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Summary: Chemotaxis and substrate-regulated motility of the rice isolate Xanthobacter sp. JW-KR2 was studied. Growth on alcohols produced motile cells possessing several peritrichous flagella while growth in the presence of organic acids, such as succinate, repressed flagellar synthesis, leading to nonmotile cells. Addition of 2.5 mM-adenosine 3”,5′-cyclic monophosphate (cAMP) to the culture resulted in motile cells even when succinate was the sole carbon source. Chemotaxis assays using microcapillary pipettes revealed a positive response to 1-propanol, 2-propanol, 1-butanol, 2-butanol and 1-pentanol but not to methanol, ethanol, isoamyl alcohol, hexanol, sugars, Casamino acids, tricarboxylic acid (TCA) cycle intermediates, butyrate, propionate, acetone or rice root exudates. The presence of TCA cycle intermediates in the chemotaxis assay inhibited chemotaxis towards butanol. Although the direct role of mobility and chemotaxis in the Xanthobacter–rice interaction is uncertain, one possibility is that Xanthobacter uses alcohols as a signal to move towards microaerobic zones, such as the rice rhizosphere, where carbon and energy sources such as H2, CO2, organic acids, alcohols and other anaerobic metabolites are present. |
