Effect of cell immobilization and pH on Scheffersomyces stipitis growth and fermentation capacity in rich and inhibitory media

Abstract

Background: A wide range of value-added products can potentially be produced by bioprocessing hardwood spent sulfite liquors (HSSLs) that are by-products of pulp and paper industry with a high pentose sugar content. However, besides sugars, HSSLs contain considerable amounts of sulfonated lignin derivatives and acetic acid that inhibit the metabolic activity of most microorganisms. Scheffersomyces stipitis is a yeast with high capacity to ferment the pentose sugar xylose under appropriate microaerophilic conditions but it has limited tolerance to HSSL inhibitors. In the present study, cultivations of suspended and immobilized S. stipitis were compared in terms of growth capacity and by-product formation using rich medium and HSSL to investigate whether the immobilization of cells in calcium alginate beads could be a protection against inhibitors while favoring the presence of microaerophilic conditions. Results: Whereas cell immobilization clearly favored the fermentative metabolism in rich medium, pH control was found to play a more important role than cell immobilization on the ethanol production efficiency from bio-detoxified HSSL (bdHSSL), leading to an improvement of 1.3-fold on the maximum ethanol productivity than using suspended cells. When immobilization and pH control were applied simultaneously, the ethanol yield improved by 1.3-fold with unchanged productivity, reaching 0.26 g ethanol.(g glucose + xylose)

Immobilization of Spathaspora passalidarum NRRL Y-27907 in Calcium Alginate Aiming the Production of Second-Generation Ethanol

“…For free cells (Fig. 3a), it was possible to observe the same behavior reported by Portugal-Nunes et al [39], where Glu increased along with batch fermentations and it was higher than that observed for immobilized cells.…”

“…In the case of the SBF with immobilized cells used in this work (shaker), the oxygen transfer was probable impaired due to the bioreactor and support choice, making it difficult to consume xylose and, consequently, to produce ethanol. Portugal-Nunes et al [39] investigated the effect of S. stipitis immobilization for ethanol production. They reported that the calcium alginate support limited the mass transfer based on the difference in glucose uptake rate between the free and immobilized cells fermentations.…”

Second Generation Bioethanol Production: On the Use of Pulp and Paper Industry Wastes as Feedstock

“…SSLs resulting from pulping of softwood (softwood spent sulfite liquor-SSSL) contain mainly hexoses, while SSLs obtained from pulping of hardwood (hardwood spent sulfite liquor-HSSL) present a higher proportion of pentoses [25]. Furthermore, SSL is a low cost and abundant feedstock with a production estimated in 2015 of 90 billion liters per year [39,113]. SSL also has a high biological oxygen demand, presenting a disposal problem that can be solved by using it for the production of added-value products [114] that include bioethanol, xylitol [115,116], polyhydroxyalkanoates [117,118], organic acids [119], and fumaric acid [120].…”

“…Portugal-Nunes et al (2015) studied the effect of cell immobilization and pH on S. stipitis fermentation of bio-detoxified SSL of E. globulus (hardwood). The simultaneous application of cell immobilization and pH control at 5.5 favored the fermentative metabolism, leading to an improvement of 1.3-fold on the ethanol yield and maintaining the volumetric productivity [113]. Harner et al (2015) used genome shuffling to obtain Pachysolen tannophilus mutants with higher tolerance to inhibitors in HSSL.…”

“…S. stipitis is also highly sensitive to the inhibitors found in HSSLs, such as formic, acetic and levulinic acids, phenolics, and furfural [25]. The techniques that have already studied to alleviate this inhibitory effect can be divided in two groups: one based on the removal of inhibitory compounds using different detoxification methods (e.g., biological [113,135], ion exchange [134,138,149]) and the other based on the increasing the tolerance of microorganisms to the inhibitors (e.g., by UV mutagenesis and genome shuffling [137], by adaptation to the HSSL [113,133]).…”