Temperature-dependent survival of isolates ofThiobacillus ferrooxidans

Abstract

Psychrotrophic and mesophilic isolates ofThiobacillus ferrooxidans were examined for their ability to survive at temperatures above the T_max, below the T_min, and at −15°C after a slow freeze. There were no thermoduric strains among those studied; the viable counts decreased by two to five orders of magnitude in 24 h, following exposure to a supermaximum temperature (2–4°C above the T_max). Strain F1, when exposed to progressively higher temperatures, predictably showed increasingly rapid rates of death. When strain S2 was exposed to 2°C, a temperature below its T_min but still above freezing, there was little change in the viable counts over the 38-day observation period. When the various strains were subjected to a slow freeze at −15°C, the cells died quite rapidly with the percentage survival among the strains varying from .0006% to .0155% after 24 h. A survival curve for strain A1 showed that the number of viable cells decreased by approximately three orders of magnitude in the first 4–6 h, and a further three orders of magnitude over the next 40 h.