NAHSL-breakdown and biocontrol activity of the<i>R.erythropolis qsdA</i> deletion mutant in potato tubers.

<p>(A) The <i>R. erythropolis</i> R138 wild-type (BCA) and the <i>R. erythropolis</i> R138 Δ<i>qsdA</i> (BCA-Δ<i>qsdA</i>) strains were compared for biocontrol activity against <i>P. atrosepticum</i> 6276 (<i>Pa</i>-QS+) 1, 2, 3 and 7 days after inoculation of potato tubers. For the controls, one or both strains were replaced in the inoculum with a 0.9% NaCl solution. Significant differences (Mann and Whitney test; <i>α</i> = 0.05) in maceration symptoms between infected tubers inoculated with the BCA or the BCA-Δ<i>qsdA</i> are indicated with an asterisk. (B) Population dynamics of <i>P. atrosepticum</i> and <i>R. erythropolis</i> bacteria (CFU/g fresh weight of potato tubers; black and red lines respectively), and NAHSL concentrations (ng/g of potato tubers; black and white bars) were determined for each condition in potato tubers. For lines and bars, each value is the mean of three replicates with the standard deviation indicated. NS, non-significant; NAHSL, <i>N</i>-acyl homoserine lactone.</p

Bacterial strains and plasmids.

<p>Km^R, Ap^R, Gm^R and Tc^R indicate resistance to kanamycin, ampicillin, gentamicin and tetracycline, respectively. NAHSL, <i>N</i>-acyl homoserine lactone; CFBP, Collection Française de Bactéries associées aux Plantes, Institut National de la Recherche Agronomique (INRA), Angers, France.</p

Induction of<i>qsdA</i> gene transcription, NAHSL-breakdown and biocontrol activity of <b><i>R. erythropolis</i></b> in potato tubers.

<p>(A) <i>qsdA</i> gene transcription and biocontrol activity of the <i>R. erythropolis</i> BCA-<i>qsdA::gfp</i> against <i>P. atrosepticum</i> 6276 defective (<i>Pa</i>-QS<b>–</b>) or not (<i>Pa</i>-QS<b>+</b>) for NAHSL production were analyzed at 1, 2, 3 and 7 days after inoculation of <i>S. tuberosum</i> var. Allians tubers. For the controls, one of the two strains was replaced in the inoculum with a 0.9% NaCl solution. Asterisks indicate significantly less severe maceration symptoms in the presence of the BCA-<i>qsdA::gfp</i>, as assessed with the Mann and Whitney test (<i>α</i> = 0.05). The fluorescence of the BCA-<i>qsdA::gfp</i> was analyzed by confocal laser scanning microscopy. (B) The numbers of <i>P. atrosepticum</i> (black lines) and <i>R. erythropolis</i> (red lines) bacteria per unit weight (CFU/g fresh weight of potato tubers), and NAHSL concentration (ng/g of potato tubers; black and white bars) were determined for each condition in potato tubers. For lines and bars, each value is the mean of three replicates with the standard deviation indicated. NS, non-significant; NAHSL, <i>N</i>-acyl homoserine lactone.</p

NAHSL-breakdown and biocontrol activity of the QsdA-expressing<i>E. coli</i> strain in potato tubers.

<p>(A) <i>E. coli</i> DH5α(pUC19) (<i>Ec</i>) and <i>E. coli</i> DH5α(pUC19-<i>qsdA</i>) (<i>Ec-qsdA</i>) were compared for biocontrol activity against <i>P. atrosepticum</i> 6276 (<i>Pa</i>-QS+) 1, 2, 3 and 7 days after inoculation of potato tubers. For the controls, one or both strains were replaced in the inoculum with a 0.9% NaCl solution. Significant differences (Mann and Whitney test; <i>α</i> = 0.05) in maceration symptoms between infected tubers inoculated with the <i>Ec</i> or the <i>Ec-qsdA</i> strains are indicated with an asterisk. (B) Population dynamics of <i>P. atrosepticum</i> and <i>E. coli</i> bacteria (CFU/g fresh weight of potato tubers; black and blue lines respectively), and NAHSL concentration (ng/g of potato tubers; black and white bars), were determined for each condition in potato tubers. For lines and bars, each value is the mean of three replicates with the standard deviation indicated. NS, non-significant; NAHSL, <i>N</i>-acyl homoserine lactone.</p