Differential expression of thermophilic phosphatases in the wild type and auxotrophic mutant strains of Thermoactinomyces vulgaris.

In the wild type strain (stock no. 1227) of Thermoactinomyces vulgaris, as reported earlier [Sinha and Singh (1980) Biochem. J. 190, 457-460], all phosphatase isoenzymes (three alkaline - AlpI, AlpII and AlpIII, and one acidic - Acp) are present. However, the auxotrophic mutants, the strains 1286 (thi(-)), 1279 (nic(-), ura(-)) and 1278 (thi(-), ura(-)) exhibited two alkaline phosphatase isoenzymes (AlpII and AlpIII), but AlpI was lacking. In the strain 1261 (nic(-), thi(-)), only AlpIII was expressed, and AlpI and AlpII isoenzymes were missing. The results suggest that the strains, which require either thiamine (1286 and 1278) or nicotinamide (1279) for their growth, were AlpI(-) mutants; and the strain (1261), which requires both thiamine and nicotinamide for its growth, was AlpI(-)/AlpII(-) double mutant. There was no direct correlation between uracil auxotrophy and the expression of phosphatases. The uniform expression of AlpIII and Acp in all the strains, irrespective of their nutrient requirements, suggest that these constitutive phosphatases are species-specific. The specific activities of the thermophilic acid and alkaline phosphatases were maximum in the wild type strain (1227) of T. vulgaris. The next in phosphatase activity was the strain 1279 (an AlpI(-) mutant), followed by their decrease, in order, in the strains 1286 and 1278 (which were also AlpI(-) mutants); while least activity of these enzymes was observed in the obligate thermophile strain 1261 (AlpI(-)/AlpII(-) double mutant).