Death of Pseudomonas aeruginosa in soil.

When incubated in natural (nonsterilized) soil, Pseudomonas aeruginosa died initially at a rate which approximated the rate for starvation of a pure culture in buffer. Predation by other soil microbes or phage did not appear to be involved, and pyocyanin either was not produced or was ineffective. The initial rate of death was followed by a second, considerably slower rate. Cells initially added in low numbers to soil also underwent biphasic death as above. Slow drying of the soil caused a period of rapid soil death of P. aeruginosa, but this then slowed to give residual numbers and a death rate similar to the second death rate noted for soil not allowed to dry. The cells in the dry soil had not changed genetically to a desiccation-resistant form. Pseudomonas aeruginosa died out completely in a relatively short time when the soil was first quickly dried to a water content similar to that obtained initially through slow drying and then further allowed to dry slowly. These observations appear to point to a dormant form, in some ways resembling a cyst, for P. aeruginosa in soil.