Role of Chemotaxis in the Ecology of Denitrifiers

A modification of the Adler capillary assay was used to evaluate the chemotactic responses of several denitrifiers to nitrate and nitrite. Strong positive chemotaxis was observed to NO₃⁻ and NO₂⁻ by soil isolates of Pseudomonas aeruginosa, Pseudomonas fluorescens, and Pseudomonas stutzeri, with the peak response occurring at 10⁻³ M for both attractants. In addition, a strong chemoattraction to serine (peak response at 10⁻² M), tryptone, and a soil extract, but not to NH₄⁺, was observed for all denitrifiers tested. Chemotaxis was not dependent on a previous growth on NO₃⁻, NO₂⁻, or a soil extract, and the chemoattraction to NO₃⁻ occurred when the bacteria were grown aerobically or anaerobically. However, the best response to NO₃⁻ was usually observed when the cells were grown aerobically with 10 mM NO₃⁻ in the growth medium. Capillary tubes containing 10⁻3 M NO₃⁻ submerged into soil-water mixtures elicited a significant chemotactic response to NO₃⁻ by the indigenous soil microflora, the majority of which were Pseudomonas spp. A chemotactic strain of P. fluorescens also was shown to survive significantly better in aerobic and anaerobic soils than was a nonmotile strain of the same species. Both strains had equal growth rates in liquid cultures. Thus, chemotaxis may be one mechanism by which denitrifiers successfully compete for available NO₃⁻ and NO₂⁻, and which may facilitate the survival of naturally occurring populations of some denitrifiers.     

The role of metal ions in chemical evolution: Polymerization of alanine and glycine in a cation-exchanged clay environment

Summary The effect of the exchangeable cation on the condensation of glycine and alanine was investigated using a series of homoionic bentonites. A cycling procedure of drying, warming and wetting was employed. Peptide bond formation was observed, and the effectiveness of metal ions to catalyze the condensation was Cu²⁺ > Ni²⁺ Zn²⁺ > Na⁺. Glycine showed 6% of the monomer incorporated into oligomers with the largest detected being the pentamer. Alanine showed less peptide bond formation (a maximum of 2%) and only the dimer was observed.     

Binding of nickel (II) to 5′-nucleoside monophosphates and related compounds

Summary The interactions of Ni(II) cation with a representative suite of purine bases and the respective nucleosides and nucleotides have been studied by ultraviolet difference spectroscopy. Apparent association constants, K_app, were determined for each system at pH 7.0, using computer linear regression coupled with an iteration technique. The specificity of binding of Ni²⁺ for the purine nucleotides studied at pH 7.0 was 5-GMP > 5-IMP > 5-AMP; a similiar ordering was also found for the respective nucleosides and bases. In this study binding was not observed for the suite of pyramidines used, although a Ni²⁺ - cytidine complex has been observed (Fiskin and Beer, 1965). It was also found that Ni²⁺ bound more strongly to the purine 5-nucleotides than to the respective nucleosides and bases. These trends are explained in terms of metal-ligand bonds and available bonding positions on the ligands. A role for metal-ion-nucleotide types of complexes is suggested in the processes that might have given rise to the origin of life.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.