SURVIVAL OF XENORHABDUS-NEMATOPHILUS AND PHOTORHABDUS-LUMINESCENS IN WATER AND SOIL

Strains of Xenorhabdus nematophilus and Photorhabdus luminescens were genetically marked with kanamycin resistance and the xylE gene to aid their detection in water and soil. Following release in river water, c ells declined to undetectable levels in 6 d. In sterile river water, t his decline was enhanced with cells detectable for only 2 d. In steril e Milli-Q purified water, the decline was slower than in either steril e or non-sterile river water. Survival in soil was also restricted wit h cells only detectable for 7 d. These experiments indicated that both X. nematophilus and P. luminescens have limited survival or competiti ve abilities in these environments. The faster decline of populations in sterile river water was unexpected, and the possible formation of s pecialized survival stages was investigated. In sterile water, a non-c ulturable but viable population of cells was detected, indicating that cells may survive longer than anticipated in the environment and rema in undetectable using standard microbiological methods. The implicatio ns of this work to the use of these strains in biological control and the release of genetically-modified micro-organisms is discussed.