- Volume 14, Issue 2, 1956

SUMMARY: A study has been made of conditions affecting the production of antibiotics in three soils by a number of unidentified Streptomyces spp. capable of inhibiting a variety of test organisms in vitro. In actinomycete-inoculated soils, antibiotic production was demonstrated only in sterile soils supplemented with a suitable organic source. The greatest accumulations of antibiotics were found in a neutral soil with added glucose (2·5%) while under similar conditions, no antibioties, or only traces were recovered from acid and alkaline soils. Antibiotics, however, could be recovered from inoculated acid soil, following neutralization and the addition of glucose. Fresh grass (3%), clover (3%) and soybean meal (2%) were also suitable supplements for antibiotic production by the majority of the actinomycetes, though the amounts of antibiotics were considerably less than in glucose-treated soils.

In greenhouse experiments the assessment of root damage to wheat seedlings in sterile soil demonstrated that all the actinomycetes tested significantly reduced the degree of root-rot caused by Helminthosporium sativum. In the neutral and alkaline soils a relationship was evident between disease incidence and degree of antagonism exhibited by actinomycetes in vitro, suggesting that antibiotics were responsible. No such relationship was observed between disease control and the antibiotic-producing abilities of the actinomycetes in soil as determined by standard assay procedures.

SUMMARY: Clupein at 0·02–0·05% in the liquid nutrient medium used to cultivate nodule bacteria, rapidly killed the bacteria and slowly inactivated a bacteriophage that attacked them. When added to a bacterial culture in liquid medium before adding phage, clupein prevented phage and bacteria from combining; when added after the two had combined, clupein interrupted further stages of phage-host interaction. Clupein at 0·0016% acted bacteriostatically and slowed phage multiplication but did not stop it.

Trypsin and chymotrypsin hydrolyse clupein, trypsin breaking about twice as many peptide bonds as chymotrypsin. At a concentration corresponding to 0·02–0·05% clupein, the peptides produced by chymotrypsin acted bacteriostatically in the liquid nutrient medium; the peptides inactivated phage much more slowly than did intact clupein, and they inhibited phage multiplication by interfering with the combination between phage and host. When added after phage and bacteria had combined, the peptides did not interfere with further stages of phage-host interaction. The smaller peptides produced by trypsin had no effect on host bacteria, phage, or phage/host interaction.

Phage preparations partially inactivated by clupein had their activity partially restored by incubation with trypsin or chymotrypsin.

Clupein, but none of its hydrolytic products, made phage with much non-phage material sedimentable by slow-speed centrifugation.

SUMMARY: When extracts from plants infected with various strains of tobacco mosaic virus were ultracentrifuged, the non-infective supernatant fluids still contained 0·5-5% of the protein serologically related to the viruses. The small, mostly spherical, particles aggregated to form short rods as the antigen was progressively purified by precipitation with acid or salts. It formed long rods when heated in pH 5·5 buffer or when incubated with trypsin. As the particles increased in length, their serological behaviour in precipitation tests changed from ‘somatic’ to ‘flagellar’ type.

Purified preparations of the unsedimented antigen from plants infected with either of two virus strains contained 0·1–0·2% phosphorus, seemingly in the form of a ribose nucleic acid. No evidence was obtained that the preparations were mixtures containing some particles with the 0·5% phosphorus characteristic of infective virus and some particles of protein free from nucleic acid.

One virus strain produced a higher ratio than the others of unsedimented to sedimented antigen. The amount of unsedimented antigen was correlated with the total content of anomalous protein when the protein was increasing rapidly, but later it fluctuated unpredictably. No conditions were found that consistently favoured its accumulation, but when plants systemically infected with the type strain were kept at 36 °, the total amount of antigen decreased, while the amount unsedimented sometimes increased.

The proportion of the total antigen now obtained as poorly infective nucleoprotein is much less than 10 years ago, when a third of it sedimented in the ultracentrifuge but failed to compact into a pellet. Now the uncompacted sediment, with all the host plants and virus strains used, contains only a trivial part of the total antigen. The virus released into sap when leaves are minced is, weight for weight, more infective than the virus that remains in the leaf residues until it is released by fine grinding.

SUMMARY: The urease activity of Corynebacterium renale has been studied in washed suspensions and in cell-free extracts of the micro-organism. The urease is constitutive, and whole organisms have a urease activity of 17,000-22,000μg. NH3/mg. dry wt. organisms/hr. in 0·5m-urea in phosphate buffer at pH 7·0. In a cell-free extract the enzyme is optimally active at pH 7·5, has a Michaelis constant of 0·030m, and a temperature velocity constant of 7800 cal.; the activity is inhibited by atmospheric oxygen and by thiourea, but not by sixteen other analogues of urea tested.

SUMMARY: A new Saccharomyces species has been isolated from soil. It is distinguished from other species of the genus by its ability to ferment glucose, galactose, sucrose, maltose and raffinose 1/3, as well as by its small cells and the formation of protuberances resembling conjugation tubes during sporulation.