- Volume 51, Issue 1, 1968

SUMMARY: Excystment agents (extract of Escherichia coli, living E. coli and glutamic acid) failed to cause excystment of Schizopyrenus russelli cysts in the presence of either emetine or compounds I and II (structurally based on emetine). A very high percentage of the cysts excysted in the presence of the excystment agents after the removal of emetine, showing that the treated cysts were viable. Ninhydrin reaction, using a fixed amount of glutamic acid and increasing concentrations of emetine, showed progressive inhibition of colour development. This suggests the possible binding of excystment factor to emetine, thus preventing excystment. Excystment inducing property of the excystment agents could not be prevented in the presence of carbarsone. When the cysts were treated with sodium lauryl sulphate and then with emetine or with sodium lauryl sulphate and emetine together, there was hardly any excystment. Sodium lauryl sulphate rendered the cyst wall permeable to emetine and the latter killed the cysts.

SUMMARY: The structure of surface layers of the bacterial form and different types of the L-form of Proteus mirabilis was studied by electron microscopy of thin-sectioned organisms. Morphological data confirm the distinction between the cell wall-less protoplast-L-form and the wall-containing spheroplast-L-form. Organisms of the protoplast-L-form have only one surface-integument, presumably the cytoplasmic membrane. These forms never revert to the bacterial form. The spheroplast-L-form comprises reversible forms (unstable-sphero-plast-L-form) as well as non-reverting strains (stable spheroplast-L-form). In both spheroplast-L-forms two surface integuments are always present: a cytoplasmic membrane and a superposed cell wall. In sections of isolated cell walls of normal Proteus bacteria and in wall material spontaneously dissociating from damaged cell walls of spheroplast-L-forms the triple-layered ‘unit membrane’ is a prominent feature. Thin sections of isolated cell wall lipopolysaccharide identify the unit membrane as a specific structure of this polymer. The thickness of the murein (syn. mucopeptide, mucopolymer) in isolated murein layers (‘murein sacculi’, Weidel & Pelzer, 1964) from cell walls of normal Proteus bacteria was found to be approximately 20–25 å.

SUMMARY: The presence of numerous bacteria and diatoms attached to the sand grains of a littoral beach have been shown by fluorescence microscopy. Bacteria and diatoms were found in a viable condition to depths exceeding 10 cm. The rate of uptake of [14C]-acetate was measured over the range 10–5000 μg./l. and the results analysed by Michaelis-Menten kinetics. By the use of autoradiography it was shown that the bacteria alone were responsible for the uptake of [3H]-acetate. It is concluded that algal heterotrophy is negligible in sea waters.

Several antibacterial agents were tested against a range of cytophagas and other bacteria representing types commonly found in soil and marshy places. From these tests two antibiotics (penicillin 15 units/ml. and chloramphenicol 5.0 μg./ml.) and two bile salts (sodium taurocholate 8.0 mg./ml. and sodium cholate 6.0 mg./ml.) were selected for incorporation into alkaline enrichment media to achieve selective growth of cytophagas. This mixture of antibiotics and bile salts was tested with a number of soils and its efficiency compared with several other methods for selective development of cytophagas; bile salts inhibited two common species. The most suitable mixture for the selection of cytophagas was enrichment medium with penicillin and chloramphenicol.

SUMMARY: Cultures of several diploid strains of Saccharomyces cerevisiae were found to contain about 0.5% of glycogen-deficient cells. Ultraviolet irradiation increased the mutant frequency to about 5%, while 40% of the population survived. The mutants were detected by plating cultures on nutrient agar containing 1% glucose and staining 3-day colonies with iodine; normal colonies became brown due to the stored glycogen whereas the mutants remained white. The size of the mutant colonies was normal. Most of the mutants have remained stable during subculture. Fractionation of the cellular carbohydrate confirmed that the mutants were deficient in glycogen. Glucose concentration in the growth medium had a marked influence on glycogen storage. When the mutants were grown on nutrient agar containing 8% glucose, glycogen was stored and the mutants could not be distinguished by iodine-staining from the wild type. Glycogen-deficient mutants contained higher than usual proportions of respiration-deficient cells. Respiration-deficient colonies, whether derived from glycogen-deficient or from normal cultures contained appreciably less glycogen than those of the wild-type yeast.

SUMMARY: The synthesis of glutamine synthetase in Escherichia coli under different conditions was studied. The optimal concentration of ammonium sulphate in the growth medium for the enzyme synthesis was 0.4 mM. When glucose was limiting growth the enzyme synthesis became dependent on oxygen. L-Glutamine repressed synthesis of the enzyme and, to a lesser extent, that of glutamate dehydrogenase. L-Arginine, L-asparagine, D-glutamine, L-methionine and L-tryptophan also decreased synthesis of glutamine synthetase. On the other hand, L-glutamate induced the enzyme synthesis; L-isoleucine, L-leucine and L-valine also increased it. Acetyl-L-glutamine did not affect the enzyme synthesis. D-Glutamine was much less active than L-glutamine as a substrate in the γ-glutamyl transfer reaction. At low concentrations, both aza-L-serine and 6-diazo-5-oxo-L-norleucine increased the specific activity of glutamine synthetase in the bacteria.

SUMMARY: Phytophthora palmivora is more exacting in its nutrition for extracellular enzyme production than for growth. All of thirteen defined media tested supported fairly good growth. The major enzymes detected were: endopolygalacturonase (endo-PG), maceration factor (MF), α-L-arabinofuranosidase (AF) and phenolase. These enzymes were not detected in four of the five natural media tested. In egg-plant extract, traces of endo-PG, MF and pectin-methyl esterase were detected and higher activities of AF and phenolase produced. Inability to detect the enzymes in cultures in other plant extracts was possibly due to their inactivation by the oxidized phenols formed. The inability to detect other enzymes in cultures in defined media, especially those enzymes already implicated in plant diseases, may also be due to the fact that the media tested in the present work were not suitable for their induction. The most suitable basal medium for growth as well as good production of the major enzymes consisted of (%): 1, pectin; 2.5, glucose; 1, asparagine; 0.025, MgSO4. 7H2O; 0.5, Difco yeast-extract; traces of thiamine.

SUMMARY: Strains of Phytophthora cactorum resistant to streptomycin were obtained by incubating zoospores in liquid medium containing the drug. One of the strains required streptomycin for growth. In this dependent strain and one of the resistant strains, the dependence or resistance was transmitted to both asexual and selfed sexual progeny without any segregation for sensitivity. Change from dependence to resistance occurred with low frequency. Some of the resistant and the dependent strains showed much greater morphological variation than the wild type. Continuing segregation for morphological characters was observed during vegetative growth and in the asexual progeny of single zoospores, and the ability to segregate was not lost following sexual reproduction (selfing). Cultures were more variable after storage at 3°. There was evidence suggesting a particulate nature for the determinants of these morphological differences, normal zoospores having one such determinant.

SUMMARY: Changes in competence of Bacillus subtilis 168 try − in relation to generation time and under other conditions were examined. When the generation time increased or decreased from that associated with maximum competence, competence decreased. In a culture in balanced growth, competence remained at the same level for long periods. In supplemented medium, more bacteria became competent than in minimal medium.

Aeration stimulated the development of competence which reached a higher peak than in an unaerated culture. When the medium was inoculated with spores, competence also developed. The smaller the inoculum of spores, the later the appearance of competence.

Waves of competence were often seen along the main curve of competence, and were influenced by the compositions of the media and by the inoculum size.

During the growth cycle in a closed culture the bacterial cells became competent and then lost this property. Competence was thus a transient state.

The optical density of the bacterial suspension was a good guide to the development of competence, but varied with the strains used and with the cultural conditions.

SUMMARY: The process whereby bacterial cultures are alternately grown and then irradiated (γ-radiation) through several ‘cycles’ has been studied as a means of developing radioresistant cultures of Escherichia coli 1. The nature of the environment at the time of irradiation influenced the extent of development of radioresistance. Radioresistance development was higher when the bacteria were irradiated in an organic environment than in an inorganic environment. It is not thought that radioresistant mutants would be produced in high numbers by this type of process during a dose-fractionation procedure of food irradiation.

SUMMARY: Salmonella typhimurium tolerated the replacement of about 70% of the thymine in the DNA by 5-bromouracil (BU). In phage PLT-22 transduction, the presence of BU in the donor DNA had no effect on the linkage relationship of two contransduced markers and did not conclusively alter the ratio of complete transductants to abortive transductants. The yield of transductants per plaque-forming unit was more than doubled by the treatment of the donor bacteria and phage with BU. However, more than half of the BU-treated phage particles, detected by electron microscopy, did not form plaques; when the multiplicity of infection was calculated from the titre of physical particles, the frequency of transductants was normal. It is concluded that recombination was not affected by the substantial incorporation of BU into the donor DNA. Treatment of the recipient bacteria with BU slightly modified recombination by decreasing the frequency of transductants by about 40% and the linkage of the cotransduced markers by about 5%. Because comparable results were not obtained when the donor DNA contained BU, it is suggested that these effects resulted indirectly from the treatment of the recipient bacteria.

SUMMARY: Killer strains of yeast, Saccharomyces cerevisiae, liberate a killer factor into the medium which kills senstive yeast strains. The growth conditions necessary for the production of stable high-titre killer solutions and a biological assay for the killer factor are described. Purification was achieved by fractional precipitation with (NH4)2SO4, dialysis, gel filtration and ultrafiltration. The fractionated killer factor is an unstable macromolecular protein which is inactivated by papain. The death of sensitive cells is not coincident with absorption of the killer factor, but can be delayed or prevented by variations in the environmental conditions. Sensitive cells are most susceptible to the action of the killer factor when in log phase. Treated resting cells on entering log phase are killed immediately.

SUMMARY: The formation of chlorophyll in non-proliferating etiolated cells of Euglena gracilis var. bacillaris is inhibited by some antimetabolite analogues of vitamins. The cell size and cell mass of light-grown euglenas is considerably increased in vitamin B 12 deficiency. The inhibitory effect of 2,6-diaminopurine on chlorophyll formation in non-proliferating euglenas was not annulled by vitamin B 12; 6-mercaptopurine, sulphanilamide and benzimidazole were without effect. Isoniazide inhibition is not reversed by niacin: surprisingly, the vitamin itself is markedly inhibitory. The inhibitory effect of niacin, however, is prevented by pyridine-3-sulphonate. Niacin and its analogues were more inhibitory to growth in the dark than in the light. The inhibition of growth by niacin in the light is annulled appreciably by either glucose or pyruvate, or an overwhelming concentration of vitamin B 12. Aminopterin, desoxypyridoxine and 2-chloro-p-aminobenzoic acid do not have any effect on chlorophyll synthesis in non-proliferating euglenas; the last mentioned inhibits the growth of the alga more in the dark than in the light. Thiamine deficiency inhibits growth; such sub-optimally grown euglenas also synthesize less chlorophyll per cell on subsequent illumination under non-proliferation conditions.

The negative growth response of light-grown Euglena gracilis var. bacillaris to niacin suggests a microbiological method of estimating this vitamin in biological materials and pharmaceutical preparations up to concentrations of 70 μg./ml. in the growth medium. The 50% inhibition level of niacin in the light is 46 μg./ml.

SUMMARY: Cholesterol promoted oospore formation in Phytophthora cactorum; very few oospores were formed when cholestanol was incorporated in the medium instead. Above a critical concentration of cholesterol, cholestanol competitively inhibited oospore formation by cholesterol when both were added to the medium together. At low cholesterol concentrations, the addition of some cholestanol increased the number of oospores; further addition of cholestanol was inhibitory. Cholesterol and cholestanol stimulated vegetative growth to a similar extent.

SUMMARY: Purified cell walls were isolated from hyphae of Penicillium digitatum Sacc. and P. italicum Whem. Electron micrographs showed microfibrils in the walls. The walls are composed chiefly of carbohydrate material, mainly D-glucose, together with D-galactose, glucosamine and mannose. Only small amounts of protein were found. Fractionation with alkali and acid indicated that the walls contain several glycans.

SUMMARY: An immunological method based on the specificity of delayed-type skin reactions on guinea-pigs has been used for comparing 17 Nocardia strains. By this method, 4 isolates labelled Nocardia farcinica, four labelled N. asteroides and 1 strain labelled N. blackwellii could be grouped together with the type strain of N. farcinica. Three other strains labelled N. farcinica were clearly distinct from this group of 10 strains. A strain of N. asteroides used previously as reference strain for this species was clearly distinct from the N. farcinica strains, and this applied also to a recently proposed reference strain of N. asteroides. A strain of N. brasiliensis was clearly distinct from all the other strains, while the results obtained with a strain received without species designation were inconclusive. On this basis, the authors consider that all the 10 strains, which form a homogeneous group, should be classified as N. farcinica. The 3 other strains labelled N. farcinica should be classified into 2 other species. Nocardia asteroides would seem to be a separate species.