Springer Acta Medica Okayama 16174615 293 4 2018 MexEF-OprN multidrug efflux pump transporter negatively controls N-acyl-homoserine lactone accumulation in pseudomonas syringae pv. Tabaci 6605 1 11 EN Takahiro Sawada Graduate School of Environmental and Life ScienceOkayama University Miho Eguchi Graduate School of Environmental and Life ScienceOkayama University Seiya Asaki Faculty of AgricultureOkayama University Ryota Kashiwagi Faculty of AgricultureOkayama University Kousuke Shimomura Faculty of AgricultureOkayama University Fumiko Taguchi Graduate School of Environmental and Life ScienceOkayama University Hidenori Matsui Graduate School of Environmental and Life ScienceOkayama University Mikihiro Yamamoto Graduate School of Environmental and Life ScienceOkayama University Yoshiteru Noutoshi Graduate School of Environmental and Life ScienceOkayama University Kazuhiro Toyoda Graduate School of Environmental and Life ScienceOkayama University Yuki Ichinose Graduate School of Environmental and Life ScienceOkayama University Our previous studies revealed that flagellar-motility-defective mutants such as ∆fliC of Pseudomonas syringae pv. tabaci 6605 (Pta6605) have remarkably reduced production of N-acyl-homoserine lactones (AHL), quorum-sensing molecules. To investigate the reason of loss of AHL production in ∆fliC mutant, we carried out transposon mutagenesis. Among approximately 14,000 transconjugants, we found 11 AHL production-recovered (APR) strains. In these APR strains, a transposon was inserted into either mexE or mexF, genes encoding for the multidrug efflux pump transporter MexEF-OprN, and mexT, a gene encoding a putative transcriptional activator for mexEF-oprN. These results suggest that MexEF-OprN is a negative regulator of AHL production. To confirm the negative effect of MexEF-OprN on AHL production, loss- and gain-of-function experiments for mexEF-oprN were carried out. The ∆fliC∆mexF and ∆fliC∆mexT double mutant strains recovered AHL production, whereas the mexT overexpressing strain abolished AHL production, although the psyI, a gene encoding AHL synthase, is transcribed as wild type. Introduction of a mexF or mexT mutation into another flagellar-motility- and AHL production-defective mutant strain, ∆motCD, also recovered the ability to produce AHL. Furthermore, introduction of the mexF mutation into other AHL production-defective mutant strains such as ∆gacA and ∆aefR also recovered AHL production but not to the ∆psyI mutant. These results indicate that MexEF-OprN is a decisive negative determinant of AHL production and accumulation. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0944-5013 215 2018 Specific growth inhibitors of Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, X. campestris pv. campestris, and Clavibacter michiganensis subsp. michiganensis 29 35 EN Graduate School of Environmental and Life Science, Okayama University Taku Sawai Graduate School of Environmental and Life Science, Okayama University Yoshiteru Noutoshi Graduate School of Environmental and Life Science, Okayama University Yuta Nishina Research Core for Interdisciplinary Sciences, Okayama University Hidenori Matsui Graduate School of Environmental and Life Science, Okayama University Mikihiro Yamamoto Graduate School of Environmental and Life Science, Okayama University Kazuhiro Toyoda Graduate School of Environmental and Life Science, Okayama University Yuki Ichinose Graduate School of Environmental and Life Science, Okayama University Plant pathogenic bacteria cause huge yield losses in crops globally. Therefore, finding effective bactericides to these pathogens is an immediate challenge. In this study, we sought compounds that specifically inhibit the growth of Ralstonia solanacearum. As a result, we identified one promising compound, 1-(4-bromophenyl)-6-methoxy-2,3,4,9-tetrahydro-1H-β-carboline, which inhibited the growth of R. solanacearum (Rs1002) from a pilot library of 376 chemicals provided from RIKEN. We further obtained its structural analogues and assessed their ability to inhibit Rs1002 growth. Then we identified five compounds, named ralhibitins A to E, that specifically inhibit growth of Rs1002 at >5 μg/ml final concentration. The most effective compounds, ralhibitins A, C, and E completely inhibited the growth of Rs1002 at 1.25 μg/ml. In addition, ralhibitins A to E inhibited growth of Xanthomonas oryzae pv. oryzae but not the other bacteria tested at a final concentration of 10 μg/ml. Whereas, ralhibitin E, besides inhibiting R. solanacearum and X. oryzae pv. oryzae, completely inhibited the growth of X. campestris pv. campestris and the Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis at 10 μg/ml. Growth inhibition by these compounds was stable at pH 6–9 and after autoclaving. Because Rs1002 grew in the culture medium in which ralhibitins were incubated with the ralhibitin-insensitive bacteria, the unaffected bacteria may be able to inactivate the inhibitory effect of ralhibitins. These results suggest that ralhibitins might be potential lead compounds for the specific control of phytopathogenic bacteria. No potential conflict of interest relevant to this article was reported.