Effect of inoculation of a TOL plasmid containing mycorrhizosphere bacterium on development of Scots pine seedlings, their mycorrhizosphere and the microbial flora in m-toluate-amended soil

Abstract

The purpose of this study was to evaluate the influence of introduced bacteria containing a contaminant degrading plasmid on the growth and survival of pine seedlings and mycorrhizosphere microbial flora in contaminated soil. The Pseudomonas fluorescens strain OS81, originally isolated from fungal hyphae in contaminated soil, was supplied with the TOL plasmid pWW0 : :Km (to generate OS81(pWW0: :Km)) and inoculated in humus-soil microcosms with and without pine seedlings mycorrhized with Suillus bovinus. After 3 months of regular treatment with m-toluate (mTA) solutions, the introduced catabolic plasmid was found to be disseminated in the indigenous bacterial population of both mycorrhizosphere and soil uncolonized by the fungus. Transconjugants were represented by bacteria of the genera Pseudomonas and Burkholderia and their number correlated positively with the concentration of mTA applied. Indigenous mTA degrading bacteria with low similarity to Burkholderia species were also enriched in microcosms. They were mostly associated with mycorrhizal soil or fungal structures and virtually absent in microcosms without pines. The total number of Tol bacteria was higher in mycorrhizospheric soil compared with bulk soil. Inoculation with P. fluorescens OS81(pWW0: :Km) had a positive effect on the development of roots and fungus in contaminated soil. Both inoculation with the P. fluorescens OS81(pWW0: :Km) and mTA contamination as well as the presence of mycorrhized pine roots and fungal hyphae had an effect on the microbial community structure of soil as measured by carbon source oxidation patterns. However, the impact of mTA on the microbial community was more prominent. The study indicates that an effect on plant and fungal development can be obtained by manipulating the mycorrhizosphere. Both introduction of the bacterium carrying the degradative plasmid and the plasmid itself are likely to have a positive effect not only on the organisms involved, but also on bioremediation of contaminated soil, a factor that was not directly monitored here. ß

Inferring the genetic network of m‐xylene metabolism through expression profiling of the xyl genes of Pseudomonas putida mt‐2

“…This is of essence, as the biological functionality of a regulatory network is not only based on the whole of on/off switches and rheostatic responses of the promoters involved (Cases and de Lorenzo, 2005), but also on the downstream expression checkpoints. The TOL system offers a suitable experimental model to this end, as the performance of the regulatory network and its implantation within the general physiology of cells is directly connected to the survival of P. putida mt-2 in sites polluted with given aromatic compounds (Ramos et al, 1991;Sarand et al, 2000). This study intends to contribute to sort out such a multifaceted issue.…”

Role of the DmpR-Mediated Regulatory Circuit in Bacterial Biodegradation Properties in Methylphenol-Amended Soils

“…Inverting and shaking before bacterial inoculation vigorously mixed soils and the supplements. Bacteria were pregrown overnight in semirich medium (1/4KSN-MYE [35]) in the presence of 2 mM 2-methylphenol. Cell pellets were resuspended in phosphate-buffered saline, and approximately 10 6 or 10 8 bacterial cells in 50 l were inoculated into soils as indicated.…”

Catabolic mobile genetic elements and their potential use in bioaugmentation of polluted soils and waters

“…From the viewpoint of soil bioremediation it would therefore be more relevant to understand how more recalcitrant pollutants (which accumulate in the environment) can be rapidly removed by spreading the corresponding mobile catabolic genes. The few cases described above, where the indigenous catabolic potential was very low and catabolic gene transfer decreased the degradation time with several months [39] or protected biological life in the soil [42], show however that this plasmid-mediated bioaugmentation could be a feasible strategy under such conditions.…”

“…The overall enhanced degradation of 2,5-DCB in the inoculated and planted soil may have been partially due to this plasmid transfer, but hard evidence was lacking. Sarand et al [42] inoculated a P. £uorescens soil isolate, provided with the TOL plasmid, in soil microcosms with and without pine seedlings, my- corrhized with Suillus bovinus. After 3 months of regular treatment with m-toluate (mTA) the catabolic plasmid was found to be transferred into indigenous bacteria.…”