- Volume 69, Issue 2, 1971

SUMMARY: A low proportion of zoospores from dark-grown plants of Blastocladiella emersonii encyst if the suspension of zoospores is maintained in darkness, but visible light causes increased encystment. A lag in the response to light is eliminated by incubating spores in darkness prior to exposure. Light-induced encystment is insensitive to cycloheximide, but ceases when illumination ceases. Light has no effect on encystment of zoospores derived from light-grown plants; these will encyst even if kept in darkness.

SUMMARY: A plasmid conferring tetracycline-resistance from a clinical isolate of Staphylococcus aureus (5401) was transferred to a wide variety of other strains by mixed culture in nutrient broth. Strain 609 converted to tet-r by this method could transfer tet-r efficiently (up to 10−3 in 12 h.) to other strains. Co-factor studies on this donor suggested that transfer of tet-r is mediated by phage transduction. However, filtrates of the donor culture contained few particles able to transfer tetracycline-resistance. It is probable that the transfer occurs by short-lived or cell-bound phage particles. Filtrates of the donor strain obtained after induction with mitomycin C were able to transduce tetracycline-resistance, but at low frequency.

The gene(s) for tetracycline-resistance in these strains is probably borne by a plasmid, since they segregate tetracycline-sensitive derivatives. Ultraviolet (u.v.) light-inactivation studies on transduction of tet-r support this conclusion.

SUMMARY: The size of the competent fraction in Bacillus subtilis cultures was calculated from the frequencies of observed and expected double transformants for the two unlinked markers adenine and indole, and compared with that obtained by light-microscopic autoradiography of samples exposed to [3H]thymidine labelled donor DNA. The two methods give similar results. The size of the competent fraction calculated from the frequencies of observed and expected double transformants is independent of the concentration of DNA and time of exposure to transforming DNA. The observed increase in the frequency of transformation with longer periods of exposure of the cultures to DNA was found to be linearly correlated with the amounts of DNA taken up by individual cells, as judged by the number of grains per labelled cell. No important heterogeneity within the competent fraction with respect to the amount of DNA absorbed per competent cell was observed. It was further demonstrated that under conditions in which competence develops (the competence regime), the transformation frequency and the size of the competent fraction increase proportionally, whereas the amount of DNA absorbed per competent cell does not change. This suggests that the efficiency of competent cells to integrate the donor markers is constant during the competence regime, and is, therefore, not a significant factor determining changes in transformability.

SUMMARY: quantitative survey has been made of conidiation mutants in Aspergillus nidulans. Conidiation mutants were 6 to 13 times more numerous than auxotrophic mutants, but growth tests showed that the mutant defect in 85 % of the conidiation mutants was not confined to conidiation. The number of loci specifically involved in conidiation was estimated to be 45 to 150. Mutants were classified according to the stage of the developmental block and also into asporogenous and oligosporo- genous types; 64 % were oligosporogenous, but in further tests, 84 % of the asporogenous mutants were found to be temperature sensitive or slightly leaky, suggesting that many of the loci involved act only as modifiers in conidiation. The largest group of mutants was blocked before conidiophore formation, while many others failed at ill-defined stages of conidiation, suggesting that failure was due to the gradual build-up of metabolic deficiencies. A class of conidial maturation mutants has also been identified.

SUMMARY: The base composition of DNA preparations from 16 strains of staphylococci, belonging to different subgroups, and from 10 staphylococcal phages were determined from the denaturation temperature (T m) and from the buoyant density. The GC (guanine+cytosine) content of the DNA of the strains ranged from 29·3 to 33·9 % (calculated from T m ) and from 28·5 to 34·0 % (calculated from the buoyant density). No significant difference was observed between the GC content of the DNA of the strains of Staphylococcus aureus and S. epidermidis nor between its various biotypes. The mole fraction GC of staphylococcal phage DNA (31·4 to 34·6 % GC) is somewhat higher than the GC content of the DNA of the strains.

SUMMARY: Vesicular-arbuscular mycorrhiza were established in Trifolium parviflorum in culture by inoculation with Endogone spores. In a medium containing 265 mg. phosphorus (P)/l., as CaHPO4 and K2HPO4, infection occurred only when the medium lacked nitrogen (N). In a medium containing only 100 mg. P/l., infection occurred readily in the presence of 0·5 g. KNO3/l.

Calcium monohydrogen phosphate, Ca phytate, Na phytate, Fe phytate, phytin, lecithin and DNA were adequate sources of phosphate for both plant and fungus. Ca phytate and DNA greatly stimulated fungal growth, and DNA also stimulated spore formation, in the agar medium. With Na in the medium infections in the root were sparse. Inositol may serve as a carbon source for Endogone.

Mycorrhizal infection occurred with either FeCl3 or Fe-EDTA in the medium; when so little iron was present that plants grew poorly, there was also little mycorrhizal infection.

SUMMARY: A method is described for determining the sterol requirement of a mycoplasma to permit its classification either among the sterol-requiring Mycoplasmataceae or the sterol-independent Acholeplasmataceae. A filtered washed suspension is inoculated on media with and without various concentrations of cholesterol and the development of growth noted by microscopical examination.

The sterol requirement was determined for three mycoplasmas whose growth on serum-free media for several subcultures had been claimed. Mycoplasma anatis and Bovine Group 7 were found to be sterol-dependent, but Bovine Group 6 grew without sterol, although under certain circumstances promotion of growth by cholesterol was noted through counteraction of an inhibitory effect.

SUMMARY: When Cordyceps militaris is grown in shaking culture in certain media, two large unicellular forms are produced. The walls isolated from these are similar both qualitatively and quantitatively except for their mannose content, one form containing almost twice the amount as the other (17·5 versus 9·6%). Glucose, the predominant monosaccharide obtained by acid hydrolysis, accounts for more than half (52 to 60%) of the weight of the walls. The remainder is composed of galactose (6%), hexosamine (6%), lipid (8 to 10%), and protein (8 to 10%).

Walls of the unicellular forms contain more glucose and protein than those of the filamentous form, but less hexosamine and lipid. Glusulase releases all of the glucose from walls of the filaments, but only half of the glucose from walls of the unicells.