Release of Intracellular Solutes by Four Soil Bacteria Exposed to Dilution Stress

The physiological mechanisms utilized by soil bacteria for acclimation to sudden increases in soil water potential are poorly understood. In this study, we examined the physiological responses of soil isolates of Pseudomonas chlororaphis, P. fluorescens, Bacillus pumulis, and Streptomyces griseus to a sudden increase in solution water potential (dilution). Bacterial isolates were cultured at a low solute water potential (−3.0 MPa) and subjected to rapid water potential increases of 0.5 to 2.0 MPa. The small amount of protein and DNA released by a 2.0 MPa dilution suggests that water potential increases up to 2.0 MPa did not cause significant cell lysis. In response to dilution, intracellular solutes were released into the extracellular environment rather than polymerized into osmotically less‐active compounds or catabolized to CO2 In general, the Gram‐positive isolates B. pumulis and S. griseus were more tolerant to dilution than the Pseudomonas spp., since dilution had no effect on culturability, and the amount of solutes released was small (