Exopolysaccharides Production by Cultivating a Bacterial Isolate from the Hypersaline Environment of Salar de Uyuni (Bolivia) in Pretreatment Liquids of Steam-Exploded Quinoa Stalks and Enzymatic Hydrolysates of Curupaú Sawdust

Diego Chambi,Carlos Martín,Roxana Villca,Rajni Hatti-Kaul,Cristhian Carrasco,Jorge Quillaguamán,José Vega-Baudrit,Luis Romero-Soto,Felipe Orozco-Gutiérrez

doi:10.3390/fermentation7010033

Abstract

The halotolerant bacterial strain BU-4, isolated from a hypersaline environment, was identified as an exopolysaccharide (EPS) producer. Pretreatment liquids of steam-exploded quinoa stalks and enzymatic hydrolysates of Curupaú sawdust were evaluated as carbon sources for EPS production with the BU-4 strain, and the produced EPS was characterized using FTIR, TGA, and SEM. Cultivation was performed at 30 °C for 48 h, and the cells were separated from the culture broth by centrifugation. EPS was isolated from the cell pellets by ethanol precipitation, and purified by trichloroacetic acid treatment, followed by centrifugation, dialysis, and freeze-drying. EPS production from quinoa stalks- and Curupaú sawdust-based substrates was 2.73 and 0.89 g L−1, respectively, while 2.34 g L−1 was produced when cultivation was performed on glucose. FTIR analysis of the EPS revealed signals typical for polysaccharides, as well as ester carbonyl groups and sulfate groups. High thermal stability, water retention capacity and gel-forming ability were inferred from SEM and TGA. The capability of the halotolerant isolate for producing EPS from pretreatment liquids and hydrolysates was demonstrated, and characterization of the EPS revealed their broad application potential. The study shows a way for producing value-added products from waste materials using a bacterium from a unique Bolivian ecosystem.

Highlights

It is a Gram-positive bacterium with elongated rod-shaped cells that interact with one another to generate a significant quantity of biofilm as an aggregate
The effect of varying salinity on cell growth and EPS production by BU-4 isolate was screened in a glucose-based medium containing different NaCl amounts
The analysis revealed that glucose represented over 90% of the EPS proin the glucose-based medium, whereaswhereas the EPSthe obtained from thefrom pretreatment liquid of duced in the glucose-based medium, EPS obtained the pretreatment quinoaofstalks wasstalks a heteropolysaccharide with xylosewith and xylose glucoseand accounting for liquid quinoa was a heteropolysaccharide glucose together accounting almost 80%

Summary

Introduction

During the past several decades, a variety of extremophiles, microorganisms isolated from different extreme conditions, such as very high or very low temperatures, low pH, or very high saline concentrations, have been investigated concerning their adaptation to relevant environments, and their biotechnological potential [1,2,3,4]. Halophilic microorganisms belong to a group of extremophiles capable of surviving in salt-rich environments, e.g., saline lakes and soils [5,6,7]. They are distinguished into slight, moderate and extreme halophiles. Slight halophiles, including halotolerant bacteria, do not require NaCl for growth but tolerate salinity levels between 3 and 5% (w/v) NaCl, while moderate and Fermentation 2021, 7, 33.

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