Rhizobia exopolysaccharides: promising biopolymers for use in the formulation of plant inoculants

• Published in: Brazilian journal of microbiology Vol. 53; no. 4; pp. 1843 - 1856
• Main Authors: Palhares Farias, Thiago, de Melo Castro, Elisa, Marucci Pereira Tangerina, Marcelo, Quintino da Rocha, Cláudia, Brito Bezerra, Cicero Wellington, de Souza Moreira, Fatima Maria
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-12-2022; Springer Nature B.V
• Subjects: Bacteria; Biomedical and Life Sciences; Biomolecules; Biopolymers; Biopolymers - metabolism; Biotechnology and Industrial Microbiology - Research Paper; Carbon sources; Cell survival; Chemical composition; Exopolysaccharides; Food Microbiology; Functional groups; Galactose; Infrared spectroscopy; Life Sciences; Magnetic resonance spectroscopy; Mathematical analysis; Medical Microbiology; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Microenvironments; Microorganisms; Mycology; Nitrogen fixation; Nitrogen-fixing bacteria; Nitrogenation; NMR; NMR spectroscopy; Nuclear magnetic resonance; Polymers; Polysaccharides, Bacterial - metabolism; Probiotics; Rhizobium; Rhizobium tropici - metabolism; Scanning electron microscopy; Soil stresses; Spectroscopy, Fourier Transform Infrared; Spectrum analysis; Strains (organisms); Symbiosis; Thermal stability; Water holding; Cellular protection; ,; Bacterial exopolysaccharide; Inoculant carrier; Paraburkholderia, Rhizobium tropici
• ISSN: 1517-8382; 1678-4405
• DOI: 10.1007/s42770-022-00824-z

Inoculants with beneficial microorganisms comprise both selected strains and carriers that ensure a favorable microenvironment for cell survival and stability. Formulations of inoculants using synthetic polymers as carriers are common. However, only a few studies are available in the literature regarding the formulation of inoculants using natural biomolecules as carriers. Exopolysaccharides (EPS) are biomolecules produced by a vast array of microbial species, including symbiotic nitrogen-fixing bacteria, commonly known as rhizobia. EPS perform several functions, such as the protection against the deleterious effects of diverse environmental soil stresses. Two
Rhizobium tropici
strains and one
Paraburkholderia
strain were selected after semiquantitative analysis by scanning electron microscopy (SEM) of their EPS production in liquid YMA medium. Their EPS were characterized through a series of analytical techniques, aiming at their use in the formulation of plant inoculants. In addition, the effect of the carbon source on EPS yield was evaluated. Multi-stage fragmentation analysis showed the presence of xylose, glucose, galactose, galacturonic acid, and glucuronic acid in EPS chemical composition, which was confirmed by FT-IR spectra and
13
C NMR spectroscopy. Thermal stability (thermogravimetric) was close to 270 °C and viscosity ranged from 120 to 1053.3 mPa.s. Surface morphology (SEM) was rough and irregular, with a cross-linked spongy matrix, which, together with the hydrophilic functional groups, confers water holding capacity. The present study showed that the three EPS have potential as microorganism carriers for formulation of microbial inoculants to be applied in plants.