Comprehensive investigations of biobutanol production by a non-acetone and 1,3-propanediol generating Clostridium strain from glycerol and polysaccharides.

Fengxue Xin,Wenming Zhang,Min Jiang,Hao Wu,Chao Wang,Weiliang Dong,Jiangfeng Ma

doi:10.1186/s13068-016-0641-8

Abstract

BackgroundLow-cost feedstocks, a single product (butanol), and a high butanol titer are three key points for establishing a sustainable and economically viable process for biological butanol production. Here, we comprehensively investigated the butanol production from mono-substrates, mainly glycerol and polysaccharides, mainly starch and xylan by a newly identified wild-type Clostridium pasteurianum GL11.ResultsStrain GL11 produced 14.7 g/L of butanol with a yield of 0.41 g/g from glycerol in the batch mode without formation of by-products of acetone and 1,3-propanediol (1,3-PDO). With in situ extraction with biodiesel, the amount of butanol was finally improved to 28.8 g/L in the fed-batch mode. Genomic and enzymatic analysis showed that the deficiency of key enzymes involved in acetone and 1,3-PDO pathway within strain GL11 led to the elimination of these by-products, which may also greatly simplify downstream separation. The elimination of acetone and 1,3-PDO and high butanol tolerance contributed to its high butanol production yield from glycerol. More importantly, strain GL11 could directly convert polysaccharides, such as xylan and starch to butanol with secretion of xylanase and amylase via consolidated bioprocessing.ConclusionsThe wild-type strain GL11 was found to be particularly advantageous due to its capability of efficient butanol production from glycerol and polysaccharides with elimination of acetone and 1,3-PDO formation. And the high butanol production with in situ extraction by using biodiesel would significantly enhance the economic feasibility of fermentative production of butanol from glycerol. These unique features of C. pasteurianum GL11 open the door to the possibility of cost-effective biofuels production in large scale.

Highlights

Low-cost feedstocks, a single product, and a high butanol titer are three key points for establishing a sustainable and economically viable process for biological butanol production
Phylogenetic identification, genome sequencing and annotation of C. pasteurianum GL11 When xylan was adopted as the substrate, a colony with relatively high xylanase activity was identified on agar plates after Congo red staining
When strain GL11 was further cultivated in mineral salts medium containing glycerol as the sole carbon source, the main metabolic products detected by GC-flame ionization detector (FID) and HPLC were ethanol, butanol, and VFAs, suggesting that strain GL11 synthesizes butanol via a unique pathway

Summary

Introduction

Low-cost feedstocks, a single product (butanol), and a high butanol titer are three key points for establishing a sustainable and economically viable process for biological butanol production. Butanol production by fermentation of C. pasteurianum from glycerol has been limited by the relatively low butanol titer as compared to those achieved by other sugar-based ABE fermentation processes, such as glucose or molasses. The existence of 1,3-propanediol (1,3-PDO), which is another main product when using glycerol as the substrate, would reduce the overall butanol yield and further increase the subsequent cost of separation [10]. These make the identification of novel bacterial strains for specific applications, such as high butanol production from glycerol with elimination of other products as a promising prospect of future research

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