- Volume 22, Issue 3, 1960

Summary: Thymine-requiring Escherichia coli 15, t− and E. coli B, t− which contained 5-bromouracil in their deoxyribonucleic acid in place of thymine showed a marked increase in sensitivity to ultraviolet (u.v.) radiation. The effect was proportional to the extent of incorporation of 5-bromouracil under defined growth conditions and for a given medium. This increase in sensitivity to u.v. was not hereditary. A maximum u.v. dose-increase effect on survival of 3·5 was obtained; there was as high as a 20,000-fold decrease in the number of survivors as compared to irradiated bacteria grown in absence of the analogue. This effect was not obtained with bacteria grown before irradiation in 2-thiothymine (an inhibitor not incorporated into DNA), nor was there an increase in u.v. sensitivity in organisms grown under conditions of thymine starvation or of 5-flurouracil inhibition. Furthermore, bacteria which did not require thymine and did not incorporate 5-bromouracil did not show this sensitization effect. The increase in u.v. sensitivity caused by 5-bromouracil was annulled by thymine. 5-Iodouracil caused a lower increase in u.v.-sensitization. The extent of photo-reactivation was not as great in irradiated bacteria which had been grown in 5-bromouracil as in bacteria containing no analogue in their DNA. A u.v.-resistant mutant of E. coli 15, t− was isolated and found to be affected by 5-bromouracil in a manner similar to the slightly more u.v.-sensitive parent strain. Incorporation of 5-bromouracil did not result in a dose-increase effect on u.v.-induced mutagenesis at the thymine-dependent locus of E. coli 15, t−. Bacteria containing 5-bromouracil were similarly hypersensitive to heat but showed no increased sensitivity to H2O2 and several nitrogen mustards.

Summary: A number of obligately anaerobic rumen streptococci have been found capable of hydrolysing a mannan, galactomannan, contained in the endosperm of Cyamopsis tetragonaloba. Some of their morphological, cultural and physiological characteristics have been determined. The enzyme(s) associated with the breakdown of galactomannan is termed ‘galactomannanase’. It is possessed by some authentic rumen bacteria, and it is also found in significant amounts in raw rumen liquor. Galactomannanase in bacteria-free rumen fluid is postulated to be released into it by the prior growth of micro-organisms attacking the β-1:4 linkage such as cellulose, cellulose derivatives and galactomannan. A survey of a number of non-rumen bacteria revealed that they do not elaborate galactomannanase. Ability to hydrolyse galactomannan seems confined to a specialized group of anaerobic cocci of the rumen. Procedures for the purification of galactomannan and galactomannanase are described.

Summary: The absorption of molecular oxygen by chromous salts provides one of the most efficient methods of producing anaerobic conditions. In previous applications to anaerobic culture, hydrogen and chromous ions were produced by the action of sulphuric acid on chromium; chromium metal powder suitable for use in this method is however difficult to obtain. An alternative method of generating hydrogen and chromous sulphate from a mixture of chromic sulphate, zinc and sulphuric acid is described. A new indicator of anaerobic conditions which can be used repeatedly is also described.

Summary: Examination of mycelial extracts of the dermatophyte Microsporum canis indicated the presence of most of the enzymes of the Embden-Meyerhof and hexosemonophosphate pathways of carbohydrate metabolism, and those of the tricarboxylic acid cycle.

Summary: The effects of several dyes on the growth on solid culture media of several strains of Azotobacter chroococcum, A. vinelandii, A. agile and A. beijerinckii were studied. Some of the dyes inhibited the growth of one or more of the Azotobacter spp. tested. From our results, we conclude that A. chroococcum, A. vinelandii, A. agile and A. beijerinckii are different species, well characterized by their behaviour to the dyes. We propose a scheme, based on the action of 1/25,000 (w/v) Pyronine and 1/50,000 (w/v) Diamond fuchsin which differentiates the four Azotobacter species quickly and easily.

Summary: The ability of a culture of Neurospora crassa to produce a macroconi-dium or a microconidium is determined (irreversibly) at a particular period during development. The determinative periods for macroconidiation and microconidiation are not always coincident. In some strains, prevention of conidial formation for a period encompassing the earlier of the two determinative periods, followed by a removal of the restriction allowing conidiation to proceed, causes a complete switch in the conidial character, so that strains which are normally macroconidiate may be induced to produce only microconidia. The phenotypic changes are not due to permanent genetic changes in the cultures. This phenomenon was observed only when normal growth proceeded during the time when conidial differentiation was prevented.

Summary: Two temperature-sensitive genes are described which affect conidia- tion in Neurospora crassa. One (acont ) decreases the length of aerial hyphae at 35° but not at 25°. Those strains (col-1; msum ; acont and col-1; m+ ; acont ) which have short aerial hyphae at 25° are aconidiate at 35°.

Growth on a rich conidiating medium results in the non-expression of acon1 in some but not all of the acont strains tested. To explain the observations on conidia- tion in the acont strains it is suggested that acont is active during a certain period in the ontogeny of the culture, this period being independent of genotype and environment.

Another genotype col-1; m; acont+ has a phenotype which is dependent on the incubation temperature. At 25° it is microconidiate but at 35° it is macroconidiate. Since col-1; m + strains are aconidiate, the m gene determines whether any conidia shall be produced, but the type of conidia formed is determined by the ambient temperature. The sum gene removes this environmental control of conidial phenotype, the col-1; m sum strains being macroconidiate at both temperatures. The sum gene may be described therefore as a canalization gene.

Summary: Excised soybean root nodules exposed to an atmosphere containing an excess of 16N2 incorporated the label first into the centrifugal fraction containing the intracellular membrane envelopes and small amounts of bacteroid cell walls. The 15N concentration then increased in the soluble portion of the nodules. The bacteroid fraction was not labelled after 2 hr. exposure of the nodules to 15N2. In ageing nodules incorporation of 15N into the soluble fraction declined before incorporation into the membrane fraction. The inhibitory effects of CO, N2O and H2 on 15N2 incorporation in the various fractions were studied; the results suggested differential inhibition. The membrane fraction contained 8·5 % (w/v) total N, 37 % (w/w) lipid, had a negligible O2 uptake in the presence of substrates and had an absorption spectrum suggestive of the presence of porphyrin compounds. Further fractionation of the membrane fraction indicated that the 15N was associated with the lighter particles and was only partially soluble in 3n-HCl. The possibility that the membrane fraction contained the site of primary Na activation is discussed.

SUMMARY: The microbial populations of rhizosphere soil from pea varieties Onward, susceptible to wilt by Fusarium oxysporum f. pisi race 1, and Wilt-Resistant Alaska were assessed at six successive plant-growth stages, by the dilution plate technique. The most commonly found rhizosphere organisms were: Gliocladium roseum, Penicillium spp., bacteria, Fusarium roseum, F. oxysporum, F. solani, Mortierella spp., Rhizopus stolonifer and Trichoderma viride. Root exudate from variety Onward stimulated growth and sporulation of some of the more prevalent 24 of 60 different species among 137 morphologically different isolates of fungi and bacteria. Testing the rhizosphere isolates for their in vitro effects on the pathogenic Fusarium showed that 15 % had no effect, 29 % were slightly inhibitory, 42 % considerably more and 14 % strongly inhibitory. Prominent among the strongest inhibitors were a few bacteria, Gliocladium roseum and strains of F. oxysporum, the last showing that intraspecific inhibition occurs among the Fusaria.

When ten of the more prevalent rhizosphere fungi were grown in media containing rhizosphere soil extract, root exudate or both, their ability to inhibit the pathogenic Fusarium greatly increased; the most inhibition was obtained with culture filtrates of fungi grown in the presence of both rhizosphere soil extract and root exudate. Morphologically different isolates of Gliocladium roseum and Fusarium oxysporum inhibited the pathogenic Fusarium to different extents, showing that these species contain physiologic strains that could act differentially towards F. oxysporum f. pisi in the rhizosphere.

The rhizosphere of the wilt-resistant variety Alaska contained no more inhibitory isolates than the rhizosphere of the wilt-susceptible Onward. Although there were more micro-organisms per unit of dry rhizosphere soil of the susceptible variety, the species isolated from the rhizospheres of the susceptible and resistant varieties did not differ qualitatively.

Rhizosphere micro-organisms that were more prevalent up to the time that Fusarium invaded the host roots were not prominent among the group most antagonistic towards the Fusarium. In addition, there was no correlation between stimulation of rhizosphere organisms by root exudate and their antagonism towards the Fusarium. This implies that competition between pathogenic Fusarium and the other rhizosphere micro-flora for nutrients in root exudates may be at least as important as overcoming antibiosis in maintaining successful growth of the pathogen near host- root surfaces. Although these results were obtained in vitro, they suggest that rhizosphere soil extract and microbial metabolites together deter the growth of Fusarium oxysporum f. pisi near pea roots, and that the growth-promoting effects of root exudate from the wilt-susceptible pea variety Onward are partially offset by its ability to increase inhibition by some of the other rhizosphere inhabitants.

SUMMARY: The inhibitory titres of ovine and bovine submaxillary gland mucoproteins (OSM and BSM respectively), urinary mucoprotein, ovomucin and of the heat-stable seromucoid fraction of six animal species were determined under standard conditions against the same set of ten indicators derived from influenza viruses. By expressing relative rather than absolute titres ‘indicator profiles’ were obtained permitting direct comparison. OSM and BSM gave the most characteristic individual profiles and they closely resembled each other. Since the basic structures of the prosthetic groups of OSM and BSM are known to be identical, the close similarity of the profiles is regarded as resulting from this identity. A similar relationship seems to hold for the heat-stable mucoprotein fraction of various animal sera which have nearly identical profiles though distinctly different from the profile of the submaxillary mucoproteins.

SUMMARY: The growth curve of Corynebacterium diphtheriae in aerated submerged culture was studied. It showed a logarithmic phase followed by a period in which growth was linear when plotted on an arithmetic scale. There was then a phase of retardation of growth and finally a stationary phase. There was no lag phase. There was no simple correlation between the amount of growth and the amount of toxin produced, although in cultures as growth increased toxin also increased. No relationship was found between toxin production and the formation of catalase or the disappearance of maltose. The relationship between porphyrin and toxin production requires further investigation.

SUMMARY: The uptake of iron by Corynebacterium diphtheriae growing in complex medium was found to be rapid and quantitative, even when the iron concentration of the medium was high enough to abolish toxin production completely. The presence of this inhibitory concentration of iron (3 µg./ml.) did not alter the duration of logarithmic growth nor did it affect the shape of the growth curve in any other way. The ferrous and ferric forms of iron were taken up equally well by the organism and appeared, weight for weight, to give the same final toxin titres. Ferrous iron, however, appeared to begin to exert its effect on toxin synthesis much earlier in the growth period than did ferric iron. It is suggested that perhaps only ferrous iron is inhibitory and that ferric iron requires to be converted to the ferrous form before exerting its effect.

SUMMARY: Carbon dioxide stimulates the growth of Streptococcus bovis and the production of the extracellular enzyme dextransucrase. The growth of cultures in the presence of 14CO2 resulted in the incorporation of carbon-14 into aspartic acid, with lesser amounts in threonine, glutamic acid, adenine, guanine, uridylic acid and cytidylic acid. Organisms grown with labelled aspartic acid did not utilize it to any extent; the principal source of this amino acid was from CO2-fixation reactions. The stimulation of growth by CO2 is considered to be due to biosynthetic reactions involving CO2 which lead to a sufficient supply of the intermediates required in nucleic acid and protein synthesis.

SUMMARY: Streptococcus faecalis has been grown anaerobically in continuous culture on a defined medium. Under these conditions it is possible to maintain (a) the glucose concentration, (b) the tryptophan concentration, and (c) the generation time at predetermined values, and to study the effects of changes in these variables on the culture. When growth was limited by the glucose supply, the glucose yield constant (dry weight of cells formed/weight of glucose used) was greater than when tryptophan was limiting. The glucose yield constant under conditions of tryptophan limitation progressively fell with increasing supplies of glucose until it reached a minimum value. Under conditions of tryptophan limitation and large excess of glucose, the amount of glucose used per unit weight of cells per unit time remained roughly constant irrespective of growth rate. It is concluded that the needs of cell synthesis in S. faecalis do not control the rate of glucose breakdown, i.e. the rate of the energy-yielding metabolism. At slow growth rates the end products of glucose metabolism included volatile fatty acids, which were not present, or present in small amounts, at faster growth rates.

SUMMARY: Branches of the primary mycelium of a Streptomyces sp. were observed, by phase-contrast microscopy of living material, to form apparent anastomoses. No enlarged structures capable of interpretation as ‘initial cells’ were detected. It is suggested that certain of the large ‘spore-like bodies’ described by previous workers in studies upon Streptomyces spp. may represent protoplasts.

SUMMARY: Ultra-thin sectioning techniques showed that spores and crystals were formed together in vegetative B. cereus var. alesti, and that the crystals developed in close proximity to nuclear elements. The exosporium which surrounds the mature spore is not a remnant of the vegetative cell wall, which disintegrates, but arises as a discrete membrane within the cell and does not, at any stage, enclose the crystal. Carbon replicas confirmed what has hitherto been only speculation —namely, that the periodicity seen on the crystal is a true feature of the surface topography. Resolution in two dimensions was occasionally possible and its implications with regard to crystal structure are discussed.

SUMMARY: Species of Mallomonas known with the electron microscope are arranged in a new scheme of classification, extending that previously proposed. A number of new species are described and some known ones examined for the first time with the electron microscope. The development and internal structure of the scales of certain species is described. The proposed scheme of classification was developed as a result of the high resolving power of the electron microscope which enabled us to interpret features which can be faintly seen with the optical microscope. The scheme can, we believe, be used where the optical microscope alone is available. The feature which we have selected as the basis of classification differ from those selected by workers with the optical microscope only.

It was shown by MacLeod and his co-workers that among bacteria only the true marine forms have a specific sodium requirement. These all require this ion in concentrations of the order of a few tenths of 1 %. The non-marine bacteria studied by MacLeod were distinguished from marine forms by their lack of any requirement for sodium (MacLeod, Onofrey & Norris, 1954; MacLeod & Onofrey, 1956). In view of these facts, the following observation, which I made in the course of studying the amino acid nutrition of Rhodopseudomonas spheroides, seemed significant. This bacterium can grow very well in media of ordinary ionic strength and thus is not obviously marine. I observed that it did not grow in a medium in which an artificial mixture of amino acids had replaced an acid hydrolysate of casein. Since almost 40 % of the hydrolysate used was sodium chloride, I added a little NaCl to the medium containing the artificial mixture of amino acids. I then found that the growth was as rapid as in the medium made with casein hydrolysate. It was easily shown that a very much simpler mixture of amino acids permitted rapid growth in the presence of as little as 100 μg. NaCl/ml. This requirement for a low concentration of sodium seemed to set this organism apart both from marine and from terrestrial bacteria and thus to merit a more detailed analysis, the first results of which are reported here.

Summary: Washed suspensions of two strains of Escherichia coli which require vitamin B6 for growth form methionine in a reaction mixture containing homocysteine, serine, glucose, p-aminobenzoic acid and cobalamin only when pyridoxal or another member of the vitamin B6 group (except pyridoxamine phosphate) is also added.

Serine is replaced by glycine as donor of the required one-carbon unit, but the activity of glycine is markedly increased when the organism is harvested from a medium containing glycine. Pyridoxal is not required for the utilization of glycine by such organisms, but is essential when glycine has not been present during growth. It is concluded that growth on glycine induces the formation of an alternative, and more efficient, mechanism for using glycine as one-carbon donor which is independent of pyridoxal. This mechanism was studied in suspensions of an auxotroph requiring serine or glycine for growth by isotopic technique; C-2 of glycine is incorporated into the methyl group of methionine at four times the activity at which it appears in a serine pool. Free serine is therefore not an intermediate in the utilization of glycine as a one-carbon donor. Cobalamin is required for maximal activity of both glycine and serine in the reaction.