Regulation by Organic Acids of Microbe - plant Interactions Polysaccharide - mediated

A po)ysaccharide flocculant of Klebsiella pneumoniae H12 has been suggested to mediate microbe-plant interactions with the aid of Ca2' [K. Nakata et al., Biosci. BiotechnoL Biochern., 64, 459-465, 2ooOl. Here, twoway regulation of polysaccharide-mediated i"teractions between KL pneumoniae and Ruphanus sativus was studied using organic acids. Namety, 10 mM equiyatents of organic acids promoted production of the polysaccharide by the bacterium, but inhibited flocculation of bacterial cells by the polysaccharide. These phenomena were counterba]anced by equi-molar equiyalents of Ca2+, suggesting cempetition for Ca2+ between the carboxylic residues ef the polysaccharide and those of the aliphatic acids. By electron microscopy observations, bacterial cell aggregates were sparsely distributed oyer