Symbiotic properties of C4-dicarboxylic acid transport mutants of Rhizobium leguminosarum.

The transport of succinate was studied in bacteroids of an effective, streptomycin-resistant strain (GF160) of Rhizobium leguminosarum. High levels of succinate transport occurred, and the kinetics, specificity, and sensitivity to metabolic inhibitors were similar to those previously described for free-living cells. The symbiotic properties of two transposon (Tn5)-mediated C4-dicarboxylate transport mutants (strains GF31 and GF252) were determined. Strain GF31 formed ineffective nodules, and bacteroids from these nodules showed no succinate transport activity. Strain GF252 formed partially effective nodules, and bacteroids from these nodules showed about 50% of the succinate transport activity of the parent bacteroids. Another dicarboxylic acid transport mutant (Dct-), strain GFS5, isolated after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis, formed ineffective nodules. The ability to form ineffective nodules in strains GF31 and GFS5 was shown to correlate with the Dct- phenotype. The data indicate that the presence of a functional C4-dicarboxylic acid transport system is essential for N2 fixation to occur in pea nodules.     

Sedimentation and resuspension in a New England salt marsh

Particulate matter in a salt marsh can undergo repeated sedimentation and resuspension. Sedimentation measured with sediment traps, increases with tidal amplitude in areas with fast tidal currents, but is unaffected by tidal amplitude in areas with slow currents. The total sedimentation of particulate nitrogen in areas with slow tidal currents is three times as large as the gross tidal exchanges of particulate nitrogen between the marsh and coastal waters. Net tidal export of particles by the marsh suggests that sedimentation is more than offset by resuspension. Resuspension of fine (4–40 µm) particles occurs early in the flood tide in tidal creeks with slow currents. This resuspension does not increase with tidal amplitude, suggesting that it is not caused by tidal currents.     

Colorimetric determination of catechol siderophores in microbial cultures

A highly sensitive spectrophotometric method for the selective detection of catechol compounds such as catechol siderophores (e.g., enterobactin) is described. The basis of the method involves the ability of the vicinal aromatic hydroxyl groups under acidic conditions to bring about a reduction of Fe3+ (from ferric ammonium citrate) to Fe2+. Detection of Fe2+ in the presence of Fe3+ is made with 1,10-phenanthroline under previously established conditions. The assay mixture is heated at 60 degrees C for 1 h to accelerate the development of color which is subsequently measured at 510 nm. The Beer-Lambert law is obeyed over the range of 0.16 to 60 microM 2,3-dihydroxybenzoic acid. Compared to the Arnow nitration method, the assay is more responsive, is approximately seven times more sensitive, and is effective with catechols substituted at positions 3 and 4. The method gives positive results with catechols such as DL-DOPA, L-dopamine, (+/-)-epinephrine, and DL-norepinephrine. Very rapid color development is obtained with ascorbic acid and p-diols, while m-diols are poorly detected. Low degrees of reactivity are shown by hydroxylamino and hydroxamate compounds. Phenolic, sulfydryl, indolyl, and quinonyl derivatives do not interfere with the reaction. The method has been adapted to determine catechol compounds in the culture medium of bacterial cells grown at different iron concentrations.     

Effects of toxicants on populations: A qualitative approach II. first order kinetics

System level effects exhibited by a population subjected to a chronic or an acute dose of toxicant are the emphasis of this study. A three dimensional model of a toxicant and a population, with state variables (the population biomass, the concentration of toxicant in an organism, and the concentration of toxicant in the environment) coupled by a linear dose-response function, is analyzed analytically. One of the main results presents sufficient conditions, in terms of a system level parameter, for the persistence, and for the extinction, of a population exposed to a chronic dose of toxicant. When depuration and degradation are negligible processes, the effects of toxicant accumulation associated with an acute exposure of a population are analyzed in some detail. Both persistence and extinction are shown to be viable behavior modes of a population in this biochemical setting.     

Deoxyribonucleic Acid of Adeno-associated Satellite Virus

Staining patterns suggest that in the adeno-associated satellite virion there exist quasi single-stranded regions which are renatured after extraction to exhibit double strandedness.