Growth response of Nitrosomonas europaea to amino acids

Growth responses of Nitrosomonas europaea to individual amino acids or vitamins was observed in log-phase cultures, as was the incorporation of carbon-14 labeled amino acids. Nitrite formation and protein synthesis were increased by l-glutamic acid, l-aspartic acid, l-serine, and l-glutamine. l-Lysine, l-histidine, l-threonine, l-valine, l-methionine, and l-arginine were inhibitory. The other amino acids had no effect on growth. All of the uniformly labeled amino acids added at low concentrations were taken up by growing cells and distributed into cell fractions. From 1 to 12% of the added radioactivity was present in cells analyzed in late log phase, depending on the amino acid; glycine and l-serine caused accumulation of the label to the greatest extent, whereas l-aspartic and l-glutamic acids were among those incorporated to the least extent. Aspartic acid increased both cell protein and nitrite values, but did not alter the ratio of protein to nitrite from that found in controls.

Uptake and utilization of amino acids by resting cells of Nitrosomonas europaea

Incorporation of selected amino acids by resting cells was studied with regard to effects of concentration, rate and extent of incorporation, cellular distribution, effect of ammonium ion on uptake, and competitive effects. l-Aspartic acid, l-alanine, l-serine, and glycine presented at trace levels were incorporated at rates ranging from 0.11 to 8.2 mumumoles per mg (dry weight) per minute, and maximal incorporation was 11 to 333 mumumoles per mg (dry weight). When glycine and aspartic acid were supplied at substrate level, the rate of incorporation increased 14- and 109-fold, respectively. The presence of ammonium ion further increased both the rate and extent of uptake of glycine and aspartic acid. The distribution of cellular radioactivity arising from (14)C amino acids indicated that cell pool radioactivity was concentrated from 1.2- to 24.5-fold over the external medium. Aspartic acid pool radioactivity accounted for 50% or more of the total cellular radioactivity, whereas radioactivity in glycine and serine pools dropped from initially high levels to 20 to 25% during incubation. The decrease in pool radioactivity with both glycine and serine was accompanied by an increase in other fractions, especially in the cell residue. The growth-inhibiting amino acid l-valine, supplied at substrate level, contributed more carbon per milligram (dry weight) than any other amino acid studied. l-Leucine, in the presence of l-valine, was observed to decrease valine incorporation.

Effect of mixed culture on Nitrosomonas europaea simulated by uptake and utilization of pyruvate

Clark, Connie (University of Minnesota, Minneapolis), and E. L. Schmidt. Effect of mixed culture on Nitrosomonas europaea simulated by uptake and utilization of pyruvate. J. Bacteriol. 91:367-373. 1966.-Contamination of a 5-liter culture of Nitrosomonas europaea resulted in enhanced nitrite formation as compared with pure cultures. The dominant contaminant, a yellow-pigmented, heterotrophic bacterium, was isolated and studied both in pure culture and in deliberate mixture with N. europaea. Growth of N. europaea was stimulated in mixed cultures with the heterotrophic isolate to varying degrees, apparently depending on the age and density of autotrophic inocula. Mixed culture stimulation of N. europaea was evidenced only by a shortened lag phase, since post-lag phase growth of the autotroph was equivalent in both pure and mixed cultures. The heterotrophic component had a nutritional requirement for amino acids when grown on simple media; presumably, in the mixed culture system, the heterotroph was provided with amino acids synthesized by the autotroph. The mixed culture effect was reproduced in all essential features by the addition of sodium pyruvate to the nitrification medium. Pure cultures of N. europaea were shown to incorporate sodium pyruvate-2-C(14) during growth. Labeled carbon was widely distributed in cell fractions. The more pronounced and consistent pyruvate effect was observed on old inocula of N. europaea.