- Volume 76, Issue 1, 1973

Summary: The prenols of Blakeslea trispora were found to be a mixture of C60-C60 prenols and α-dihydroprenols with C70 as the main type; the principal ubiquinones were ubiquinone-9 and its (side-chain) dihydro-derivative. A minus strain contained higher levels of prenols, ubiquinones, ergosterol, and β-carotene than a plus strain, and the levels of all four types of isoprenoid were higher again in mated cultures. The overall increase in isoprenoid synthesis in mated cultures was sometimes tenfold but the different isoprenoid types were not all equally affected by the mating process; possible roles for the different types in sexual differentiation are considered.

Summary: Treatment of growing Mycobacterium smegmatis with hydroxyurea decreased the DNA/protein ratio and markedly increased the specific activities of DNA polymerase and ATP-dependent deoxyribonuclease. These changes were similar to those produced by iron limitation of growth. Treating M. smegmatis with nalidixic acid also decreased the DNA/protein ratio but had no effect on the activity of either enzyme. Growth of M. smegmatis under conditions of zinc limitation did not diminish the specific activity of DNA polymerase thus not favouring a role for zinc in the action of this enzyme. The activity of the ATP-dependent deoxyribonuclease was, however, slightly increased. In previous reports the specific activity of DNA polymerase in this organism has been seriously underestimated due to interfering deoxyribonuclease and nucleoside triphosphatase. This was corrected by sufficient dilution of the extract. Revised specific activities of DNA polymerase in carbon-limited, nitrogen-limited and iron-limited cultures are, respectively, 10, 14, 11 and 64 units/mg protein.

Summary: Two variants of strain AC 17855 of Staphylococcus aureus, each carrying a well-defined penicillinase plasmid, were used in transduction to test the compatibility of two suggested plasmids in a wild strain DU4916 of Staphylococcus aureus. One of the plasmids in the wild strain, which was responsible for methicillin resistance and enterotoxin B production, was compatible with penicillinase plasmids of compatibility group I, whereas the other, responsible for penicillinase production, was not. Since the penicillinase activity in the wild strain was stimulated after addition of antipenicillinase of serotype A, it was concluded to be an α-plasmid.

Summary: Mutants of Escherichia coli K12 have been isolated which reduce nitrite 3 to 30% as rapidly as the wild-type. Activities of reduced nicotinamide adenine dinucleotide (NADH)-nitrite oxidoreductase were lower in cell-free extracts of these nirA* mutants than in the wild-type. The mutants grew on minimal agar, and their sulphite reductase activity was the same as in the wild-type.

Double mutants deficient in both nitrite and sulphite reductases were constructed, as well as recombinants which had regained one or both activities following recombination with Escherichia coli Hfr Hayes. The inability to reduce sulphite was due to an altered cysB† gene. Suspensions of nirA cysB + and nirA cysB bacteria reduced nitrite at similar rates, showing that sulphite reductase (which is a gratuitous nitrite reductase) contributes little to the rate of nitrite reduction in vivo. Cytochome c 552 was synthesized by nirA + cysB + double recombinants but not by nirA cysB or nirA cysB + bacteria. This data suggests that cytochrome c 552 is involved in nitrite reduction in E. coli either as a component of NADH-NO2 − oxidoreductase, or as an electron carrier whose synthesis is affected by the nir gene.

Summary: Conditions have been investigated which allow the mapping of the replication order of the genes on the pneumococcal chromosome by the density-shift method. Adequate synchrony of DNA replication was achieved by using cultures already involved in the strict regime designed to give competent cells; such cultures were grown for 30 min into the stationary phase and then diluted into the medium in which the density-shift will occur. The shift was achieved by changing from either (i) ‘light’ peptone medium to synthetic medium containing 5-BU, or (ii) peptone medium prepared in D2O to ‘light’ peptone medium. Samples of such cultures were lysed and centrifuged in caesium chloride and the gradients so formed fractionated and analysed for the transforming activity for the genetic markers. A map giving the order of replication of eleven markers is described.

Summary: Mutants showing oscillatory variation between H-type carrying phase-1 antigen and O-type were isolated from a diphasic derivative of Salmonella typhimurium. The rates of variation from the H-type to O-type were about 10−4/bacterial division and those in the reverse direction 10−3 to 10−4, which are very similar to the rates of variation from the phase-1 to phase-2 of the parent strain and vice versa. Transduction analyses showed that their mutation sites were in H2 (the phase-2 flagellar antigen gene). In O-type bacteria the expression of both the endogenote H1 (the phase-1 flagellar antigen gene) and the exogenote H1 introduced by abortive transduction were repressed. These results indicate that the bacteria are flagellate (H-type) in phase-1 and non-flagellate (O-type) in phase-2, i.e. they are H1-repressor-positive phase-2 non-flagellate mutants (H-O variants). The occurrence of H-O variants strongly supports the hypothesis that there is a special H1-repressor gene in the H2 operon which is concerned with the regulation of H1 expression in phase-2 bacteria.

Summary: New types of donor strains have been obtained by indirect selection froman IF strain bearing the autonomous plasmid SCP 1. The new donors differ from the previously known type of donor (NF) in being, usually, unstable, segregating numerous IF and UF variants, and in their pattern of donation to UF strains (recipient strains lacking SCP 1). Whereas the chromosome fragments donated by NF strains have neither end at a constant position, those transferred by the new donors have one constant and one variable end. The new donors are designated according to the marker donated with the highest frequency - that is, nearest to the constant end of the chromosome fragments. It is postulated that they arise by interaction between SCP 1 and the chromosome, perhaps to produce substituted plasmids analogous to F prime strains of Escherichia coli, which may mobilize the chromosome by donor crossing-over. Most of the new donors had a white colony phenotype, although producing apparently normal spores.

Summary: The isolation of a group of phages attacking the actinomycete Streptomyces coelicolor A3(2) is described. One of the phages, VP 11, has been characterized, with emphasis on the ways in which it might aid studies on the host organism. VP 11 is a virulent DNA phage with a wide host range. It has a latent period of 40 min at 30°C and an average burst size of about 40. The phage has been examined electron-micro-scopically and found to belong in group B of Bradley’s morphological classification. It has also been shown to be host-cell reactivated after u.v.-irradiation. Two temperature-sensitive mutations have been shown to undergo recombination. The phage requires Ca2+ for stability and is very sensitive to chelating agents. Some of the difficulties encountered in using a mycelial organism as a host in phage studies are described and discussed.

Summary: The penicillinase locus is weakly linked to the ilvA and ilvD loci in Bacillus licheniformis. Transformants for these markers include up to 5% of transfor-mants for the penicillinase locus. Penicillinase mutants have been mapped in the structural gene and at least two regulatory genes. One regulatory gene is 90% linked to the structural gene, a second regulatory gene is 50% linked to the first regulatory gene. Another possible regulatory gene is unlinked to the others. Mutations in the first regulatory gene show it has a negative control function; the other regulatory mutations result in defective inducibility though the role of the gene products is not known. A model for the regulation of penicillinase synthesis in this organism is discussed.

Summary: Single components of virginiamycin M and S inhibit the growth of sensitive strains of Bacillus subtilis. The mixture of M and S halts completely the multiplication of double-sensitive organisms and of S-sensitive M-resistant mutants, but only partly inhibits growth of M-sensitive S-resistant cells, and is without effect on double-resistant mutants. Single virginiamycin components have essentially a bacteriostatic activity, whereas the association of M and S is lethal for double-sensitive bacteria as well as for S-sensitive M-resistant mutants. This lethal effect is a two-step process, which occurs without appreciable lysis. No bactericidal effect can be observed when S-resistant cells are incubated with a mixture of M and S. The patterns of inhibition of protein synthesis in different mutants are similar to those of growth inhibition and viability loss: the latter effects are therefore consequences of the former. Virginiamycin S can have different effects on protein synthesis: it enhances the action of M in S-sensitive cells but prevents the inhibitory action of M in S-resistant mutants. It can be concluded that both virginiamycin components interfere with growth, protein formation and cell viability. However, only the gene for S-sensitivity is essential (i) for the lethal action of the association of virginiamycin M and S, (ii) for the inactivation of cells submitted to an alternate treatment with the two virginiamycin components and (iii) for rendering permanent the inhibition of protein synthesis.

Summary: Three antimicrobial nitroimidazole drugs (metronidazole, dimetridazole, and tinidazole) inhibit a range of Clostridia and the protozoan Trichomonas vaginalis; they have an identical site and mode of action as specific electron acceptors from the pyruvate phosphoroclastic reaction. Analogues of the drugs are compared and the structural requirements for activity explained. The nitrofuran (nitrofura-zone) probably has a different mechanism of action.

Summary: A difference in relative motility between virulent and avirulent Pseudomonas solanacearum was a possible factor in the shift from virulent to avirulent populations in still broth cultures. Virulent isolates grown on solid media or in tryptone yeast-extract glucose or glycerol broth for 24 to 48 h were mainly non-flagellated or non-motile, whereas avirulent isolates grown under the same conditions were usually flagellated and highly motile. Fimbriae were observed in electron photomicrographs of both types. A rapid preferential increase of avirulent bacteria occurred when mixtures were grown in still, but not in shaken, broth cultures; this relative increase was greatest close to the surface of the medium. Rapid aerotaxis of avirulent bacteria was demonstrated in mixtures of virulent and avirulent bacteria in a semisolid motility agar medium. Positive aerotaxis and high motility apparently favoured rapid increase of avirulent P. solanacearum when oxygen became limiting in broth media, in which virulent bacteria were not actively motile.

Summary: The ability of a variety of 2-substituted benzimidazoles to inhibit germ-tube elongation in Pithomyces chartarum conidia was determined. Contact with a solid surface, such as agar or glass-wool strands, was an essential requirement for germination. The degree of inhibition which benzimidazole derivatives exerted on germ-tube elongation varied markedly with the substituted group; 2-(4’-thiazolyl) benzimidazole (TBZ) was most active. Germ-tube elongation proceeded linearly on agar media and was unaffected by benzimidazole derivatives existing as cations. Inhibition occurred only when the pH of the medium neared, or exceeded, the pKa of the benzimidazole derivative being tested. Inhibition of respiration with exogenous glucose after 3 to 4 h of exposure of germinating spores to TBZ appeared to be only an indirect effect of TBZ action; TBZ, in concentrations 100 times that necessary to inhibit growth, failed to affect oxygen uptake or respiratory control of isolated mitochondria with a variety of substrates. TBZ inhibition of germ-tube elongation was partially eliminated by high concentrations of vitamin B12. TBZ treatment produced distorted mycelial growth with increased vacuo-lation and elevated RNA/DNA ratios. These data suggested a condition of unbalanced growth similar to that caused by vitamin B12 deficiency in bacterial and mammalian cells. TBZ may act as a precursor (replacing 5,6-dimethyl benzimidazole) in the formation of an inactive vitamin B12 coenzyme analogue.

Summary: Cladosporium resinae has been isolated from soil and air samples taken over a wide area in Africa, Australia and Europe (Parbery, 1969) and from fresh, estuarine and marine waters (Ahearn & Meyers, 1972). The organism’s biology and its potential for causing malfunctions in aircraft jet fuel systems were reviewed recently by Parbery (1971). A strain of C. resinae examined in our laboratory grows in deep culture on C10 to C14 n-alkanes (Cooney & Proby, 1971). Other strains grow on C9 to C18 alkanes (Tanaka, Shimizu & Fukui, 1968; Iizuka, Lin & Iida, 1970; Parbery, 1970). Since C. resinae is widely distributed in hydrocarbon-rich and in hydrocarbon-poor environments, and since it may have the potential to degrade hydrocarbons which are refractory to other biological agents, it was of interest to determine the range of hydrocarbons which C. resinae could use as sole source of energy and of organic carbon.