Utilizing straw-derived hemicellulosic hydrolysates by Chlorella vulgaris: Contributing to a biorefinery approach

Abstract

With the growing human population, greenhouse gases and global temperature are increasing calling for sustainable biorefineries to convert low-value side streams into high-value products. In this study, the remaining hemicellulosic sugary waste fraction of a wheat straw biorefinery approach, without any pretreatment, was applied as a medium supplement for Chlorella vulgaris cultivation. Next to oligomeric and monomeric sugars, the waste stream contained hydrolysis by-products, such as furfural, 5-hydroxymethylfurfural and acetic acid. Despite the presence of these growth inhibitors, C. vulgaris cultivation was possible. Addition of 2.5% (v/v) of wheat straw hydrolysate to BG11-medium boosted chlorophyll content in C. vulgaris by 40% compared to photoautotrophically grown cells solely cultivated on defined media. As of now, this is the highest chlorophyll content obtained from a cultivation of C. vulgaris on a medium supplemented with a waste stream. Overall, our results demonstrate that wheat straw hydrolysate increases chlorophyll biosynthesis, improving the nutritional value of C. vulgaris biomass for food and feed applications. Hence, valorization of this hemicellulosic sugary fraction results in an additional high-valued product contributing towards the wheat straw biorefinery.

Bioconversion of Furanic Compounds by Chlorella vulgaris—Unveiling Biotechnological Potentials

“…During a previous study, depletion of HMF and FF in Chlorella vulgaris cultivation in hydrolysates obtained from liquid hot water pretreatment [ 22 ] was observed; therefore, further investigation into the conversion of furanic compounds was needed. In order to determine furan metabolism in microalgae, screening experiments were performed photoautotrophically and mixotrophically with the addition of glucose.…”

“…Chlorella vulgaris (UTEX 2714), obtained from the Culture Collection of Algae at the University of Texas at Austin, was used in this study. BG11 [ 22 ] at pH 7.5 was used as the cultivation medium. The inoculum was cultivated at 23 °C, with 3% ( v / v ) CO 2 -enriched air, shaking at 100 rpm in a Minitron shaker (Infors HT, Bottmingen, Switzerland).…”

“…Recently, it was shown that wheat straw hydrolysates from liquid hot water pretreatment composed of monomeric and oligomeric sugars, acetic acid, and furanic compounds can be used for Chlorella vulgaris cultivation [ 22 ]. During those studies, the depletion of furanic compounds in the growth medium was observed.…”

“…Organisms capable of metabolizing 5-Hydroxymethylfurfural (HMF) and furfural (FF), the corresponding resulting metabolites and enzymes responsible for the conversion; R -describes a recombinant enzyme, N -describes a host native enzyme. Recently, it was shown that wheat straw hydrolysates from liquid hot water pretreatment composed of monomeric and oligomeric sugars, acetic acid, and furanic compounds can be used for Chlorella vulgaris cultivation [22]. During those studies, the depletion of furanic compounds in the growth medium was observed.…”