Assimilation of Carbon and Nitrogen

The ability or inability of an isolate to oxidatively utilize (assimilate) single sources of carbon or nitrogen in media otherwise devoid of carbon or 

Only young, vigorously growing cultures should be used for the evaluation of nitrogen and carbon utilization profiles. Furthermore, cultures should be previously transferred from yeast extract-malt extract medium 

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 determination of carbon and nitrogen utilization profiles can be performed in broth or pour plates seeded with the microorganism of interest. Success using these techniques require that fungi be in pure culture and that carbon and nitrogen sources be free of contamination. To interpret the broth method (Anonymous, 1984), a finely ruled white index card is placed behind the tube and the degree to which haze/turbid-ity hampers visualization is noted. Relative growth may be scored as follows  

Lines on card clearly visible and no increase in turbidity (—) 

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