Survival of rifampin-resistant mutants of Pseudomonas fluorescens and Pseudomonas putida in soil systems

Abstract

The fate of spontaneous chromosomal rifampin-resistant (Rifr) mutants of Pseudomonas putida and Pseudomonasfluorescens in sterile and live organic soil from which they were isolated was studied. In sterile native-soil assays, a Rifr mutant of P. putida showed no decrease in competitive fitness when compared with the wild-type parent. However, mutants of P. fluorescens were of two general categories. Group 1 showed no difference from the wild type in terms of growth rate, competitive fitness, and membrane protein composition. Group 2 showed a slower growth rate in both minimal and enriched media and an altered membrane protein profile. These mutants also demonstrated decreased competitive fitness compared with the wild-type strain. In live soil, the Rif' P. putida strain persisted throughout the 38-day test period with a decay rate of 0.7 log10 CFU/g of soil per 10 days. A group 1 Rifr p. fluorescens mutant maintained its inoculated titer for 7 to 10 days and then decayed at a rate of 0.2 to 0.4 loglo CFU/g of soil per 10 days. A group 2 Rifr P. fluorescens mutant remained at its titer for 1 to 5 days before decaying at a twoto threefold-faster rate. These findings indicate that rifampin resistance may not be an innocuous mutation in some pseudomonads and that marked strains should be compared with wild-type parents before being used as monitors of parental strain survival. Colonization of sterile soil with either the wild-type or mutant strain precluded normal colonization of the second added strain. These results suggest that there are limited sites for colonization of Pseudomonas species in these soils, a finding which may relate to the eventual fate of the introduced organisms.

Fitness of genetically modified Pseudomonas fluorescens in competition for soil and root colonization

“…The population dynamics of both the separate and mixed introduced strains in soil and wheat rhizosphere, i.e. a gradual decline of cfu counts over time, with enhanced numbers of introduced organisms occurring in the rhizosphere (for the mixed introductions), was similar to that often described in other reports of introduced fluorescent pseudomonads [3,[13][14][15][16][17]. Abiotic (e.g.…”

“…This might indicate the second colonizers encountered different colonization sites in soil than the primary colonizers, even though the final soil moisture was kept similar. It is not clear why this was observed in the light of previouslydescribed niche exclusion for P. fluorescens and P. putida strains sequentially added to soil [14].…”

Role of the intraspecific competition in the regulation of Agrobacterium tumefaciens transconjugant population level in soil experiments

“…The ecological disadvantage for a strain which results in its inability to dislodge a primary colonizer, has already been described by Compeau et al [34] in a soil study with a strain of P. fluorescens and a rifampicin-resistant mutant. They showed that the order of inoculation was determinant: the first introduced organism inhibited the development of the challenging one.…”

Survival in soil of genetically engineered Escherichia coli as related to inoculum density, predation and competition

“…Altern.~tive!y, the higher final density of the wild-type isolate may have prevented the increase in number of the challenging engineered strain. Pseudomonas fluorescens derivatives harboring either chromosomal Tn5 insertions or rifampin mutations also exhibited a decreased ability, to colonize sterile soil when competing with their isogonic counterpart [39,40]. 32 days after the mixed inoculation in sterile microcosms, the addition Of a protozoa-free microflora led to a decline of both E. coil populations densities ( Fig.…”