Seems to regulate the surface properties of the bacterium in the presence of plant cells or plant cell extracts. (1,4-alpha-D-galacturonosyl)n+m + H2O = (1,4-alpha-D-galacturonosyl)n + (1,4-alpha-D-galacturonosyl)m. By certain acidic polysaccharides found in carrot root extract. Belongs to the glycosyl hydrolase 28 family.