Mutants of Lactobacillus plantarum ML11-11 deficient in co-aggregation with yeast exhibited reduced activities of mixed-species biofilm formation.

Lactic acid bacteria (LAB) mutants deficient in inter-species co-aggregation with yeast were spontaneously derived from Lactobacillus plantarum ML11-11, a significant mixed-species biofilm former in static co-cultures with budding yeasts. These non-co-aggregative mutants also showed significant decreases in mixed-species biofilm formation. These results suggest the important role of co-aggregation between LAB and yeast in mixed-species biofilm formation. Cell surface proteins obtained by 5 M LiCl extraction from the wild-type cells and non-co-aggregative mutant cells were analyzed by SDS-PAGE. There was an obvious difference in protein profiles. The protein band at 30 kDa was present abundantly in the wild-type cell surface fraction but was significantly decreased in the mutant cells. This band assuredly corresponded to the LAB surface factors that contribute to co-aggregation with yeasts.

Manganese Ion Increases LAB-yeast Mixed-species Biofilm Formation.

Remarkable LAB-yeast mixed-species biofilm was formed by lactic acid bacteria (LAB) Lactobacillus plantarum ML11-11 isolated from Fukuyama pot vinegar and Saccharomyces cerevisiae. This mixed-species biofilm formation increased in proportion to the YPD medium concentration but decreased in proportion to the MRS medium concentration. The effect of MRS components on mixed-species biofilm formation was investigated in a YPD medium environment, and it was clarified that beef extract (one of the MRS medium components) decreased mixed-species biofilm formation. On the other hand, manganese sulfate (another component in MRS) remarkably increased both LAB single- and LAB-yeast mixed-species biofilm formation. LAB single- and mixed-species biofilm formation were increased in proportion to the manganese sulfate concentration up to 1 mM and 100 µM, respectively. The growth of L. plantarum ML11-11 was increased significantly by the addition of 10 µM manganese sulfate and was resistant to higher concentration of up to 100 mM, but growth of S. cerevisiae was sensitive to manganese ion above 100 µM. These results suggested that mixed-species biofilm formation could be controlled artificially by controlling the manganese ion level.