Pathways for methionine biosynthesis in <i>E. coli</i>, <i>P. putida</i> and <i>R. solanacearum</i>.

<p>The MetE and MetH methionine synthases catalyze the methylation of homocysteine to produce methionine, with methyltetrahydrofolate [5-methyl tetrahydropteroyltri-L-glutamate] being the methyl group donor <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036877#pone.0036877-Figge1" target="_blank">[13]</a>.</p

Comparison of the regulation of the methionine biosynthetic pathway in <i>E. coli</i> and <i>R. solanacearum</i>.

<p>Arrows symbolize positive regulation and broken lines negative regulation. The dashed arrow indicates that control of HrpG on <i>metH</i> is only partial.</p

List of strains used in this study.

<p>List of strains used in this study.</p

Expression of <i>metE</i> and <i>metHab</i> is differentially regulated in the presence of plant cells.

<p>Gene expression of <i>metE</i> (A) and <i>metHab</i> (B) was monitored after 16 h of growth in complete medium, minimal medium supplemented with glutamate at 20 mM final concentration, in Gamborg medium containing <i>Arabidopsis thaliana</i> cells, in Gamborg medium without plant cells and in Gamborg medium supplemented with homocysteine at 100 µM final concentration. β-galactosidase activity is expressed in Miller units. Each measurement corresponds to the average of three replicates and bars indicate standard deviations.</p

Expression of <i>metE</i>, <i>metHab</i> and <i>metR</i> in different genetic backgrounds.

<p>Expression of <i>metE</i> (A), <i>metHab</i> (B) and <i>metR</i> (C) was determined after 16 h of growth in minimal medium supplemented with glutamate at a 20 mM final concentration (A and B) and in the presence of plant cells (C). β-galactosidase activity is expressed in Miller units. Each measurement corresponds to the average of three replicates and bars indicate standard deviations.</p

Disease progress curves of the various <i>R. solanacearum</i> methionine mutants on tomato plants.

<p>(A) For each strain 24 plants were inoculated using 50 mL of a bacterial suspension at 10⁷ CFU/mL for each plant. (B) For each strain 12 plants were inoculated by injection of 10⁴ CFU directly into the stem of the plant. Disease progress was rated using a disease index where 0 indicates healthy plants and 4 indicates a 100% wilted plant. For both tests 4 week old tomato plants were used. Results are representative of at least three independent experiments.</p

Determination of the bacterial growth in tomato plants of the different methionine mutants.

<p>For each strain 12 plants were inoculated by injection of 10⁴ CFU directly into the stem of the plant. 4 plants were used to estimate the bacterial density in the plant at 0, 3 and 5 days post-inoculation. Results are expressed in Log of colony number by gram of fresh matter log(cfu/gFW). Bars represent the standard deviation between the averages obtained for four plants from two independent experiments. Stars represent significant difference respectively to the wild type strain according to a Student test (<i>p-</i>value <0,05).</p

A New Class of Quorum Quenching Molecules from <i>Staphylococcus</i> Species Affects Communication and Growth of Gram-Negative Bacteria

<div><p>The knowledge that many pathogens rely on cell-to-cell communication mechanisms known as quorum sensing, opens a new disease control strategy: quorum quenching. Here we report on one of the rare examples where Gram-positive bacteria, the ‘<i>Staphylococcus intermedius</i> group’ of zoonotic pathogens, excrete two compounds in millimolar concentrations that suppress the quorum sensing signaling and inhibit the growth of a broad spectrum of Gram-negative beta- and gamma-proteobacteria. These compounds were isolated from <i>Staphylococcus delphini</i>. They represent a new class of quorum quenchers with the chemical formula <i>N</i>-[2-(<i>1H</i>-indol-3-yl)ethyl]-urea and <i>N</i>-(2-phenethyl)-urea, which we named yayurea A and B, respectively. <i>In vitro</i> studies with the N-acyl homoserine lactone (AHL) responding receptor LuxN of <i>V. harveyi</i> indicated that both compounds caused opposite effects on phosphorylation to those caused by AHL. This explains the quorum quenching activity. Staphylococcal strains producing yayurea A and B clearly benefit from an increased competitiveness in a mixed community.</p></div

Concentration-dependent inhibition of pyocyanin production and growth of <i>P. aeruginosa</i>.

<p><i>P. aeruginosa</i> PAO1 was grown in LB at 30°C with serial dilutions of yayurea A (<b>A</b>), yayurea B (<b>B</b>), furanone (<b>C</b>) and tetracycline (<b>D</b>). Relative pyocyanin production was calculated as the ratio between pyocyanin content and cell density (absorbance at 600 nm). Values represent the means of three independent experiments. Bars indicate standard deviation of the mean, SD.</p

Quenching of QS-regulated pigments and bioluminescence by <i>S. delphini</i>.

<p><i>P. aeruginosa</i> (<b>A</b>), <i>S. marcescens</i> (<b>B</b>), <i>V. harveyi</i> (<b>C</b>) and <i>C. subtsugae</i> (<b>D</b>) were each co-cultivated with <i>S. aureus</i> (1) or <i>S. delphini</i> (2) for 24 h. Pyocyanin, which is excreted by <i>P. aeruginosa</i>, was determined in the supernatant at its absorption maximum A_{520 nm}. Prodigiosin, which is cell wall bound in <i>S. marcescens</i>, was ethanol-extracted from the cell pellet and determined at its absorption maximum A_{534 nm}. Bioluminescence of <i>V. harveyi</i> was intensified by aeration before measuring in a bioluminescence reader. Violacein from <i>C. subtsugae</i> was quantitatively extracted with butanol and determined at its absorption maximum A_{585 nm}.</p