Ethanol production from alkali-treated rice straw via simultaneous saccharification and fermentation using newly isolated thermotolerant Pichia kudriavzevii HOP-1

Abstract

In this study, simultaneous saccharification and fermentation (SSF) was employed to produce ethanol from 1% sodium hydroxide-treated rice straw in a thermostatically controlled glass reactor using 20 FPU gds⁻¹ cellulase, 50 IU gds⁻¹ β-glucosidase, 15 IU gds⁻¹ pectinase and a newly isolated thermotolerant Pichia kudriavzevii HOP-1 strain. Scanning electron micrograph images showed that the size of the P. kudriavzevii cells ranged from 2.48 to 6.93 μm in diameter while the shape of the cells varied from oval, ellipsoidal to elongate. Pichia kudriavzevii cells showed extensive pseudohyphae formation after 5 days of growth and could assimilate sugars like glucose, sucrose, galactose, fructose, and mannose but the cells could not assimilate xylose, arabinose, cellobiose, raffinose, or trehalose. In addition, the yeast cells could tolerate up to 40% glucose and 5% NaCl concentrations but their growth was inhibited at 1% acetic acid and 0.01% cyclohexamide concentrations. Pichia kudriavzevii produced about 35 and 200% more ethanol than the conventional Saccharomyces cerevisiae cells at 40 and 45°C, respectively. About 94% glucan in alkali-treated rice straw was converted to glucose through enzymatic hydrolysis within 36 h. Ethanol concentration of 24.25 g l⁻¹ corresponding to 82% theoretical yield on glucan basis and ethanol productivity of 1.10 g l⁻¹ h⁻¹ achieved using P. kudriavzevii during SSF hold promise for scale-up studies. An insignificant amount of glycerol and no xylitol was produced during SSF. To the best of our knowledge, this is the first study reporting ethanol production from any lignocellulosic biomass using P. kudriavzevii.

Preliminary Analysis of Sugar Supplementation on Alcoholic Fermentation by <i>Meyerozyma guilliermondii</i>

“…In this study, both M. guilliermondii and S. cerevisiae exhibited a low degree of flexibility towards the conversion of galactose to ethanol (figure 4B). The weak assimilation of galactose tallies with reports that suggest most yeast species are not fully adaptable towards galactose metabolism [21], [38]. This observation could be attributed to several factors including but not limited to its proton transport assembly and slow substrate affinities of its metabolic enzymes which could eventually cause feedback inhibition, thus decreasing the output.…”

“…Some of these unique non Saccharomyces yeasts include Zygosaccharomyces rouxii [14], [16], [17], [18]. Kluyveromyces marxianus [19], [20], Pichia kudriavzevii [21], [22], Dekkera bruxellensis [23], Zygosaccharomyces bailii [24]. Meyerozyma guilliermondii, a telemorph of Candida guilliermondii or wine yeast is one of such promising non Saccharomyces yeasts obtained from environmental samples with unique biotechnological applications and biological control potential [25], [26], [27], [28].…”

Isolation and characterization of yeasts capable of efficient utilization of hemicellulosic hydrolyzate as the carbon source

“…This type of yeast was isolated from various sources, such as cotton stalks and straw (containing lignocellulosic hydrolyzates), subjected to different treatments, including enzymatic hydrolysis with cellulases. This strain showed better ethanol production (up to 200%) under conditions of high temperature, compared to S. cerevisiae (Dhaliwal et al, 2011;Isono et al, 2011;Kaur et al, 2011;Oberoi et al, 2012). Fonseca (2009) have reported to use of a strain of I. orientalis to reduce the toxic components of hemicellulosic hydrolyzates.…”

Synthetic Biology and Metabolic Engineering Approaches and Its Impact on Non-Conventional Yeast and Biofuel Production

“…D. bruxellensis and S. cerevisiae possesses an almost similar molecular mechanism for this trait (Piskur et al, 2006). Kwon et al (2011) reported that P. kudriavzevii is extremely tolerant to 3 g/L furfural and also tolerate acetic acid of up to 10 g/L (Oberoi et al, 2012) and formic acid up to 2 g/L (Dandi et al, 2013). The genetic engineering tools for this yeast are limited, and genome sequence has recently been reported by Chan et al (2012).…”