- Volume 100, Issue 2, 1977

The sensitivity of Saccharomyces cerevisiae α-Σ1278b to methylammonium was dependent on the nature of the nitrogen source. Yeast strains carrying novel mutations, allNmr or argNmr, were isolated by selection for methylammonium resistance in media with allantoin or arginine as the sole nitrogen source. The mutations result in a considerable relief from nitrogen metabolite repression of allantoinase synthesis (allNmr), or of arginase and ornithine transaminase synthesis (argNmr and, to a lesser extent, allNmr). Both mutations were recessive to the wild type and were neither linked to each other, nor to the structural genes of allantoinase, arginase and ornithine transaminase. Hence they represent regulatory genes without operator characteristics. Experiments with ammoniumlimited continuous cultures indicated that ammonium transport was not affected by the allNmr and argNmr mutations. Ammonium repression of catabolic NAD-dependent glutamate dehydrogenase was also unaffected. The argNmr locus, in cooperation with other loci, appears to control nitrogen metabolite repression of the arginine degradative pathway; it is probably pathway-specific. The allNmr locus may have a general function in nitrogen metabolite repression of various degradative pathways since the allNmr mutation causes resistance to methylammonium in the presence of several metabolically unrelated nitrogen sources.

The antimicrobial drug 1-methyl-2-nitro-5-vinylimidazole (MEV) preferentially blocked DNA synthesis, was mutagenic and induced coliphage λ in Escherichia coli. The antibacterial effects of MEV are the consequences of repairable damage to DNA, as shown by hypersensitivity of recA and uvr strains to MEV and related drugs, stimulation by MEV of DNA turnover which was dependent on the product of the uvrA gene, and the presence of cross-links in DNA from MEV-treated bacteria.

Although the target of the antimicrobial drug 1-methyl-2-nitro-5-vinylimida-zole (MEV) has been shown to be DNA ( Goldstein et al., 1977 ) the drug was ineffective in cell-free systems because it was not activated. Both the rate of metabolic activation of MEV and its antibacterial activity were increased when bacteria were grown in limiting oxygen. Mutants of Escherichia coli which were conditionally resistant to nitroimidazoles and nitrofurans were defective in drug activation. The activities of these drugs against E. coli correlated with their rates of metabolism. The antimicrobial spectrum of the drugs appeared to be related to their reducibility by different species.

Attempts were made to obtain recombinants between the morganocinogenic factor Mor174 and R plasmid R772 by transductional techniques. Transduction frequencies of the kanamycin resistance marker of R772 to Proteus mirabilis pm5006 or Providence p29 carrying Mor174 by phages 5006M and PL25, respectively, were 1000-fold higher than to the corresponding Mor174− strains. The frequency of phage P1-mediated transduction of the same marker to Escherichia coli J62 was high and was not affected by the presence of Mor174 in the recipient. Transduction of the kanamycin resistance marker to pm5006 yielded heterogenote-like transductants. Transduction of the same marker to pm5006 with Mor174 as resident resulted in transductants which not only yielded low frequency kanamycin resistance transducing particles on induction but could transfer Mor174 and the transduced marker independently by conjugation. It was suggested that Mor174 exerted some function in establishing a transductionally shortened R factor. Mor174 also possibly played a role in the separation of the phage component of the transducing particle from the R factor portion. The severed phage genes could then integrate in tandem to a cryptic prophage to render transductants inducible. A phage 5006M lysate of pm5006(Mor174R772) produced a cotransductant. This transductant could not, possibly due to more extensive transductional shortening, transfer markers by conjugation. Induction yielded some particles which could cotransduce the markers to pm5006(P-loc). With assistance of the latter conjugative plasmid, markers of Mor174 and R772 were transferred as a unit by conjugation to strain J62. Phage PI reared on the latter transconjugant cotransduced the genes for Mor174 activity and kanamycin resistance. Morganocin production by the recombinant equalled that of Mor174.

An element controlling chloramphenicol resistance (chl) was detected in Streptomyces coelicolor a3(2). Strains sensitive to 1 μg chloramphenicol ml−1 were obtained among dark scarlet variants. Transfer of the resistance factor was attempted in matings between chloramphenicol-resistant (Chl+) and chloramphenicol-sensitive (Chl−) strains, both of which lacked the SCPI fertility factor. Transfer of chl was obtained at a much higher rate than that expected for chromosomal markers in SCP1− × SCP1− matings. However, in these particular crosses the latter was also several times higher than usual. All recombinants for chromosomal markers were Chl+. Attempts to locate the chl element failed to distinguish between a chromosomal and an extrachromosomal site. The observed increase in the recombination frequency for chromosomal markers suggests that the chl element may promote recombination.

Most of the his + hybrids from crosses between the Escherichia coli donor Hfr45(O8:K27) and different E. coli O9 recipients expressed the donor O8 antigen specificity and produced the capsular antigen K27. Therefore these hybrids must have inherited the his-linked donor rfb region determining the synthesis of O8 specific polysaccharides as well as his-linked genes involved in K27 antigen synthesis. In the living state these hybrids were inagglutinable in O8 antiserum like the donor cells. However, when E. coli K12 and O8:K42− were used as recipients most of the his + hybrids were agglutinable in O8 and K27 antisera. The amounts of K27 antigen present in these hybrids, designated as K27i (intermediate) forms, were sufficient to evoke the production of K27 antibodies in rabbits, but insufficient to inhibit O-agglutination of the respective cells. The additional transfer of the trp region of E. coli O8:K27 into such K27i forms frequently resulted in O-inagglutinable K27+ hybrids. This is attributed to the introduction of trp-linked genes which apparently play a role in the synthesis of K27 capsular antigen. Thus it is concluded that at least two gene loci, one close to his and the other close to trp, are required for the synthesis of the complete capsular antigen K27.

Precipitating antigens from Theileria parva have been partially purified. Two antigens from each of the schizont and piroplasm stages of the parasite were identified; the major antigens from the two stages shared the same specificity. The antigens showed considerable molecular heterogeneity, almost certainly a result of the preparative method, and they always contained large amounts of DNA. The piroplasm antigens were of parasite nuclear origin and the schizont antigens were probably of the same origin. The antigens were weakly antigenic, and the activity against them of humoral antibody from cattle immune to East Coast fever was low. These antigens do not appear to induce protection against East Coast fever.

Listeria monocytogenes, in doses of 2.·0 × 103 to 3·0 × 103 viable organisms, was injected into athymic nude mice, irradiated mice and mice treated with reticuloendothelial system-blocking agents. Viable counts on liver and spleen homogenates were made at intervals after infection. In both nude mice (nu/nu) and normal littermates (nu/+) of BALB/c background, the bacteria grew rapidly for 24 h but increased only slowly thereafter, to reach a plateau of about 105 per organ at 72 h. In nu/+ mice, the number of viable bacteria began to decrease after 6 to 9 days, with complete elimination by day 12. In nude mice, the number of Listeria remained at a stable level of approximately 105 per organ during the observation period of 21 days. In lethally irradiated nu/+ mice, bacteria grew progressively and extensively to reach 107 per spleen and 109 per liver by 72 h. Bacterial growth during the first 72 h was markedly enhanced by treatment with carbon particles, dextran sulphate 500 or silica. These enhancing effects were also observed in nude mice and in AKR, C3H/He and C57BL/6 animals. We conclude that both non-immune phagocytes and T cell-dependent mechanisms contribute to the resistance of mice to Listeria infection.

The optimum conditions for cellulase production in culture filtrates by Trichosporon cutaneum and T. pullulans were determined. With ball-milled filter paper as a test substrate maximum activity was detected 4 to 7 days after transfer from glucose to cellulose (ball-milled filter paper) as growth substrate. Comparison of the yeast filtrates with those from the moulds Trichoderma viride and Myrothecium verrucaria showed that the total activity of one strain of T. pullulans was comparable to that of the moulds with ball-milled filter paper as assay substrate. Activities were always lower when α-cellulose or dewaxed cotton were used as assay substrates. The main products of cellulose degradation were cellobiose and glucose, although the ratio of these products clearly differentiated between culture filtrates of the species examined. Xylanase activity was present in all the culture filtrates examined. Polyacrylamide gel electrophoresis of active filtrates produced strain-specific patterns of three to five stained bands with similar mobilities but an inactive filtrate lacked one band common to all the other filtrates.

Cell extracts prepared by ultrasonic disruption of 17 strains of the ‘rhodochrous’ complex and related taxa were compared by polyacrylamide gel electrophoresis and, for immunologic relatedness, by skin test reactions. Two organisms, Jensenia canicruria and Nocardia calcarea, gave similar gel patterns and skin test reactions, and are considered to be identical. Extracts of Nocardia rubra showed a strong antigenic relationship with those of three Nocardia pellegrino organisms (n325, n324 and n420) previously assigned to the ‘rhodochrous’ complex. Two Gordona organisms appeared to be less antigenically related to the ‘rhodochrous’ complex. Extracts of three of four organisms designated Lspi (Rhodococcus coprophilus Rowbotham & Cross 1976 ) elicited skin test reactions similar to those of the ‘rhodochrous’ strains. One Lspi strain, n650, showed striking similarities to the ‘rhodochrous’ complex strain n420 (Nocardia pellegrino).