Figure 1.

Cell viability and phosphatase activity. A, Viability of the lpb1 mutant and wild-type cells after 1 week of growth on solid medium devoid of phosphate. The arrow denotes the bleached lpb1 colony. B, Qualitative analysis of phosphatase activity secreted by wild-type cells (wt), the lpb1 mutant, and the psr1 mutant. The psr1 strain represents a negative control; the mutant is unable to synthesize alkaline phosphatase in response to P deprivation (Wykoff et al., 1999). Cells were streaked onto TA solid medium prior to spraying the plates with the colorimetric phosphatase substrate 5-bromo-4-chloro-3-indolyl-P, which turns blue after phosphate is cleaved from the molecule by alkaline phophatase. The plates were allowed to develop for 2 h before recording the results.