MOISTURE REQUIREMENTS OF BACTERIA

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Abstract
As aw (water activity) was lowered from a favorable aw by the addition of KC1 the apparent lag phase and the generation time of P. fluorescens were progressively lengthened, at any one temperature, until growth was prevented. As the temperature was dropped below the optimum, the lower limit of aw for growth was raised progressively. The apparent lag phase and the generation time were also proportionately longer at low values of aw than would be expected for the drop in temperature. The tolerance to low aw was less at unfavorable pH values than within the optimum pH range. The apparent lag phase and the generation time were longer at the adverse pH values than within the optimum pH range. When both the pH and the temperature were made unfavorable, the lower limit of aw for growth was higher than if only one condition was made adverse. The apparent lag phase and the generation time were lengthened by the combination of these two factors to a greater extent than if only one factor was made adverse.