Characterization of Exopolysaccharides Produced by Rhizobia Species

Tereza Cristina Luque Castellane,Eliana Gertrudes De Macedo Lemos,Alda Maria Machado Bueno Otoboni

doi:10.1590/01000683rbcs20150084

Tereza Cristina Luque Castellane, Eliana Gertrudes De Macedo Lemos + Show 1 more

Open Access

https://doi.org/10.1590/01000683rbcs20150084

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Abstract

ABSTRACT Increasing attention has been given, over the past decades, to the production of exopolysaccharides (EPS) from rhizobia, due to their various biotechnological applications. Overall characterization of biopolymers involves evaluation of their chemical, physical, and biological properties; this evaluation is a key factor in understanding their behavior in different environments, which enables researchers to foresee their potential applications. Our focus was to study the EPS produced by Mesorhizobium huakuii LMG14107, M. loti LMG6125, M. plurifarium LMG11892,Rhizobium giardini bv. giardiniH152T, R. mongolense LMG19141, andSinorhizobium (= Ensifer)kostiense LMG19227 in a RDM medium with glycerol as a carbon source. These biopolymers were isolated and characterized by reversed-phase high-performance liquid chromatography (RP-HPLC), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopies. Maximum exopolysaccharide production was 3.10, 2.72, and 2.50 g L-1for the strains LMG6125, LMG19227, and LMG19141, respectively. The purified EPS revealed prominent functional reactive groups, such as hydroxyl and carboxylic, which correspond to a typical heteropolysaccharide. The EPS are composed primarily of galactose and glucose. Minor components found were rhamnose, glucuronic acid, and galacturonic acid. Indeed, from the results of techniques applied in this study, it can be noted that the EPS are species-specific heteropolysaccharide polymers composed of common sugars that are substituted by non-carbohydrate moieties. In addition, analysis of these results indicates that rhizobial EPS can be classified into five groups based on ester type, as determined from the 13C NMR spectra. Knowledge of the EPS composition now facilitates further investigations relating polysaccharide structure and dynamics to rheological properties.

Highlights

Soil bacteria collectively termed rhizobia are taxonomically, metabolically, and genetically diverse (Marcondes et al, 2014)
The strains used throughout this study Mesorhizobium huakuii LMG14107, Mesorhizobium loti LMG6125, Mesorhizobium plurifarium LMG11892, Rhizobium mongolense LMG19141, and Sinorhizobium (= Ensifer) kostiense LMG19227 - were obtained from the collection of the Laboratorium voor Microbiologie, Universiteit Gent, Belgium
For comparative analyses of EPS production obtained from the rhizobial strains, the monosaccharide compositions, and the Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) analyses of the EPS of the strains, pre-inoculum and batch experiments were performed using Rhizobium defined medium (RDM) (0.23 g L-1 K2HPO4, 0.1 g L-1 MgSO4, and 1.1 g L-1 C5H8NaO4.H2O, 4 mL L-1 glycerol, pH 6.8) (Bishop et al, 1976)

Summary

Introduction

Soil bacteria collectively termed rhizobia are taxonomically, metabolically, and genetically diverse (Marcondes et al, 2014). Most bacteria known as legume symbionts belong to the genera of the α- Proteobacteria class, listed as Rhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium, and Ensifer (formerly Sinorhizobium) (Berrada and Fikri-Benbrahim, 2014; Carareto et al, 2014; Marcondes et al, 2014). Interest in the exploitation of microorganisms for production of valuable polysaccharides has greatly increased in recent years, since these biopolymers produced by a variety of microorganisms are chemically well defined and have attracted worldwide attention due to their novel and unique physical properties as bioadhesives, bioflocculants, biosorbents, gelling agents, probiotics, stabilizers, and thickeners, making them suitable for numerous commercial applications in the bionanotechnology, food, pharmaceutical, cosmetics, petroleum, civil construction, and environmental sectors They have the advantages of being ecofriendly, non-toxic, and biodegradable (Freitas et al, 2011; Donot et al, 2012)

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