Deoxyribonucleic acid modification by intermediate-type modification mutants of Escherichia coli K-12 and B.

The modification of bacteriophages grown on r-m+/- restriction and modification mutants of Escherichia coli K-12 or B appears to be related to the number of restriction-specific sites in the viral genome. Bacteriophage fd and its mutant U1 fd, which carry two and one B-specific sites, respectively, are not modified in vivo by rB-mB+/- mutant strains. In vitro treatment of fd RF-B+/- deoxyribonucleic acid (DNA) or U1 fd RF-B+/- DNA by endo R-Eco B results in cleavage of the substrate DNA. Lambda bacteriophage, after growth in r-m+/- mutant host strains (lambda-K+/- or lambda-B+/-), is partially protected from in vivo degradation by wild-type homospecific strains. Its efficiency of plating on these strains is approximately 10(-2). However, a hybrid phi80-lambda phage which carries only one K-specific site (sklambda-1) is not modified by rK-mK+/- strains. Labeled DNAs from lambda-B+/- and lambda-K+/- phages were used as substrates for endo R-Eco B and endo R-Eco K nucleases. Zonal centrifugation analysis of the products of the reactions indicate that rK-mK+/- mutants do not protect lambda DNA from in vitro degradation by endo R-Eco K. In contrast, rB-mB+/- mutants appear to partially protect lambda DNA from attack by endo R-Eco B.     

Molecular cloning of an Escherichia coli plasmid determinant than encodes for the production of heat-stable enterotoxin.

A conjugative plasmid, ESF0041 was isolated from an enterotoxigenic strain of Escherichia coli from calves. ESF0041 was found to be 65 x 10(6) daltons in mass of a member of the F incompatibility complex. Acquisition of ESF0041 by E. coli K-12 was invariably associated with the capacity to produce heat-stable (ST) enterotoxin. ESF0041 and pSC101 deoxyribonucleic acids were cleaved with EcoRI, and the fragments were ligated with polynucleotide ligase. Transformation of E. coli K-12 with the ligation mixture led to the isolation of an ST+ clone. Further analysis of the plasmid deoxyribonucleic acid from this clone showed that a structural gene(s) associated with ST biosynthesis had been isolated as a 5.7 x 10(6)-dalton ESF0041 fragment in pSC101. In turn, 5.7 x 10(6)-dalton fragment was ligated to a multicopy COLE1 derivative, RSF2124, so that toxin synthesis was amplified about threefold.     

Ligation of EcoRI endonuclease-generated DNA fragments into linear and circular structures.

Double-stranded DNA fragments terminated at their 5′-ends by the singlestranded sequence pA-A-T-T-, generated by digestion of DNA with EcoRI restriction endonuclease, were ligated with Escherichia coli polynucleotide ligase under various conditions of temperature, concentration and time. The linear and circular products of ligation were separated by electrophoresis in agarose gel and quantitated by densitometry. The rate of ligation of (EcoRI-cleaved) simian virus (SV40) DNA at a concentration of 100 μg/ml increased from 0 °C to 5 °C to 10 °C (6-fold increase overall); raising the temperature to 15 °C did not further increase the rate of ligation. At the appropriate DNA concentrations, the predominant products of ligation are either linear concatemers that are integral multimers of the starting DNA fragment, or covalently closed circular structures of the monomeric DNA fragment. Ligating a mixture of two different length DNA fragments gives rise to all of the possible expected recombinant molecules.Linear or circular products of ligation were predicted by consideration of the total concentration of DNA termini, i, and the local concentration of one terminus in the neighborhood of the other on the same DNA molecule, j. The parameter j is a function of the length of a DNA molecule, providing this length is greater than the random coil segment of DNA. Experimentally it was found that circular structures are formed in significant amounts only under conditions when the value of j is several times greater than that of i. When j = i, equal amounts of linear and circular products would be expected, but most of the molecules were ligated into linear concatemers. No circular structure of a DNA fragment whose contour length l (6 × 10⁻² μm) is smaller than the random coil segment value b (7·17 × 10⁻² μm) was observed, while circular structures of the dimer of the same molecule (12 × 10⁻² μm) were detected.     

Acetylene reduction (nitrogen fixation) and metabolic activities of soybean having various leaf and nodule water potentials

An apparatus was designed that permitted acetylene reduction (N₂ fixation) by root nodules to be measured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least 5 hours, except for the first 30 to 60 minutes. Endogenous ethylene production did not affect the measurements. Successive determinations of acetylene reduction could be made without apparent aftereffects on the plant.     

Comparing urban food system characteristics and actions in US and Indian cities from a multi‐environmental impact perspective: Toward a streamlined approach

Food action plans in many global cities articulate interest in multiple objectives including reducing in‐ and trans‐boundary environmental impacts (water, land, greenhouse gas (GHG)). However, there exist few standardized analytical tools to compare food system characteristics and actions across cities and countries to assess trade‐offs between multiple objectives (i.e., health, equity) with environmental outcomes. This paper demonstrates a streamlined model applied for analysis of four cities with varying characteristics across the United States and India, to quantify system‐wide water, energy/GHG, and land impacts associated with multiple food system actions to address health, equity, and environment. Baseline diet analysis finds key differences between countries in terms of meat consumption (Delhi 4; Pondicherry 16; United States 59, kg/capita/year), and environmental impact of processing of the average diet (21%, 19%, <1%, <1% of community‐wide GHG‐emissions for New York, Minneapolis, Delhi, and Pondicherry). Analysis of supply chains finds city average distance (food‐miles) varies (Delhi 420; Pondicherry 200; United States average 1,640 km/t‐food) and the sensitivity of GHG emissions of food demand to spatial variability of energy intensity of irrigation is greater in Indian than US cities. Analysis also finds greater pre‐consumer waste in India versus larger post‐consumer accumulations in the United States. Despite these differences in food system characteristics, food waste management and diet change consistently emerge as key strategies. Among diet scenarios, all vegetarian diets are not found equal in terms of environmental benefit, with the US Government's recommended vegetarian diet resulting in less benefit than other more focused targeted diet changes.