Isolation and characteristics of yeasts able to grow at low concentrations of nutrients

Seven oligotrophic yeasts, which can grow in a 10(4)-fold dilution of malt-yeast-glucose-peptone medium (10(-4) YM), were mainly isolated from soil. These yeasts belong to the Cryptococcaceae. When inoculated at about 10(2) cells/ml in 10(-4) YM, the isolates grew to 1.4 x 10(3)-2.4 x 10(5) cells/ml after 3 days. Some culture collection yeasts fell into three groups according to their growth characteristics in 10(-4) YM, one group showing characteristics of the oligotrophic yeasts. The half-saturation values of uptake by the five isolated oligotrophic yeasts for D-glucose, L-leucine and L-amino acids were 6.0-25.0, 1.7-43.3 and 3.5-21.6 microM, respectively. The oligotrophic yeasts suspended in 10 mM-phosphate buffer (pH 6.0) had high tolerances for starvation, and remained more than 15% viable after 90 days of starvation.