- Volume 37, Issue 3, 1964

The synthesis of an inducible amidase by Pseudomonas aeruginosa 8602/a was studied in cultures growing exponentially in succinate medium. Induction by both the substrate inducer acetamide, and the non-substrate inducer N-acetylacetamide, was repressed by cyanoacetamide. Induction by 10−2mN-acetylacetamide was significantly repressed by 10−4m-cyanoacetamide, but repression of induction by 10−3m-acetamide required a tenfold excess of cyanoacetamide. Amidase synthesis in a medium in which acetamide was the sole carbon + nitrogen source was also repressed by cyanoacetamide, which under these conditions inhibited the growth of non-induced bacteria. Several tricarboxylic acid cycle intermediates, and related compounds, repressed amidase synthesis in exponentially growing organisms. Catabolite repression by propionate in succinate medium was decreased by increasing the concentration of acetamide. These findings are discussed in relation to general theories of regulation of microbial enzyme synthesis.

Species of the genera Mallomonas, Synura and Chrysosphaerella have been investigated in relatively few countries, and a study of their occurrence in Iceland provides additional information on their distribution. Several new species of Mallomonas (M. calceolus, sp.nov.; M. pugio, sp.nov.; M. clavus, sp.nov., M. maculata, sp.nov.) and one of Chrysosphaerella (C. multispina sp.nov.) were found together with numerous species already described. In this paper, observations with both light and electron microscopes are given in detail for the new species. Electron micrographs of the scales and bristles of known species are also shown and, where appropriate, compared with those of the new ones. Three out of the four new species of Mallomonas fitted into the existing taxonomic groups, one belonging to the Tripartitae, one to the Planae and one to the Torquatae. The fourth was added to a group already containing three isolated species. The new Chrysosphaerella species is of particular interest because only a few species have so far been described in this genus.

The survival of suspensions of lactobacilli and streptococci incubated at 37° in normal saline and in 0·1% (w/v) and 1·0% (w/v) solutions of dehydrated mucin was studied by counting the number of viable organisms present at regular intervals. The survival time was markedly prolonged in the mucin solutions. In the 1·0% (w/v) mucin solution most of the strains of lactobacilli and all the strains of streptococci were still viable at the end of one year. The mucin solutions appeared to be unchanged when compared with control solutions which had been inoculated with killed bacteria and incubated at 37°.

The base contents of deoxyribonucleate (DNA) preparations from 7 strains of Neisseria catarrhalis were determined chromatographically. Three non-overlapping classes were distinguished by mole % guanine + cytosine. These centred about the values 41% (2 strains), 42.3% (4 strains, including atcc 8193), and 44·5% (strain nctc 4403), Each of the 7 strains was capable of undergoing genetic transformation. DNA preparations from spontaneous streptomycin-resistant mutants of all 7 strains elicited transformation of recipient strains in all 49 possible combinations. Results with this group, therefore, do not support the hypothesis that success in transferring genetic information between 2 strains requires identity of average DNA base contents.

Differences of reciprocal transformation frequencies and of 4 physiological characteristies (nitrate reduction, pigment production on vancomycin-containing agar, hydrolysis of gelatin, and growth at 28°) appeared to separate 6 of the strains of Neisseria catarrhalis from the seventh (nctc 4103), which may properly be named N, cincrea.

Fourteen strains of Moraxella and possibly allied organisms were studied: M. liquefaciens, M. bovis, M. nonliquefaciens, oxidase-positive and oxidasenegative strains of Mima polymorpha and Herellea vaginicola. Classical bacteriological characteristics, capacity to undergo genetic transformation (resistance to 500 μg. dihydrostreptomycin/ml.), and DNA base composition were examined. Moraxella nonliquefaciens and Mima polymorpha var. oxidans were transformable (2 strains at frequencies of 1-4%). Attempts to elicit transformation of the remaining organisms were unsuccessful. The ability of DNA preparations from M. polymorpha var. oxidans to elicit high frequencies of transformation of Moraxella nonliquefaciens, and vice versa, indicated their close relationship. Moreover, their DNA base contents were indistinguishable (about 44·4% guanine + cytosine, 6 strains). The G + C contents averaged 43·1% for 3 oxidase-negative Mima polymorpha strains and 39·8% for 2 Herellea vaginicola strains.

Deoxyribonucleate (DNA) preparations from Moraxella nonliquefaciens elicited genetic transformation of Neisseria catarrhalis recipient cells, and vice versa. The frequency was low (0·0005% transformation for the most reactive of six strains), as might be expected of an interaction between two organisms as dissimilar as a rod and a coccus. Evidence that the hereditary change (attainment by susceptible cells of resistance to 500 μg. dihydrostreptomycin/ml.) was due to transformation was provided by the typical time course of the reaction, the typical linear response to decreasing concentrations of DNA below 0·1 μg./ml., and by tests of transforming activity of DNA preparations extracted from 11 dihydrostreptomycin-resistant (str-r) strains which arose by intergeneric transformation. These DNAs had relatively high transforming activity for recipient strains of both species. Thus, the str-r region of the transforming DNA molecule from a transformant strain of M. nonliquefaciens was recognized and genetically integrated by populations of N. catarrhalis recipient cells at frequencies as much as 10,000 times higher than those of DNA from strains of M. nonliquefaciens str-r (derived by spontaneous mutation). The results with DNA preparations from particular transformants are interpreted as indicating that the length of a DNA nucleotide sequence which is integrated by a cell during str-r transformation may differ for different cells of the same treated population.

A disaccharide was isolated by partial hydrolysis from the group specific polysaccharide of a streptococcus strain carrying the group antigen F. The most probable structure of the substance is 3-0-β-d-gluco-pyranosyl-N-acetyl-d-galactosamine. The disaccharide was 300 times more active than cellobiose in the inhibition of the F/anti-F system. This denotes that it is a component of the determinant group of the group antigen. Two other serologically active oligosaccharides were isolated from the hydrolysate. Though their structure was not fully elucidated, evidence was obtained that a tetrasaccharide consisting of two molecules of the disaccharide is an important part of a determinant group of the F antigen.

The growth of rabbitpox virus has been studied in monolayer cultures of HeLa (ERK) cells. At 36°, virus was adsorbed to cells at about one-tenth of the theoretical collision rate. The adsorbed virus penetrated the cells exponentially, the time for half penetration being about 1 hr. New infective virus began to appear at 5 hr, and the final yield at 24 hr was about 100 pfu per cell. The synthesis of viral antigen began 1 1/2 hr after infection of the cultures; this was 1 hr before the earliest appearance of viral DNA. When virus growth was complete, over 20 separate antigens could sometimes be detected in extracts of infected cells. The yield of antigens was not reduced when virus multiplication was completely inhibited by bromodeoxyuridine. It was concluded that the synthesis of viral antigens was directed by the DNA of the infecting virus, and not by the DNA formed during virus growth.

The addition of K and Na salts to cultures of Dermatophilus dermatonomus potentiated the effect of carbon dioxide (CO2) in stimulating hyphal growth and delaying sporulation; the salts had virtually no effect in the absence of CO2. The maximum production of these effects required the same minimum concentration, about 50 m-equiv. cation/l., of a comparably wide range of salts, as did maximum alteration of the chemotactic response of the zoospores to CO2. It is suggested that there may be a common mechanism by which salts sensitize both the zoospores and the growing stages to CO2. If these reactions are induced by the salts and CO2 in the skin of infected sheep, they would partly account for the observed rapidity of both hyphal penetration and the emergence of zoospores.

When the proportion of prototrophic revertants in a continuous culture of the tryptophan-requiring strain wp2 of Escherichia coli was adjusted to exceed about 10-7, a large increase (‘take-over’) often occurred after a variable delay, the proportion becoming as high as 50% in some cases. The phenomenon appeared to be correlated with a selective advantage of revertants which became attached, with parent auxotrophs, to the wall of the culture tube. After some hours the film of growth on the wall was composed of approximately 107 bacteria. It was quite different from the massive ‘sticky’ growth sometimes encountered in continuous cultures of E. coli. The experimental observations of this ‘take-over’ are quantitatively consistent with a hypothesis of wall adsorption of rather rare and readily attached variant prototrophs.

A sulphate-reducing bacterium (strain Norway 4) previously assigned to the species Desulfovibrio desulfuricans has now been found to contain cytochrome c 3 but not desulfoviridin. The organism resembles strains of D. desulfuricans which contain both pigments, in its morphology, nutrition, metabolism and hydrogenase activity. It is considered to be a mutant which has lost desulfoviridin. This work has not revealed the function of desulfoviridin.

The identity of the polysaccharide antigens of Streptococcus mg and streptococci with group antigen F and type antigen III is shown by precipitation reactions with formamide extracts, cross-absorption tests, sugar composition and by the inhibition of the quantitative precipitation reaction. On this basis Streptococcus mg can be classified as an f III strain.

The relationship between Streptococcus mg and Streptococcus salivarius type I is explained by their common reactions with anti-III serum. Inhibition of the quantitative precipitations with simple sugars suggest that the determinant groups of the type III and the ‘salivarius’ antigen are not quite identical, although both antigens contain a β-glucosidic and a galactosidic group.

A second unrelated antigen has been found in some ‘salivarius’ strains alone (represented by strain 51) or together with type III antigen. The quantitative precipitation of the strain 51/anti-strain 51 system was only slightly inhibited by rhamnose.

The qualitative composition of the sugar components of the formamide extracts of Streptococcus mg, f III, both ‘salivarius’ types of 0 III are compared.

The polysaccharide components of an encapsulated and a non-encapsulated strain of Lactobacillus casei var. rhamnosus were compared. The main capsular component was a polysaccharide consisting of rhamnose, glucose and galactose. This polysaccharide resembles, chemically and serologicaly, one of the two polysaccharide components normally found in the cell wall of L. casei var. rhamnosus. Since the cell wall of the encapsulated strain lacks the rhamnose-containing polysaccharide it seems likely that the capsule represents polysaccharide which has failed to become attached to the cell wall mucopeptide.