Biomedical subjects

JM Lynch

Publications and source records attributed to JM Lynch.

4 recordsLinked to original sources

PubMed1999

Effects of Pseudomonas fluorescens F113 on Ecological Functions in the Pea Rhizosphere Are Dependent on pH.

> Abstract The aim of this microcosm study was to determine influence of the antibiotic 2,4-diacetylphloroglucinol (DAPG) on the effect of wild-type and functionally modified Pseudomonas fluorescens F113 strains in a sandy loam soil of pH 5.4 planted with pea (Pisum sativum var Montana). The functional modification of strain F113 was a repressed production of DAPG, useful in plant disease control, creating the DAPG negative strain F113 G22; both were marked with a lacZY gene cassette. Lowering the soil pH to 4.4 significantly reduced the plant shoot and root weights and the root length, whereas the bacterial inocula had no significant effect. Both inocula significantly reduced the shoot/root ratio at pH 5.4, but this effect was not evident at the lowered or elevated (6.4) pH levels. The decrease in pH significantly increased the fungal and yeast colony-forming units from the rhizosphere (root extract), but did not affect the total bacterial c.f.u.'s. Inoculatioin with strain F113 in the pH 4.4 soil resulted in a significantly greater total bacterial population. The fungal and yeast c.f.u.'s were not significantly affected by the inocula at any pH studied. Increasing the pH significantly increased the indigenous Pseudomonas population in comparison to the reduced pH treatment and significantly increased both the introduced and total Pseudomonas populations. The antibiotic producing strain significantly reduced the total bacterial population and the NAGase activity (related to fungal activity) at pH 6.4 where the inocula population was the greatest. Alkaline phosphatase, phosphodiesterase, aryl sulfatase, beta-glucosidase, alkaline beta-galactosidase, and NAGase activities significantly increased with increasing in pH. The F113 inocula reduced the acid phosphatase activity at pH 5.4 and increased the acid beta-galactosidase activity over all the pH treatments. The results presented illustrate the variation in impact with soil pH, with implications for variability in efficacy of Pseudomonas fluorescens biocontrol agents with soil pH.http://link.springer-ny.com/link/service/journals/00248/bibs/37n4p248.html

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PubMed1999

Effect of Introduced Pseudomonas fluorescens Strains on Soil Nematode and Protozoan Populations in the Rhizosphere of Wheat and Pea.

Previous studies have shown that inoculation of pea seeds with Pseudomonas fluorescens strains F113lacZY or F113G22 increased mineralization of organic nitrogen in the rhizosphere. In contrast, inoculation of the same strains onto wheat seeds reduced mineralization of N from organic residues incorporated into soil. In the present study, we report on a likely explanation of this phenomenon, which appears to be governed by the effect of plant-microbe interactions on bacterial-feeding nematodes and protozoa. In soil microcosm tests, inoculation of pea seeds with Pseudomonas fluorescens strains F113lacZY or F113G22 resulted in an increase in the number of nematodes and protozoa in the rhizosphere as compared to noninoculated controls. This trend was repeated using a model sand system into which the bacteriophagous nematode Caenorhabditis elegans was introduced. It was subsequently found that non-inoculated germinating pea seeds exerted a nematicidal effect on C. elegans, which was remedied by inoculation with either strain F113lacZY or F113G22. This suggests that nematicidal compounds released by the germinating pea seeds were metabolized by the microbial inoculants before they affected nematode populations in the spermosphere or rhizosphere of pea. In contrast, inoculation of wheat plants resulted in significantly lower nematode populations in the rhizosphere, whereas protozoan numbers were unaffected. No nematicidal effects of inoculated or noninoculated wheat seeds could be found, suggesting that microfaunal populations were affected at a later stage during plant growth. Because of their key roles in accelerating the turnover of microbially immobilized N and organic matter, plants that support a larger microfaunal population are likely to benefit from a higher availability of inorganic nitrogen. Therefore, an understanding of plant-microbe interactions and their effects on soil microfaunal populations is essential in order to assess the effects of microbial inocula on plant mineral nutrition.

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PubMed1998

Effect of Insertion Site and Metabolic Load on the Environmental Fitness of a Genetically Modified Pseudomonas fluorescens Isolate.

An isolate of Pseudomonas fluorescens (SBW25) was modified with different marker genes (lacZY, aph-1, and xylE). These marker genes were inserted singly or in combination into two separate (1 Mbp apart) and presumably nonessential sites (-6- and Ee) on the chromosome of SBW25. This allowed the production of a range of genetically modified SBW25 variants that differed with respect to insertion site of the marker genes and metabolic burden. The environmental fitness of the different SBW25 variants was tested in soil, in the rhizosphere of wheat and pea, and on the phylloplane of wheat. Reduced environmental fitness of the different variants was mainly attributed to the extra metabolic burden of novel gene expression, whereas choice of insertion site was of little significance. Changes in environmental fitness were dependent on the environmental conditions; an environment, such as soil, with a low microbial carrying capacity had a negative effect on the environmental fitness of variants with a large metabolic load. In environments with a larger carrying capacity, such as the rhizosphere of pea, environmental fitness of variants with a large metabolic load was not significantly different from that of variants with a smaller metabolic burden.

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PubMed1998

Terrestrial biotechnology

Ecophysiological and molecular biological investigations of soil microorganisms have developed well, including critical studies of the fate and transport of genetically-modified microorganisms. Such studies will make contributions to areas ranging from the understanding of global change to the catabolism of xenobiotics in soil. Inundative inoculation procedures have not yet sustained their early promise. Greater opportunity appears to lie in the management of indigenous or intrinsic biota. For the protection of human health and the environment, environmental diagnostics, which will include the use of novel biosensors, would seem to offer great prospects.

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