| Summary: | Previously, we reported that the coculture of motile <i>Methylobacterium</i> sp. ME121 and non-motile <i>Kaistia</i> sp. 32K, isolated from the same soil sample, displayed accelerated motility of strain ME121 due to an extracellular polysaccharide (EPS) produced by strain 32K. Since EPS is a major component of biofilms, we aimed to investigate the biofilm formation in cocultures of the two strains. The extent of biofilm formation was measured by a microtiter dish assay with the dye crystal violet. A significant increase in the amount of biofilm was observed in the coculture of the two strains, as compared to that of the monocultures, which could be due to a metabolite produced by strain 32K. However, in the coculture with strain 32K, using <i>Escherichia coli</i> or <i>Pseudomonas aeruginosa</i>, there was no difference in the amount of biofilm formation as compared with the monoculture. Elevated biofilm formation was also observed in the coculture of strain ME121 with <i>Kaistia adipata</i>, which was isolated from a different soil sample. <i>Methylobacterium radiotolerans</i>, isolated from another soil sample, showed a significant increase in biofilm formation when cocultured with <i>K. adipata</i>, but not with strain 32K. We also found that the culture supernatants of strains 32K and <i>K. adipata</i> accelerated the motility of strains ME121 and <i>M. radiotolerans</i>, wherein culture supernatant of <i>K. adipata</i> significantly increased the motility of <i>M. radiotolerans</i>, as compared to that by the culture supernatant of strain 32K. These results indicated that there was a positive relationship between accelerated motility and increased biofilm formation in <i>Methylobacterium</i> spp. This is the first study to report that the metabolites from <i>Kaistia</i> spp. could specifically modulate the biofilm-forming ability of <i>Methylobacterium</i> spp. <i>Methylobacterium</i> spp. biofilms are capable of inhibiting the biofilm formation of mycobacteria, which are opportunistic pathogens that cause problems in infectious diseases. Thus, the metabolites from the culture supernatant of <i>Kaistia</i> spp. have the potential to contribute to the environment in which increased biofilm production of Methylobacterium is desired.
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