Nitrogen assimilation tests

L. J. Wickerham, J. Bacteriol., 52 293-301 (1946). A critical evaluation of the nitrogen assimilation tests commonly used in the classification of yeasts. 

Assimilation tests for carbon compounds use yeast nitrogen base (YNB) without carbon sources, and the assimilation test for nitrogen compounds use yeast carbon base (YCB) without assimilable nitrogen sources. For the tests described, YNB without amine acids and ammonium sulfate is used (Anonymous, 1984). Carbon sources normally examined include a number of pentoses, hexoses, disaccharides, trisaccharides, polysaccharides, alcohols, organic acids, and glycosides as specified by Yarrow (1998). Nitrogen sources commonly tested include nitrate, nitrite, ethyl-amine hydrochloride, cada-verine dihydrochloride, L-lysine, imidazole, glucosamine, creatine, and creatinine. When nitrite is used as a test compound, it is necessary to adjust the pH of the medium to 6.5 because toxic nitrous acid is formed at pH <6.0. 

The nitrogen flow model was tested for sensitivity to varying the "biological parameters" of filter-feeder electivity and assimilation efficiency. Results detailed in Wickens Field (1985) show that the model is not sensitive to varying biological parameters when the system is closed (i.e. no water transport through upwelling or... 

Assimilable nitrogen sources readily utilized by all the tested strains were peptone, hydrolysed casein, yeast extract, glutamic acid. 

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