DIFFUSION OF GLUCOSE IN MICROBIAL EXTRACELLULAR POLYSACCHARIDE AS AFFECTED BY WATER POTENTIAL

Extracellular polysaccharide secretion (EPS) is a salient feature of m any soil bacteria. This study investigates whether an EPS shell modula tes the diffusion rate of nutrients in the immediate microenvironment of soil microorganisms. The diffusion of glucose through pure microbia l polysaccharides xanthan and dextran, and through kaolinite and EPS-a mended kaolinite was measured at several water potentials using a stea dy state method. A specific device was developed to simultaneously mon itor water potential (Psi) using polyethylene glycol (PEG) solutions, and measure diffusion rates. The diffusion rate of glucose increased w ith increasing Psi and volumetric water content in both polysaccharide s. At all Psi values studied, glucose diffused faster in EPS or in EPS -amended clay than in pure clay, due to the higher volumetric water co ntent of EPS and their water-saturated porosity. Water retention and d iffusion characteristics in EPS may thus help soil bacteria to maintai n physiological functions at low water potential. Copyright (C) 1996 E lsevier Science Ltd.