Bacillus subtilis Early Colonization of Arabidopsis thaliana Roots Involves Multiple Chemotaxis Receptors

ABSTRACT Colonization of plant roots by Bacillus subtilis is mutually beneficial to plants and bacteria. Plants can secrete up to 30% of their fixed carbon via root exudates, thereby feeding the bacteria, and in return the associated B. subtilis bacteria provide the plant with many growth-promoting traits. Formation of a biofilm on the root by matrix-producing B. subtilis is a well-established requirement for long-term colonization. However, we observed that cells start forming a biofilm only several hours after motile cells first settle on the plant. We also found that intact chemotaxis machinery is required for early root colonization by B. subtilis and for plant protection. Arabidopsis thaliana root exudates attract B. subtilis in vitro, an activity mediated by the two characterized chemoreceptors, McpB and McpC, as well as by the orphan receptor TlpC. Nonetheless, bacteria lacking these chemoreceptors are still able to colonize the root, suggesting that other chemoreceptors might also play a role in this process. These observations suggest that A. thaliana actively recruits B. subtilis through root-secreted molecules, and our results stress the important roles of B. subtilis chemoreceptors for efficient colonization of plants in natural environments. These results demonstrate a remarkable strategy adapted by beneficial rhizobacteria to utilize carbon-rich root exudates, which may facilitate rhizobacterial colonization and a mutualistic association with the host

Additional file 1 of Protocol: a simple method for biosensor visualization of bacterial quorum sensing and quorum quenching interaction on Medicago roots

Additional file 1: Figure S1. Spectinomycin resistant bacteria tests of the KYC55 biosensor. Left plate: top row is Rm8530-spec, bottom row is Rm8530-spec with UD1022 ycbU. Right plate: top row is Rm8530-spec, middle row is Rm8530-spec with 100 µg ml-1 YtnP, bottom row is Rm8530-spec with 100 µg ml-1 heat killed YtnP

Additional file 2 of Protocol: a simple method for biosensor visualization of bacterial quorum sensing and quorum quenching interaction on Medicago roots

Additional file 2: Figure S2. Six day after germination (DAG) M. truncatula seedlings do not QQ oxo-C16 AHL. Left plate: top row is Rm8530 alone, bottom row is 10 µM oxo-C16 AHL alone. Right plate: M. truncatula with 10 µM oxo-C16 AHL