Production of exopolysaccharide by Rhizobium leguminosarum bv. trifolii and its role in bacterial attachment and surface properties

Abstract

Background and aims The acidic exopolysaccharide (EPS) produced by Rhizobium leguminosarum bv. trifolii is required for the establishment of effective symbiosis with compatible host plants (Trifolium spp.). In the rhizobium-legume interaction, early stages of root infection and nodule development have been well studied from a genetic standpoint. However, factors important for colonization of several surfaces by rhizobia, including soil particles and roots, have not yet been thoroughly investigated. The aim of this study was establishing of environmental factors affecting production of EPS by R. leguminosarum bv. trifolii strain 24.2 and the role of this polysaccharide in bacterial surface properties and attachment ability. Methods Besides the wild-type strain, its derivatives differing in the level of EPS produced were used to these analyses. The ability of attachment to abiotic and biotic surfaces of these strains were established using CFU counting experiments. Three-dimensional structure and other parameters of biofilms formed were characterized in confocal laser scanning microscopy. Electrokinetic (zeta) potential of rhizobial cells were determined using Laser Doppler Velocimetry. Results It was evidenced that the ability of R. leguminosarum bv. trifolii to produce EPS significantly affected bacterial attachment and biofilm formation on both abiotic and biotic surfaces. In addition, the presence of this polysaccharide influenced the zeta potential of rhizobial cells. Mutant strains having a mutation in genes involved in EPS synthesis were significantly impaired in attachment, whereas strains overproducing this polysaccharide showed higher adhesion efficiency to all of the tested materials. EPS facilitated attachment of bacterial cells to the tested surfaces most probably due to hydrophobic interactions and heterogeneity of the envelope surface. Conclusions EPS produced by R. leguminosarum bv. trifolii plays a significant role in attachment and biofilm formation to both abiotic and biotic surfaces as well as bacterial surface properties.

Extracellular polysaccharide protects Rhizobium leguminosarum cells against zinc stress in vitro and during symbiosis with clover

“…We have previously established that Rt24.2, Rt24.2 (pBA1) and Rt24.2(pBR1) highly effectively adhere to the host roots, whereas the adherence of Rt5819 and Rt2472 is considerably reduced (Janczarek et al, 2015a). In the current study, we examined the effect of Zn 21 ions on the attachment of these strains to clover roots.…”

“…The greatest contribution to this process originates from the symbiosis of soil bacteria, collectively called rhizobia, with legumes (Janczarek et al, 2015b;L opez-Baena et al, 2016). These microorganisms can induce the formation of specific new organs on host plant roots, called nodules, inside of which they fix nitrogen (Oldroyd et al, 2011;Janczarek et al, 2015a).…”

Genetic characterization of the Pss region and the role of PssS in exopolysaccharide production and symbiosis of Rhizobium leguminosarum bv. trifolii with clover

“…Rhizobia secrete large amounts of EPS into the environment (D' Haeze et al 2004;Quelas et al 2006;Janczarek et al 2015a). Although some data concerning genetic characteristics of a few genes involved in EPS synthesis in R. leguminosarum have been published previously, no comprehensive studies on the transcriptional activity of genes grouped in the EPS synthesis region have been performed so far.…”

“…b Ultrastructure of the infection thread: TW -thread wall; TM -thread matrix; BAbacteria; A -amyloplast; bar= 1 μm. c The mature infected plant cell with properly differentiated bacteroids (B); bar=5 μm availability, salinity, pH, and temperature, affect the level of EPS produced by rhizobia (Quelas et al 2006;Skorupska 2009, 2011;Huang et al 2012;Janczarek et al 2015a). The synthesis of EPS is a multi-step process, which involves a coordinated action of many enzymatic proteins.…”

“…ensures adaptation of bacterial cells to changing environmental conditions (Fujishige et al 2006;Flemming and Wingender 2010;Jaszek et al 2014;Janczarek et al 2015a). In the case of soil nitrogen-fixing bacteria, which are able to establish symbiotic interactions with legumes, EPS is also indispensable for effective infection and nodulation of many host plants (e.g., Medicago, Trifolium, Pisum, Vicia spp.)…”