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

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, Fourier-transform 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 glucose- or-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.

Production of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate) by <em>Bacillus megaterium</em> LVN01 Using Biogas Digestate

“…These are formed by methanolysis of 3HB, resulting in C4 esters, and 3HV, resulting in C4 and C5 esters (REF). 2-Butenoic, 3-hydroxybutyric, and 2-pentanoic acids are also byproducts of thermal degradation of PHBV [58].…”

Development of Biological Coating from Novel Halophilic Exopolysaccharide Exerting Shelf-Life-Prolonging and Biocontrol Actions for Post-Harvest Applications

“…EPS precipitates were collected by centrifugation at 8000 rpm (at 4 • C) for 20 min. Collected EPS was lyophilized until complete dryness and stored at −20 • C for further use [74].…”

Production and Characterization of Poly(3-hydroxybutyrate) from Halomonas boliviensis LC1 Cultivated in Hydrolysates of Quinoa Stalks

“…The suspension was placed in an orbital incubator (INFORS HT Ecotron, Bottmingen, Switzerland) at 45 • C and 170 rpm for one hour. Then, the enzyme blend Cellic CTec2 (obtained from Sigma-Aldrich, Steinheim, Germany) was added at a load of 200 CMCase units/g biomass, as in previous related research [23], and the mixture was incubated for 72 h under the same conditions. At the end of the saccharification process, the slurry was separated via vacuum filtration.…”

“…Quinoa stalks have a high polysaccharide content that makes them a relevant source of fermentable sugars, which can be released via pretreatment and enzymatic saccharification and used in biorefining [19][20][21]. Pretreatment liquids [22] and enzymatic hydrolysates [23] of quinoa stalks have previously been shown to be suitable for producing biopolymers, namely exopolysaccharides, through cultivation of the halotolerant bacterium Bacillus atrophaeus. It is of high scientific interest to investigate whether quinoa stalk hydrolysates are an appropriate substrate for producing other biopolymers, for instance, PHB, using H. boliviensis.…”