in bacteria grown at 25°. Absence of thymidylate synthetase activity in bacteria grown at 37° could not be accounted for either by a heat-sensitive enzyme protein or by an inhibitor of this enzyme activity.

The incorporation of thymine by prototrophic bacteria of Bacillus anthracis was negligible at either temperature. Mutant thytlr and its prototrophic revertant both readily took up thymine at 37° but not at 25°. Thymine uptake by both prototrophic and thy bacteria was markedly enhanced by the presence of any of the deoxyribonucleosides except thymidine. Moreover, thymidine antagonized thymine uptake. No thymidine phosphorylase activity was detected in B. anthracis, but phosphorolytic decomposition of deoxyuridine was found and that of deoxyadenosine seemed likely. The phosphorolytic reaction of deoxyuridine resulted in an accumulation of deoxyribose by thytlr bacteria, whilst both wild-type and thy bacteria catabolized this sugar. The secondary mutation in thy bacteria presumably resulted in a defect in synthesis of 1,5-phosphodeoxyribo mutase or deoxyribose 5-phosphate aldolase (E.C. 4.1.2.4). Although no thymidine phosphorylase was detected in B. anthracis, resting suspensions of this bacterium transferred the deoxyribosyl moiety from thymidine to thymine. This indicates the presence of the enzyme nucleoside purine (pyrimidine) deoxyribosyl transferase in B. anthracis. This particular enzyme may also be involved in the increased thymine uptake in the presence of different deoxyribonucleosides.

SUMMARY: The endogenous respiration of vegetative amoebae, harvested during active growth, was similar in both the culture medium and in the high salt medium used to induce the encystation of starved amoebae. The respiration of starved amoebae and early stages of encystation was suppressed in high salt medium and stimulated when returned to the culture medium. A transient increase in respiration was observed early in encystation, while the respiration of later encystation stages decreased to the low level observed in mature cysts.

The respiratory metabolism of mitochondria isolated from encysting amoebae was similar to that of mitochondria from vegetative amoebae while cyst mitochondria exhibited little respiration. The catalase and acid phosphatase activities of amoebae increased during starvation and encystation.

SUMMARY: When the two heterothallic species Sordaria heterothallis and S. thermophila are crossed, two types of viable ascospores are recovered. The first, the mature black ascospore, is produced with a mature eight-spored ascus formed from an intraspecific fusion of nuclei of the same mating type. The second, the non-pigmented germinable ascospore, is produced by the interspecific fusion of nuclei of opposite mating types within an ascus in which all other ascospores are aborted. The non-pigmented ascospore is the product of the mixed genomes of the two species. It is a recombinant spore from which either species may be obtained by the partial substitution of its genome through successive backcrosses. Its inability to develop pigmentation, the irregular growth patterns of some of the strains which it produces and their inability to react in complementation tests, appear to be the result of a lack of affinity between the two species.

SUMMARY: A stable, ultraviolet-induced, albino mutant of Blastocladiella emersonii Cantino and Hyatt is described. It differs from wild type in: (a), capacity to form brown resistant sporangia (RS), both as 2nd and 3rd generation RS in clones derived from 1st generation ordinary colourless (OC) plants, and as 1st generation RS produced directly in response to exogenous bicarbonate; (b) the inhibition of growth by low concentrations of bicarbonate; (c) the longer generation time, stemming from a combination of decreased growth rate and delay in spore release until terminal sporangia have become unusually large; (d) the increased incapacity to discharge in situ on solid media with increasing temperatures above 23°; (e), reduced motility of zoospores and increased tendency to become amoeboid and encyst prematurely; (f), certain changes in the fine structure and organization of mitochondria and their associated lipid sacs, γ particles and the double membranes that surround nuclear caps and nuclei of spores chilled to low temperatures.

SUMMARY: Plasmodium berghei yoelii (p.b.y.) was found to cause an acute self-limiting infection in Balb/c mice, lasting for 14 to 18 days. A sharp fall in the primary response to sheep erythrocytes, as measured by the number of haemolytic plaque-forming cells in the spleen, and by the appearance of antibodies in the serum, coincided with high levels of parasitaemia between the 8th and 11th days of p.b.y. infection. A secondary response to sheep erythrocytes was similarly affected when animals were infected with p.b.y. 9 days before the second antigen injection. Mice were resistant to reinfection with p.b.y., which produced either transient or no parasitaemia, and no immunodepression.

In mice carrying an immunodepressive leukaemogenic virus by vertical transmission, infection with a similar dose of p.b.y. was usually fatal.

Murine sarcoma virus (Harvey: m.s.v./H) produces tumours and splenomegaly in newborn mice but very rarely in adults. When injected into adult Balb/c mice at the height of p.b.y. infection, m.s.v./H produced a high incidence of splenomegaly 4 weeks later, although the splenomegaly induced by the plasmodium alone had by then subsided.

These results are discussed in relation to Burkitt’s (1969) hypothesis of a causal connection between chronic malarial infection and development of Burkitt lymphoma in children.

SUMMARY: Yeast extract which promotes the growth of wild-type strains of Escherichia coli had a potent bactericidal action on thymine-less mutants. The active principle in the yeast extract was found to be adenosine. All of the other nucleosides and their bases tested except guanine, hypoxanthine and inosine also showed various degrees of bactericidal activity. The activity of adenosine was competitively annulled by the addition of excess thymidine to the medium, but thymine showed practically no anti-adenosine effect.

SUMMARY: Three Bdellovibrio bacteriovorus wild-type strains tested grew into long forms, up to 80 times their original lengths, when incubated in cell-free microbial extracts. This growth occurred both in extracts of organisms permissive and non-permissive for Bdellovibrio parasitic growth, but not in any other medium tested. Under certain osmotic conditions the long forms segmented into chains of cells. Some division of chains occurred. Only approximately 5% of the bdellovibrios grew into long forms. 3H-thymidine was incorporated into the long forms but not into short forms. A component of Pseudomonas aeruginosa extracts which supported growth of Bdellovibrios was macromolecular, heat stable and resistant to pronase, DNAse and RNAse.

SUMMARY: Strain-specific lipopolysaccharide extracted by hot phenol from two strains of Rhizobium trifolii was fully antigenic in rabbits with an injection schedule using Freund's adjuvant, and highly active in gel diffusion. A minor second diffusion line was considered to be due to a smaller fragment of the main molecule, since the antigen was converted almost entirely to this form by sodium dodecylsulphate and such disaggregated material absorbed antibodies to both forms of the antigen. Chemically the lipopolysaccharide showed some features related to those of the Enterobacteriaceae; for example, the presence of firmly bound lipid, 2-keto-3-deoxyoctonate, glucose, man-nose, fucose and, in one strain, a heptose. However, the lipopolysaccharide of R. trifolii was unusual in its very low phosphorus content and the presence of glucuronic acid. One strain diverged even further in its high content of carbohydrate, its lack of a heptose, its anionic behaviour and the gelatinous nature of some preparations; these properties might relate to the presence of a capsule-like structure which has been observed in old cultures of this strain.