Production of Exopolysaccharides by Cultivation of Halotolerant Bacillus atrophaeus BU4 in Glucose-and Xylose-Based Synthetic Media and in Hydrolysates of Quinoa Stalks

Diego Chambi, Jenny Lundqvist, Erik Nygren, Luis Romero-Soto, Katherine Marin, András Gorzsás, Mattias Hedenström, Markus Carlborg, Markus Broström, Ola Sundman, Cristhian Carrasco, Leif J. Jönsson, Carlos Martín

Research output: Contribution to journalArticlepeer-review

Abstract

A halotolerant, exopolysaccharide-producing bacterium isolated from the Salar de Uyuni salt flat in Bolivia was identified as Bacillus atrophaeus using next-generation sequencing. Comparisons indicate that the genome most likely (p-value: 0.0024) belongs to a subspecies previously not represented in the database. The growth of the bacterial strain and its ability to produce exopolysaccharides (EPS) in synthetic media with glucose or xylose as carbon sources, and in hydrolysates of quinoa stalks, was investigated. The strain grew well in all synthetic media, but the growth in glucose was better than that in xylose. Sugar consumption was better when initial concentrations were low. The growth was good in enzymatically produced cellulosic hydrolysates but was inhibited in hemicellulosic hydrolysates produced using hydrothermal pretreatment. The EPS yields were up to 0.064 g/g on initial glucose and 0.047 g/g on initial xylose, and was higher in media with relatively low sugar concentrations. The EPS was isolated and purified by a sequential procedure including centrifugation, cold ethanol precipitation, trichloroacetic acid treatment, dialysis, and freeze-drying. Glucose and mannose were the main sugars identified in hydrolyzed EPS. The EPS was characterized by size-exclusion chromatography, Fouriertransform infrared (FTIR) spectroscopy, heteronuclear single-quantum coherence nuclear magnetic resonance (HSQC NMR) spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. No major differences were elucidated between EPS resulting from cultivations in glucoseor-xylose-based synthetic media, while some divergences with regard to molecular-weight averages and FTIR and HSQC NMR spectra were detected for EPS from hydrolysate-based media.

Original languageEnglish
Article number79
JournalFermentation
Volume8
Issue number2
DOIs
StatePublished - Feb 2022

Bibliographical note

Funding Information:
This research was funded by the Swedish Research Council (2016-05822) and the Bio4Energy research environment (www.bio4energy.se; accessed on 20 December 2021).Stefan Stagge is thanked for support with HPLC and HPAEC. The core facilities and technical platforms at the Chemical Biological Center (KBC) of Umeå University and of the Swedish University of Agricultural Sciences (SLU) are gratefully acknowledged for the provided support. The Biopolymer Analytical Platform supported with the HPSEC. The Vibrational Spectroscopy Core Facility performed the FTIR analysis. The NMR Core Facility provided the HSQC NMR spectra. Umeå Centre for Electron Microscopy and National Microscopy Infrastructure (UCEMNMI) provided the SEM images.

Funding Information:
Funding: This research was funded by the Swedish Research Council (2016-05822) and the Bio4Energy research environment (www.bio4energy.se; accessed on 20 December 2021).

Publisher Copyright:
© 2022 by the author. Licensee MDPI, Basel, Switzerland.

Keywords

  • Bacillus atrophaeus
  • Exopolysaccharide
  • Genome sequencing
  • Halotolerant bacterium
  • Lignocellulose bioconversion
  • Quinoa stalk

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