Rapid and sensitive method for muramic acid determination by high-performance liquid chromatography with precolumn fluorescence derivatization

Determination of amino sugars in environmental samples with high salt content by high-performance anion-exchange chromatography and pulsed amperometric detection

Amino sugars were determined in natural samples, including seawater, using high-performance anion-exchange chromatography with pulsed amperometric detection and a new-off-line sample cleanup procedure. Samples were hydrolyzed with 3 M HCl for 5 h (100 degrees C) and neutralized with anion retardation resin. Before injection, salts and organic contaminants were removed with a strong cation exchanger in the Na+ form. Detection limits for amino sugars were between 1 and 4 nM (signal-to-noise ratio 3), allowing for the first time quantification of amino sugars in seawater without preconcentration. Precision was 2-11% at the 20 nM level. The relatively simple and rapid sample preparation makes it suitable for routine analyses.

Quantification of Frankia Strains and Other Root-Associated Bacteria in Pure Cultures and in the Rhizosphere of Axenic Seedlings by High-Performance Liquid Chromatography-Based Muramic Acid Assay

Application of a high-performance liquid chromatography-based muramic acid assay with precolumn fluorescence derivatization to quantification of root-associated bacteria was studied both in pure cultures and in the rhizosphere of axenic Festuca rubra seedlings. Quantities of muramic acid from acid-hydrolyzed cells of Frankia strains, Streptomyces griseoviridis, Enterobacter agglomerans, Klebsiella pneumoniae, Pseudomonas sp., and Bacillus polymyxa were mostly proportional to the respective cell protein and carbon quantities, but in some strains, culture age and particularly sporulation affected these ratios considerably. The muramic acid/cell protein ratio was generally 2 to 4 times higher in strains of the two actinomycete genera, Frankia and Streptomyces , than in the rest of the strains. Quantification of Frankia strains, S. griseoviridis, E. agglomerans , and Pseudomonas sp. was also attempted from the rhizosphere of F. rubra seedlings which had been inoculated with pure cultured bacteria and incubated briefly. It was possible to quantify Frankia cells by use of the muramic acid assay from both the root and the growth medium, whereas cells of the rest of the bacterial genera could only be detected in the medium. The detection limit for muramic acid was about 10 ng/ml hydrolysis volume, and from the Festuca rhizosphere, 28 to 63% of the muramic acid in the Frankia inoculum was recovered.

Muramic Acid Measurements for Bacterial Investigations in Marine Environments by High-Pressure Liquid Chromatography

Muramic acid, a constituent of procaryotic cell walls, was assayed by high-pressure liquid chromatography in samples from several marine environments (water column, surface microlayer, and sediment) and a bacterial culture. It is used as a microbial biomass indicator. The method gave a good separation of muramic acid from interfering compounds with satisfactory reproducibility. A pseudomonad culture had a muramic acid content of 4.7 � 10 −10 to 5.3 � 10 −10 μg per cell during growth. In natural water samples, highly significant relationships were found between muramic acid concentrations and bacterial numbers for populations of 10 8 to 10 11 cells per liter. The muramic acid content in natural marine water decreased from 5.3 � 10 −10 to 1.6 � 10 −10 μg per cell with increasing depth. In coastal sediments exposed to sewage pollution, concentrations of muramic acid, ATP, organic carbon, and total amino acids displayed a parallel decrease with increasing distance from the sewage outlet. Advantages of muramic acid measurement by high-pressure liquid chromatography are its high sensitivity and reduction of preparation steps, allowing a short time analysis.

Plasma essential amino acids changes in sea-bass (Dicentrarchus labrax) after feeding diets deficient and supplemented in L-methionine

A fishmeal-based reference diet, a soybean-yeast-based methionine (MET)-deficient diet and two MET-supplemented diets were fed to groups of yearling sea-bass, reared in sea-water at 21 +/- 1 degrees C. Levels of most free essential amino acids (EAA) reached a maximum concentration in plasma between 4 and 8 hr after a single meal. Plasma MET level remained very low with the deficient diet, exhibiting by 4 hr a 10-fold reduction when compared to the reference diet, although MET content was divided only by two in the former. Daily MET intake was then maintained under minimum requirement in fish fed the deficient diet. Supplemented MET reached peak level in plasma substantially sooner than the rest of the EAA, indicating faster absorption and degradation when compared to MET incorporated in feed proteins. Evolution of methionine sulfoxide (MSO) levels in plasma after feeding MET-supplemented diets gives evidences that a degradation pathway of MET into MSO exists in sea-bass.