The adnA transcriptional factor affects persistence and spread of Pseudomonas fluorescens under natural field conditions.

A soil plot was inoculated with a mixture of Pseudomonas fluorescens Pf0-2, the wild type, and Pf0-5a, a Tn5 insertion mutant in adnA, at 7.84 log CFU/g of soil. Over a period of 231 days, culturable populations of both strains were measured at selected times below and away from the point of inoculation. Pf0-5a did not spread as fast and attained significantly lower populations than Pf0-2. At sample depths below the inoculation site, the adnA mutant showed a significant decrease in CFU/g of soil as compared to Pf0-2. Pf0-2 was first detected at the 1.5-cm annular site at 3 days after inoculation, whereas Pf0-5a required 7 days to travel the same distance. At this distance, the wild-type strain could be detected at a 21.5- to 25-cm depth, whereas Pf0-5a could be detected only as deep as 15.5 to 18 cm. At 4.5 cm from the site of inoculation and in soil fractions corresponding to 13 to 18 cm, Pf0-2 was the only strain detected. These results suggest that the transcription factor AdnA provides a fitness advantage in P. fluorescens, allowing it to spread and survive in soil under field conditions.