Additional Nucleotide Sequences in Precursor 16S Ribosomal RNA from <Emphasis Type="Italic">Escherichia coli</Emphasis>

MATURE 5S, 16S and 23S ribosomal RNA species present in E. coli ribosomes are the end products of complex biosyn-thetic pathways. They are formed by reduction in length, and methylation of longer RNA chains transcribed on the ribosomal RNA cistrons of E. coli DNA. While these modifications take place the ribosome structure is formed by progressive addition of ribosomal proteins and conformational changes in the resulting ribonucleoprotein precursor particles¹.     

The nature of the microbial stimulus affecting sporophore formation in Agaricus bisporus (Lange) Sing

An apparatus is described in which pure cultures of Agaricus bisporus were maintained on composted media in filtered atmospheres free from (a) noxious concentrations of carbon dioxide, and (b) contaminating microorganisms. When grown on compost alone, cultures of A. bisporus did not produce sporophores. Their formation was however stimulated by a covering layer of an unsterilized mixture of peat and chalk (=‘casing’ soil). Autoclaving or fumigating ‘casing’ with propylene oxide decreased populations of contaminating bacteria and prevented sporophore formation. Populations of micro-organisms isolated from unsterile ‘casing’ contained bacteria which when added to pure cultures of A. bisporus stimulated fruit-body formation. Numbers of these stimulators increased when cultured on a carbon-free liquid medium exposed to atmospheres with ethanol, ethyl acetate and acetone or containing the volatile metabolites of A. bisporus. The ability to utilize these volatile chemicals was exploited in a selective technique for isolating sporophore stimulators where aqueous suspensions of mixed bacterial populations were exposed to atmospheres of these materials for 5 days, before aliquots were added to agar media subsequently gelled. The stimulatory bacteria were identified as, or closely related to, Pseudomonas putida.     

The DNA of Acanthamoeba spp.; A Method for Extraction and Its Characterization

SYNOPSIS. A method is described which permits the recovery of a high yield of undegraded DNA from Acanthamoeba castellanii. The DNA of A. castellanii is comprised of 2 species: the buoyant density of the major component is 1.720 and of the minor component, 1.693. The renaturation characteristics of the minor component suggest that it is of mitochondrial origin. Two components are also present in the DNA of A. palestinensis, A. polyphaga and A. astronyxis. The buoyant densities of major and minor components differ between species.     

Attempts to Displace the Indigenous Antibiotic Resistant Gut Flora of Chicken by Feeding Sensitive Strains of Escherichia coli Prior to Slaughter

Attempts to limit the use of antibiotics have not, in general, resulted in the gut flora in farm animals becoming predominantly sensitive. Partial success has been demonstrated, however, by feeding chickens with antibiotic sensitive Escherichia coli known to be good colonizers of the chicken gut. Where feeding was done prior to slaughter a corresponding reduction in carcass contamination by resistant E. coli was observed.     

Effects of some systemic imidazole and triazole fungicides on white clover and symbiotic nitrogen fixation by Rhizobium trifolii

Effects of prochloraz, imazalil, diclobutrazol, triadimefon and propiconazole were studied. Compared with most systemic fungicides previously tested they were all relatively toxic to R. trifolii on agar. Effects of soil residues of the compounds on the growth and nitrogen fixing capacity of white clover were measured. The lowest concentration of the fungicides used was that which would be present if all the active ingredient from a single application remained unchanged and evenly distributed in the top 5 cm of soil. This concentration of diclobutrazol decreased the size and weight of 11-wk-old clover plants. The rate of nitrogen fixation was reduced by twice this concentration and root nodulation by four times this amount. None of the other fungicides had any significant effect. The possibility of field application of diclobutrazol to cereals causing damage to clover crops is discussed. It is questionable whether harmful soil residues will ever accumulate from normal usage of the fungicide but exceeding the recommended rate of application, or application to cereals undersown with clover, might cause undesirable effects on the clover.     

The effect of oxamyl on the growth of peas attacked by pea cyst nematode

Oxamyl treatment at drilling greatly increased the growth of the plants, the yield and quality of the peas harvested, in soil infested by small or large numbers of Heterodera goettingiana. Treated plants were continuing to set pods when non-treated plants were senescing. Rhizobium nodulation, sap nitrate and tissue nitrogen content were increased in treated plants. Oxamyl applied to growing plants reduced later nematode invasion and enabled root nodulation to proceed with an increase in tissue nitrogen but no increase in yield. Oxamyl applied at drilling in April was inactive against invasion by H. goettingiana in June, which enabled the nematode to multiply equally in treated and non-treated plots. The most economic treatments were at the smallest rates, giving the greatest increase in yield/kg of oxamyl applied.