Survival of a genetically engineered Pseudomonas putida strain in soil and its potential to conjugatively transfer genes to indigenous soil bacteria
There is an interest in releasing genetically engineered bacteria into the environment as biofertilizers, biological control agents or to remediate contaminated soil. However, there is little information available on the factors affecting the persistence of genetically engineered bacteria or their potential to transfer genes to indigenous soil microorganisms. This study assessed the survival of a genetically engineered Pseudomonas putida strain CR30RNS (pADPTel) in bulk and rhizosphere soil and its ability to transfer genes for atrazine degradation and tellurite resistance to indigenous soil bacteria. The P. putida strain survived for ten weeks in bulk and rhizosphere soil at approximately 106 cfu per g soil. After the plants were harvested, the population of the P. putida strain declined to undetectable levels. However, upon the addition of water and a nutrient solution containing atrazine, the P. putida CR30RNS (pADPTel) population in the rhizosphere soil rebounded to a density of ca. 105 cfu per g soil while the population in bulk soil remained undetectable. The frequency of conjugative gene transfer to indigenous soil bacteria was assessed under laboratory conditions by the use of filter matings. Under optimal conditions a range of 1-10-2 transconjugants per recipient was observed. Recipient bacteria were identified by FAME analysis as Rahnella aquatilis strains. The results indicate that the genetically engineered bacteria survived better in the rhizosphere of canola than in bulk soil, and had the potential to transfer genes to indigenous soil bacteria.
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