Consolidated bioprocessing of butanol production from xylan by a thermophilic and butanologenic Thermoanaerobacterium sp. M5

Abstract

BackgroundConsolidated bioprocessing (CBP) has attracted increasing attention since it can accomplish hydrolytic enzymes production, lignocellulose degradation and microbial fermentation in one single step. Currently, biobutanol is mainly produced by mesophilic and solventogenic clostridia, such as Clostridium beijerinckii and C. acetobutylicum, which cannot directly utilize lignocellulose, an abundant, renewable and economic feedstock. Hence, metabolic construction or isolation of novel cellulolytic/hemicellulolytic and solventogenic bacteria to achieve direct butanol production from lignocellulose offers a promising alternative.ResultsIn this study, a newly isolated Thermoanaerobacterium sp. M5 could directly produce butanol from xylan through CBP at 55 °C via the butanol–ethanol pathway. Further genomic and proteomic analysis showed that the capabilities of efficient xylan degradation and butanol synthesis were attributed to the efficient expression of xylanase, β-xylosidase and the bifunctional alcohol/aldehyde dehydrogenase (AdhE). Process optimization based on the characteristic of AdhE could further improve the final butanol titer to 1.17 g/L from xylan through CBP. Furthermore, a new co-cultivation system consisting of Thermoanaerobacterium sp. M5 which could release xylose from xylan efficiently and C. acetobutylicum NJ4 which possesses the capacity of high butanol production was established. This microbial co-cultivation system could improve the butanol titer to 8.34 g/L, representing the highest butanol titer from xylan through CBP.ConclusionsA newly thermophilic and butanogenic bacterium Thermoanaerobacterium sp. M5 was isolated and key enzymes responsible for butanol production were characterized in this study. High butanol titer was obtained from xylan through process optimization. In addition, the newly set up microbial co-cultivation system, consisting of Thermoanaerobacterium sp. M5 and C. acetobutylicum NJ4, achieved the highest butanol production from xylan compared with the reported co-cultivation systems.

Consolidated bioprocessing performance of a two‐species microbial consortium for butanol production from lignocellulosic biomass

“…After addition of 1 ml fermented supernatant in 1 ml of reaction mixture, the mixture was incubated at 55°C for 10 min. The detailed method was described by Jiang, Guo et al (2018). Finally, the amount of reducing sugars was calculated by measuring the increasing absorbance at 540 nm according to xylose standard curve.…”

“…Butanol (1.17 g/L) was generated from 30 g/L of hemicellulose after process optimization by using Thermoanaerobacterium sp. strain M5 (Jiang, Guo et al, 2018). However, most cellulolytic strains could not produce butanol owing to the deficiency of key genes responsible for butanol production.…”

Pathway dissection, regulation, engineering and application: lessons learned from biobutanol production by solventogenic clostridia

“…More importantly, with the establishment of co-cultivation system consisting of Thermoanaerobacterium sp. M5 and C. acetobutylicum NJ4, it could effectively enhance the butanol titer to 8.34 g/L from xylan through CBP [127]. However, the CBP technology is still in its infant stage, and microorganisms, microbial consortia and/or condition at industrial scale should be further improved to achieve a high-yield and low-cost CBP process [128,129].…”

Consolidated bioprocessing for butanol production of cellulolytic Clostridia: development and optimization

“…Although several butanol‐producing Clostridia can secrete xylanase and degrade xylan, they lack major lignocellulose‐degrading enzymes (such as endoglucanase, exoglycanase and cellobiohydrolase) (Thomas et al ., ; Jiang et al ., ,b). Basically, Clostridia cannot directly grow on lignocellulose.…”

“…Many commensal consortia have been isolated from nature for butanol production from lignocellulose (Jiang et al ., ,b); however, it remains difficult to regulate these systems due to their complex community structure and the limitation of available genetic tools. Compared with natural consortia, artificial consortia are relatively simple to construct and regulate.…”