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Category: Bacterial Pathogenesis
Fitness Traits in Soil Bacteria, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817572/9781555813291_Chap32-1.gif /docserver/preview/fulltext/10.1128/9781555817572/9781555813291_Chap32-2.gifAbstract:
One function of soil bacteria is the structuring of the soil under a principle of reciprocity : while bacteria alter the parent rock and stabilize the aggregates (i.e., the basic units of the structure of soils), soil colonization by bacteria is a function of soil structure. In the bulk soil, the free diffusion of water, soluble nutrients and oxygen in the macropores creates other gradients between macropores and micropores. Studying the fitness traits of Pseudomonas fluorescens in soil, Stuart Levy and colleagues demonstrated the importance of the AdnA transcriptional factor in spreading of the bacterium in soil. Although in vivo expression technology (IVET) studies identify large numbers of sequences, assessing the relative importance of each gene requires more traditional genetic studies. An important example of adaptation by horizontal gene transfer (HGT) is the spread of antibiotic resistance genes, and subsequent selection of bacteria harboring those resistance genes. Soil is likely to be a reservoir of a range of antibiotic resistance genes. The environment is a reservoir of pathogenic bacteria which are capable of living free from a host and is likely to harbor many opportunistic pathogens. A good example is Burkholderia cepacia, a species formerly described as a rhizosphere inhabitant and a pathogen of onion, but which has more recently been isolated from patients suffering from cystic fibrosis.
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Biofilm formation by the wild-type (a) and an adnA mutant (b) Pseudomonas fluorescens Pf0-1. Strains possessing a GFP-expressing plasmid were incubated for 24 h in the presence of a glass cover-slip. The cover-slip was gently washed with distilled water, and adherent cells were visualized by fluorescence microscopy at 600x magnification. After 24 h wild-type Pf0-1 has formed a thick, structured biofilm, while disruption of adnA profoundly reduced the ability to initiate growth as a biofilm. The importance of biofilms for soil fitness is suggested by the correlation between the biofilm and soil-persistence defects associated with adnA mutants.
Biofilm formation by the wild-type (a) and an adnA mutant (b) Pseudomonas fluorescens Pf0-1. Strains possessing a GFP-expressing plasmid were incubated for 24 h in the presence of a glass cover-slip. The cover-slip was gently washed with distilled water, and adherent cells were visualized by fluorescence microscopy at 600x magnification. After 24 h wild-type Pf0-1 has formed a thick, structured biofilm, while disruption of adnA profoundly reduced the ability to initiate growth as a biofilm. The importance of biofilms for soil fitness is suggested by the correlation between the biofilm and soil-persistence defects associated with adnA mutants.