Role of EPS in mitigation of plant abiotic stress: The case of Methylobacterium extorquens PA1

Abstract

Methylobacterium extorquens is a facultative methylotrophic Gram-negative bacterium, often associated with plants, that exhibits a unique ability to grow in the presence of high methanol concentrations, which serves as a single carbon energy source. We found that M. extorquens strain PA1 secretes a mixture of different exopolysaccharides (EPSs) when grown in reference medium or in presence of methanol, that induces the secretion of a peculiar and heterogenous mixture of EPSs, with different structure, composition, repeating units, bulk and a variable degree of methylation. These factors influenced 3D structure and supramolecular assets, diffusion properties and hydrodynamic radius, and likely contribute to increase methanol tolerance and cell stability. No direct methanol involvement in the EPSs solvation shell was detected, indicating that the polymer exposure to methanol is water mediated. The presence of methanol induces no changes in size and shape of the polymer chains, highlighting how water-methanol mixtures are a good solvent for refEPS and metEPS.