TABLE 1

pH regulates white-to-opaque switching in strains with different backgroundsa

StrainCulture conditionWhite-to-opaque switching frequency (%) at pH:
5.06.07.07.58.0
WO-1 (FC4, α/α)Air29.1 ± 4.8*2.9 ± 0.92.3 ± 0.23.0 ± 0.53.5 ± 0.2
5% CO2100.0100.0*69.4 ± 7.549.5 ± 13.466.8 ± 3.4
SN250α (α/α)Air19.7 ± 8.415.9 ± 2.215.3 ± 8.412.8 ± 7.6NA
5% CO290.3 ± 7.882.4 ± 25.7*27.7 ± 21.518.3 ± 2.4NA
12C (a/a)Air<0.5<1.0<0.5<0.5<0.4
5% CO222.3 ± 5.9*13.0 ± 12.2*<1.0<1.51.0 ± 1.8
P37005 (a/a)Air<0.3<1.0<0.4<0.5<1.0
5% CO22.7 ± 0.6*1.3 ± 0.5<0.5<0.4<0.4
  • a Two α/α strains (strain FC4, a stock of WO-1, and strain SN250α) and two a/a strains were used. White cells were plated onto Lee's glucose medium plates and incubated in air or 5% CO2 at 25°C for 7 days. Assays for the quantitation of the white-to-opaque switching frequencies were performed. <, no opaque colonies or colonies with opaque sectors were observed. *, the switching rate is significantly (Student's t test, P < 0.05) higher than that under the condition at the next higher pH. For example, the switching rate of strain WO-1 at pH 5.0 (29.1 ± 4.8) was significantly higher than that at pH 6.0 (2.9 ± 0.9). NA, not available.