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Strain competition and agar affect the interaction of rhizobia with rice

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Competition assays with Sinorhizobium meliloti 1021 and its GFP-labelled pSymA cured and deleted derivatives, SmA818 and SmA146, demonstrated that Sm1021 could still inhibit rice seedling growth even when outnumbered by a large excess of the noninhibitory cured or deleted strain. The wild-type strain Sm1021 also inhibited the growth of its noninhibitory pSymA-cured strain SmA818(gfp) and its pSymA-deleted strain SmA146(gfp) in a manner suggesting that Sm1021 produced a bacteriocin-like substance. The production of, and resistance to, this substance seemed to be pSymA-associated, but it was not the cause of killing in competition experiments on rice, suggesting that the killing of SmA818(gfp) and SmA146(gfp) was medium dependent. The addition of agar in liquid F10 medium at concentrations ≤0.4% (m/v) abolished the rice growth inhibition of strain Sm1021 and Sm1021(gfp). The increased medium viscosity at higher agar concentrations decreased the diffusion of gases and small molecules through the media. Thus, the low agar concentrations may mimic waterlogged soil conditions leading to the production of inhibitory compounds by the bacterial strains under microaerobic conditions.

Des tests de compétition réalisés avec Sinorhizobium meliloti 1021 et ses dérivés SmA818 et SmA146 marqués à la GFP, respectivement curé du plasmide pSymA et dont le plasmide a été supprimé, ont demontre que Sm1021 peut encore inhiber la croissance de plantules de riz même s’il est surpassé en nombre par un grand excès de cellules non inhibitrices des souches curées ou déficientes. La souche sauvage Sm1021 inhibe aussi la croissance de la souche non inhibitrice, curée du plasmide pSymA SmA818(gfp) et de la souche déficiente en pSymA SmA146(gfp) d’une manière suggérant que Sm1021 produit une substance de type bactériocine. La production et la résistance à cette substance semble est abalit associées à pSymA, mais ce dernier n’est pas responsable de la mort lors d’expériences de compétition sur le riz, ce qui suggère que la mort de SmA818(gfp) et de SmA146(gfp) était dépendante du milieu. L’ajout d’agar dans le milieu F10 à des concentrations inferieures ou égales à 0.4 % (p/v) abolissait l’inhibition de la croissance du riz par les souches Sm1021 et Sm1021(gfp). L’augmentation de la viscosité du milieu à de plus fortes concentrations d’agar peut avoir diminué la diffusion des gaz et des petites molécules à travers le milieu. Ainsi, de faibles concentrations d’agar peuvent mimer des conditions de sol détrempé, permettant la production de composés inhibiteurs par les souches bactériennes en conditions micro-aérobies.

Document Type: Research Article

Publication date: October 1, 2009

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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