Impact of wild-type and genetically modified Pseudomonas fluorescens on soil enzyme activities and microbial population structure in the rhizosphere of pea

The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1046/j.1365-294x.1998.00367.xThe aim of this work was to determine the impact of wild type along with functionally and non-functionally modified Pseudomonas fluorescens strains in the rhizosphere. The wild type F113 strain carried a gene encoding the production of the antibiotic 2,4 diacetylphloroglucinol (DAPG) useful in plant disease control, and was marked with a lacZY gene cassette. The first modified strain was a functional modification of strain F113 with repressed production of DAPG, creating the DAPG negative strain F113 G22. The second paired comparison was a non-functional modification of wild type (unmarked) strain SBW25, constructed to carry marker genes only, creating strain SBW25 EeZY-6KX. Significant perturbations were found in the indigenous bacterial population structure, with the F113, (DAPG+) strain causing a shift towards slower growing colonies (K strategists) compared with the non-antibiotic producing derivative (F113 G22) and the SBW25 strains. The DAPG+ strain also significantly reduced, in comparison with the other inocula, the total Pseudomonas populations but did not affect the total microbial populations. The survival of F113 and F113 G22 were an order of magnitude lower than the SBW 25 strains. The DAPG+ strain caused a significant decrease in the shoot to root ratio in comparison to the control and other inoculants, indicating plant stress. F113 increased soil alkaline phosphatase, phosphodiesterase and aryl sulphatase activities compared to the other inocula, which themselves reduced the same enzyme activities compared to the control. In contrast to this, the -glucosidase, -galactosidase and N-acetyl glucosaminidase activities decreased with the inoculation of the DAPG+ strain. These results indicate that soil enzymes are sensitive to the impact of GMM inoculation.Peer reviewe

Methods for studying the nematophagous fungus Verticillium chlamydosporium in the root environment

In order to exploit fully the biocontrol potential of the nematophagous fungus Verticillium chlamydosporium, it is important to understand the ecology of the fungus in soil, and interactions with both plant and nematode hosts. Several approaches for studying the fungus in soil and the root environment are compared. These include a semi-selective medium for V. chlamydosporium, PCR primers specific for the fungal beta -tubulin gene, and monoclonal antibodies. In addition to providing a target for species-specific primers, the beta -tubulin gene is implicated in resistance to the fungicides used in the semi-selective medium, and the genetic basis for this is investigated. Culture and PCR-based methods were used to screen for the presence of the fungus in field soils known to have been suppressive to cereal cyst nematode and that contained V. chlamydosporium populations. Monoclonal antibodies specific for either hyphae or conidia of the fungus were obtained, and their application as a tool for visualising the infection process on the root was explored.Peer reviewe