Novel biobutanol fermentation at a large extractant volume ratio using immobilized Clostridium saccharoperbutylacetonicum N1-4

Metabolically engineer Clostridium saccharoperbutylacetonicum for comprehensive conversion of acid whey into valuable biofuels and biochemicals

As a byproduct of dairy production, the disposal of acid whey poses severe environmental challenges. Herein, an innovative solution involving metabolically engineering Clostridium saccharoperbutylacetonicum to convert all carbon sources in acid whey into sustainable biofuels and biochemicals was presented. By introducing several heterologous metabolic pathways relating to metabolisms of lactose, galactose, and lactate, the ultimately optimized strain, LM-09, exhibited exceptional performance by producing 15.1 g/L butanol with a yield of 0.33 g/g and a selectivity of 89.9%. Through further overexpression of alcohol acyl transferase, 2.7 g/L butyl acetate along with 6.4 g/L butanol was generated, resulting in a combined yield of 0.37 g/g. This study achieves the highest reported butanol titer and yield using acid whey as substrate in clostridia and marks pioneering production of esters using acid whey. The findings demonstrate an innovative bioprocess that enhances renewable feedstock biotransformation, thereby promoting economic viability and environmental sustainability of biomanufacturing.

Two-Phase Fermentation Systems for Microbial Production of Plant-Derived Terpenes

Microbial cell factories, renowned for their economic and environmental benefits, have emerged as a key trend in academic and industrial areas, particularly in the fermentation of natural compounds. Among these, plant-derived terpenes stand out as a significant class of bioactive natural products. The large-scale production of such terpenes, exemplified by artemisinic acid-a crucial precursor to artemisinin-is now feasible through microbial cell factories. In the fermentation of terpenes, two-phase fermentation technology has been widely applied due to its unique advantages. It facilitates in situ product extraction or adsorption, effectively mitigating the detrimental impact of product accumulation on microbial cells, thereby significantly bolstering the efficiency of microbial production of plant-derived terpenes. This paper reviews the latest developments in two-phase fermentation system applications, focusing on microbial fermentation of plant-derived terpenes. It also discusses the mechanisms influencing microbial biosynthesis of terpenes. Moreover, we introduce some new two-phase fermentation techniques, currently unexplored in terpene fermentation, with the aim of providing more thoughts and explorations on the future applications of two-phase fermentation technology. Lastly, we discuss several challenges in the industrial application of two-phase fermentation systems, especially in downstream processing.

Clostridium sp. as Bio-Catalyst for Fuels and Chemicals Production in a Biorefinery Context

Clostridium sp. is a genus of anaerobic bacteria capable of metabolizing several substrates (monoglycerides, diglycerides, glycerol, carbon monoxide, cellulose, and more), into valuable products. Biofuels, such as ethanol and butanol, and several chemicals, such as acetone, 1,3-propanediol, and butyric acid, can be produced by these organisms through fermentation processes. Among the most well-known species, Clostridium carboxidivorans, C. ragsdalei, and C. ljungdahlii can be highlighted for their ability to use gaseous feedstocks (as syngas), obtained from the gasification or pyrolysis of waste material, to produce ethanol and butanol. C. beijerinckii is an important species for the production of isopropanol and butanol, with the advantage of using hydrolysate lignocellulosic material, which is produced in large amounts by first-generation ethanol industries. High yields of 1,3 propanediol by C. butyricum are reported with the use of another by-product from fuel industries, glycerol. In this context, several Clostridium wild species are good candidates to be used as biocatalysts in biochemical or hybrid processes. In this review, literature data showing the technical viability of these processes are presented, evidencing the opportunity to investigate them in a biorefinery context.

Using poly(vinyldodecylimidazolium bromide) for the in-situ product recovery of n-butanol

The mitigation of end-product inhibition during the biosynthesis of n-butanol is demonstrated for an in-situ product recovery (ISPR) system employing a poly(ionic liquid) (PIL) absorbent. The thermodynamic affinity of poly(vinyldodecylimidazolium bromide) [P(VC₁₂ ImBr)] for n-butanol, acetone and ethanol versus water was measured at conditions experienced in a typical acetone-ethanol-butanol (ABE) fermentation. In addition to providing a high n-butanol partition coefficient (PC = 6.5) and selectivity (α_BuOH/water = 46), P(VC₁₂ ImBr) is shown to be biocompatible with Saccharomyces cerevisiae and Clostridium acetobutylicum. Furthermore, the diffusivity of n-butanol in a hydrated PIL provides absorption rates that support ISPR applications. Using a 5 wt% PIL phase fraction relative to the aqueous phase mass, P(VC₁₂ ImBr) improved the volumetric productivity of a batch ABE ISPR process by 31% relative to a control fermentation. The concentration of n-butanol in the P(VC₁₂ ImBr) phase was sufficient to increase the alcohol concentration from 1.5 wt% in the fermentation medium to 25 wt% in the saturated PIL, thereby facilitating downstream n-butanol recovery.

Semi-hydrolysate of paper pulp without pretreatment enables a consolidated fermentation system with in situ product recovery for the production of butanol

Utilization of lignocellulosic biomasses for biobutanol fermentation usually requires costly processes of pretreatment and enzymatic hydrolysis. In this study, paper pulp (93.2% glucan) was used as a starting biomass material to produce biobutanol. We conducted enzymatic semi-hydrolysis of paper pulp without pretreatment and with low enzyme loading, which produced high concentrations of cellobiose (13.9 g L^-1) and glucose (21.3 g L^-1). In addition, efficient fermentation of the semi-hydrolysate was achieved similar to that with the use of commercial sugars without inhibitors. Finally, we designed a novel non-isothermal simultaneous saccharification and fermentation with in situ butanol recovery, which was composed of a repeated semi-hydrolysis process and successive butanol-extractive fermentation process under the respective optimal conditions. The consolidated system improved butanol production, butanol yields, and butanol productivities and enabled repeated use of medium when compared with other integrated hydrolysis and fermentation processes.