Differential tolerance of Pseudomonas putida biofilm and planktonic cells to desiccation

Abstract

The desiccation tolerance of Pseudomonas putida strain mt-2 cells within intact unsaturated biofilms and cells cultivated in liquid media was examined. Since as soils dry there can be an increase in the solute potential and reductions in nutrient availability, we also assessed the effect of the solute and matric (low-water-content) components of the total water potential, and nutrient availability on cell survival. Biofilms were cultivated in model laboratory systems that can simulate the matric and solute components of the total water potential and the poorly mixed nature of unsaturated habitats. Desiccation stress was imposed by exposing biofilm and planktonic cells to environments with controlled relative humidities. Our results show that biofilm cells are more tolerant to air drying than are planktonic cells, and tolerance is enhanced when there is an adequate supply of nutrients available to the cells. We provide evidence suggesting that a major factor contributing to desiccation sensitivity is the matric stress itself rather than solute stress and that matric stress is inherently more stressful to P. putida than is the thermodynamically equivalent solute stress.