Enhanced bioethanol production from wheat straw hemicellulose by mutant strains of pentose fermenting organisms Pichia stipitis and Candida shehatae.

Sravanthi Koti,Jahnavi Gentela,Sai Prashanthi Govumoni,L Venkateswar Rao

doi:10.1186/s40064-016-3222-1

Abstract

The main aim of the present study was to mutate yeast strains, Pichia stipitis NCIM 3498 and Candida shehatae NCIM 3501 and assess the mutant’s ability to utilize, ferment wheat straw hemicellulose with enhanced ethanol yield. The organisms were subjected to random mutagenesis using physical (ultraviolet radiation) and chemical (ethidium bromide) mutagens. The mutant and wild strains were used to ferment the hemicellulosic hydrolysates of wheat straw obtained by 2 % dilute sulphuric acid and enzymatic hydrolysis by crude xylanase separately. Among all the mutant strains, PSUV9 and CSEB7 showed enhanced ethanol production (12.15 ± 0.57, 9.55 ± 0.47 g/L and yield 0.450 ± 0.009, 0.440 ± 0.001 g/g) as compared to the wild strains (8.28 ± 0.54, 7.92 ± 0.89 g/L and yield 0.380 ± 0.006 and 0.370 ± 0.002 g/g) in both the hydrolysates. The mutant strains were also checked for their consistency in ethanol production and found stable for 19 cycles in hemicellulosic hydrolysates of wheat straw. A novel element in the present study was introduction of chemical mutagenesis in wild type as well as UV induced mutants. This combination of treatments i.e., UV followed by chemical mutagenesis was practically successful.

Highlights

Fossil fuel reserves are limited, and their current oxidation rate is a major global environmental concern with complex and severe climatic impacts (Stephenson et al 2011)
UV and EtBr mutagenesis After separate UV and chemical mutagenesis, combination of UV and chemical mutagenesis was performed and selection of large colonies (42 colonie; from each method 7 colonies) was done on ethanol-containing medium. All these mutants were screened for maximum ethanol production in synthetic fermentation medium
Determination of ethanol produced by all the mutants revealed that only four mutants resulted in significant ethanol productivity in synthetic medium compared to their wild strains

Summary

Introduction

Fossil fuel reserves are limited, and their current oxidation rate is a major global environmental concern with complex and severe climatic impacts (Stephenson et al 2011). The increase in agro-industrial activity has led to the widespread accumulation of large quantities of lignocellulosic residues from wood, forestry, herbaceous, agricultural, solid, and various industrial wastes (José et al 2010). These residues are collectively termed “biomass” and can be converted into ethanol fuel. The production of ethanol from lignocellulosic biomass involves three major processes: pretreatment, hydrolysis, Hemicellulose, a branched polymer composed of pentose and hexose sugars, can be hydrolyzed by hemicellulases or acids to release its monomeric sugars. Xylose and arabinose generally constitute a significant fraction of lignocellulosic biomass; their utilization is essential for a feasible bioethanol production process

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