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Using local residues as raw materials for biorefineries is important for sustainable development. Quinoa stalks can be considered raw materials of choice for local biorefinery initiatives in Bolivia. This investigation aims at proposing a biorefinery process to be applied to quinoa residues using our know-how on lignocellulose bioconversion and the asset of robust microbes isolated from extreme environments. The proposed process consists in treating quinoa stalks in a sequence including extraction of saponins, acid hydrolysis of hemicelluloses and enzymatic saccharification of cellulose for producing hydrolysates to be used in bioconversion processes with different alternative microbes. Saponins are extracted with aqueous ethanol, the saponins-free material is subjected to sulfuricacid-catalyzed hydrothermal pretreatment for separating a stream of hemicellulosic sugars and a cellulignin stream that is then saccharified with commercial cellulases. The extracted saponins can further be processed to value-added products or can be used in the enzymatic saccharification stage for enhancing cellulose conversion. The produced hydrolysates are suitable substrates for producing bacterial biopolymers or ethanol. Residual lignin from the enzymatic saccharification can be upgraded for value-added applications. The results of this investigation show the potential of biorefining of quinoa residues for producing biopolymers using halotolerant bacteria isolated in Bolivian Altiplano.

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.