Persistence of Pseudomonas aureofaciens strains and DNA in soil

Persistence of a 630-bp fragment of a Tn7-lac fusion element inserted chromosomally in Pseudomonas aureofaciens Ps3732RNL11 was assessed in non-autoclaved and autoclaved sandy loam soil. PCR-amplified 630-bp DNA fragments, from DNA extracts of inoculated, non-autoclaved soil, were observed at 2 and 4 wk after inoculation. DNA extracts of inoculated, autoclaved soil subjected to PCR yielded the expected 630-bp DNA bands at 2, 4, 8, 12, 18 and 24 wk after inoculation. Our results showed that extracellular DNA can persist in soil for extended periods. Survival of P. aureofaciens Ps3732RNL11 and Ps3732RN (parental wildtype) in soil was assessed over 44 wk. After 30 wk in non-autoclaved soil, Ps3732RNL11 and Ps3732RN cells initially inoculated into soil at log 4.3 and log 4.1 cells g−1 dry soil, respectively, were not detectable by viable plating. Ps3732RNL11 and Ps3732RN cells inoculated at log 8.1 and log 7.9 cells g−1 dry soil, respectively, were detectable by plating after 44 wk.