Catalytic upgrading of butyric acid towards fine chemicals and biofuels

Butyric Acid Production by Fermentation: Employing Potential of the Novel Clostridium tyrobutyricum Strain NRRL 67062

In this study, the ability of a novel strain of Clostridium tyrobutyricum NRRL 67062 to produce butyric acid during glucose fermentation was evaluated. The strain was evaluated for substrate and product inhibition in batch experiments using anaerobic tubes. To characterize glucose inhibition, initial glucose concentrations ranging from 60 to 250 g L−1 were used, and it was demonstrated that a glucose concentration of 250 g L−1 exerted strong inhibition on cell growth and fermentation. To evaluate butyric acid inhibition, the culture was challenged with 5–50 g L−1 of butyric acid at an initial pH of 6.5. These experiments were performed without pH control. When challenged with a butyric acid concentration of 50 g L−1, cell growth was slow; however, it produced 8.25 g L−1 of butyric acid. This suggested that the butyric acid tolerance of the culture was 58 g L−1. In a scaled-up batch experiment, which was performed in a 2.5 L fermentor with an initial glucose concentration of 100 g L−1, the pH was controlled at 6.5. In this experiment, the strain produced 57.86 g L−1 of butyric acid and 12.88 g L−1 of acetic acid, thus producing 70.74 g L−1 of total acids with a productivity of 0.69 g·L−1·h−1. A concentration of 70.74 g L−1 of acids equates to a yield of 0.71 g of acid per g consumed glucose. The maximum cell concentration was 3.80 g L−1, which may have been the reason for high productivity in the batch culture. Finally, corn steep liquor (CSL; a commercial nutrient solution) provided greater growth and acid production than the refined medium.

Biohydrogen production by mixed culture of Megasphaera elsdenii with lactic acid bacteria as Lactate-driven dark fermentation

Numerous attempts have been made to upscale biohydrogen production via dark fermentation (DF); however, the Achilles' heel of DF, i.e., lactic acid bacteria (LAB) contamination and overgrowth, hinders such upscaling. Key microbes are needed to develop a lactate-driven DF system that can serve as a lactate fermentation platform. In this study, the utility of Megasphaera elsdenii and LAB co-culturing in lactate-driven DF was evaluated. When inoculated simultaneously with LAB or after LAB culture, M. elsdenii achieved a stable hydrogen yield of 0.95-1.49 H₂-mol/mol-glucose, approximately half that obtained in pure M. elsdenii cultures. Hydrogen production was maintained even at an initial M. elsdenii-to-LAB cell ratio of one-millionth or less. Moreover, M. elsdenii produced hydrogen via lactate-driven DF from unusable sugars such as xylose or cellobiose. Thus, M. elsdenii could be a Game changer instrumental in unlocking the full potential of DF.

Production of Propene from n-Butanol: A Three-Step Cascade Utilizing the Cytochrome P450 Fatty Acid Decarboxylase OleTJE

Propene is one of the most important starting materials in the chemical industry. Herein, we report an enzymatic cascade reaction for the biocatalytic production of propene starting from n-butanol, thus offering a biobased production from glucose. In order to create an efficient system, we faced the issue of an optimal cofactor supply for the fatty acid decarboxylase OleTJE , which is said to be driven by either NAD(P)H or H2 O2 . In the first system, we used an alcohol and aldehyde dehydrogenase coupled to OleTJE by the electron-transfer complex putidaredoxin reductase/putidaredoxin, allowing regeneration of the NAD+ cofactor. With the second system, we intended full oxidation of n-butanol to butyric acid, generating one equivalent of H2 O2 that can be used for the oxidative decarboxylation. As the optimal substrate is a long-chain fatty acid, we also tried to create an improved variant for the decarboxylation of butyric acid by using rational protein design. Within a mutational study with 57 designed mutants, we generated the mutant OleTV292I , which showed a 2.4-fold improvement in propene production in our H2 O2 -driven cascade system and reached total turnover numbers >1000.

Recent advances in n-butanol and butyrate production using engineered Clostridium tyrobutyricum

Acidogenic clostridia naturally producing acetic and butyric acids has attracted high interest as a novel host for butyrate and n-butanol production. Among them, Clostridium tyrobutyricum is a hyper butyrate-producing bacterium, which re-assimilates acetate for butyrate biosynthesis by butyryl-CoA/acetate CoA transferase (CoAT), rather than the phosphotransbutyrylase-butyrate kinase (PTB-BK) pathway widely found in clostridia and other microbial species. To date, C. tyrobutyricum has been engineered to overexpress a heterologous alcohol/aldehyde dehydrogenase, which converts butyryl-CoA to n-butanol. Compared to conventional solventogenic clostridia, which produce acetone, ethanol, and butanol in a biphasic fermentation process, the engineered C. tyrobutyricum with a high metabolic flux toward butyryl-CoA produced n-butanol at a high yield of > 0.30 g/g and titer of > 20 g/L in glucose fermentation. With no acetone production and a high C4/C2 ratio, butanol was the only major fermentation product by the recombinant C. tyrobutyricum, allowing simplified downstream processing for product purification. In this review, novel metabolic engineering strategies to improve n-butanol and butyrate production by C. tyrobutyricum from various substrates, including glucose, xylose, galactose, sucrose, and cellulosic hydrolysates containing the mixture of glucose and xylose, are discussed. Compared to other recombinant hosts such as Clostridium acetobutylicum and Escherichia coli, the engineered C. tyrobutyricum strains with higher butyrate and butanol titers, yields and productivities are the most promising hosts for potential industrial applications.

Biodiesel and flavor compound production using a novel promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from the psychrophilic bacterium Halocynthiibacter arcticus

BACKGROUND

Biodiesel and flavor compound production using enzymatic transesterification by microbial lipases provides mild reaction conditions and low energy cost compared to the chemical process. SGNH-type lipases are very effective catalysts for enzymatic transesterification due to their high reaction rate, great stability, relatively small size for convenient genetic manipulations, and ease of immobilization. Hence, it is highly important to identify novel SGNH-type lipases with high catalytic efficiencies and good stabilities.

RESULTS

A promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from Halocynthiibacter arcticus was catalytically characterized and functionally explored. HaSGNH1 displayed broad substrate specificity that included tert-butyl acetate, glucose pentaacetate, and p-nitrophenyl esters with excellent stability and high efficiency. Important amino acids (N83, M86, R87, F131, and I173F) around the substrate-binding pocket were shown to be responsible for catalytic activity, substrate specificity, and reaction kinetics. Moreover, immobilized HaSGNH1 was used to produce high yields of butyl and oleic esters.

CONCLUSIONS

This work provides a molecular understanding of substrate specificities, catalytic regulation, immobilization, and industrial applications of a promiscuous cold-adapted SGNH-type lipase (HaSGNH1) from H. arcticus. This is the first analysis on biodiesel and flavor synthesis using a cold-adapted halophilic SGNH-type lipase from a Halocynthiibacter species.

Enhanced butyrate production by transition metal particles during the food waste fermentation

Butyrate is an important precursor for fine chemicals and biofuels. The aim of this study is to investigate butyrate production as affected by transition metal addition of food waste fermentation including, nickel, Raney nickel and copper particles. Performance of fermentation showed nickel particles achieved the highest butyrate concentration, 7.3 g/L, which was 38.5% higher than that in the control trial. Raney nickel also showed similar effect on the enhancement of butyrate production. However, increased dosage of transition metal particle addition led to decreased butyrate production. The theoretical link between metal-assisted dark fermentation and butyrate production was tentatively explored. Redox potential affected by nickel addition was assumed to be an essential factor for butyrate production. Microbial community analysis found Clostridium sensu stricto 11 may be the dominant functional species for butyrate production. The study demonstrates that development on transition metal catalyst may contribute to waste biorefinery for added value products/energy production.

Enhanced butyric acid production using mixed biomass of brown algae and rice straw by Clostridium tyrobutyricum ATCC25755

A brown alga Saccharina japonica and rice straw are attractive feedstock for microbial butyric acid production. However, inefficient fermentation of mannitol (a dominant component in S. japonica) and toxicity of inhibitors in lignocellulosic hydrolysate are limitations. This study demonstrated that mixed biomass with S. japonica and rice straw was effective in butyric acid production over those restrictions. Mannitol was consumed only when acetic acid was present. Notably, acetic acid was not produced but consumed along with mannitol. By mixing S. japonica and rice straw to take advantage of glucose and acetic acid in rice straw, Clostridium tyrobutyricum effectively consumed mannitol by utilizing acetic acid in hydrolysate and acetic acid derived from glucose with the enhanced butyric acid production. Furthermore, cell growth was restored owing to the decreased inhibitor concentration. The results demonstrate the potential of butyric acid production from mixed biomass of macroalgae/lignocellulose overcoming the drawbacks of single biomass.

Enhanced extraction of butyric acid under high-pressure CO2 conditions to integrate chemical catalysis for value-added chemicals and biofuels

BACKGROUND

Extractive fermentation with the removal of carboxylic acid requires low pH conditions because acids are better partitioned into the solvent phase at low pH values. However, this requirement conflicts with the optimal near-neutral pH conditions for microbial growth.

RESULTS

CO2 pressurization was used, instead of the addition of chemicals, to decrease pH for the extraction of butyric acid, a fermentation product of Clostridium tyrobutyricum, and butyl butyrate was selected as an extractant. CO2 pressurization (50 bar) improved the extraction efficiency of butyric acid from a solution at pH 6, yielding a distribution coefficient (D) 0.42. In situ removal of butyric acid during fermentation increased the production of butyric acid by up to 4.10 g/L h, an almost twofold increase over control without the use of an extraction process.

CONCLUSION

In situ extraction of butyric acid using temporal CO2 pressurization may be applied to an integrated downstream catalytic process for upgrading butyric acid to value-added chemicals in an organic solvent.

Industrial production of acetone and butanol by fermentation-100 years later

Microbial production of acetone and butanol was one of the first large-scale industrial fermentation processes of global importance. During the first part of the 20th century, it was indeed the second largest fermentation process, superseded in importance only by the ethanol fermentation. After a rapid decline after the 1950s, acetone-butanol-ethanol (ABE) fermentation has recently gained renewed interest in the context of biorefinery approaches for the production of fuels and chemicals from renewable resources. The availability of new methods and knowledge opens many new doors for industrial microbiology, and a comprehensive view on this process is worthwhile due to the new interest. This thematic issue of FEMS Microbiology Letters, dedicated to the 100th anniversary of the first industrial exploitation of Chaim Weizmann's ABE fermentation process, covers the main aspects of old and new developments, thereby outlining a model development in biotechnology. All major aspects of industrial microbiology are exemplified by this single process. This includes new technologies, such as the latest developments in metabolic engineering, the exploitation of biodiversity and discoveries of new regulatory systems such as for microbial stress tolerance, as well as technological aspects, such as bio- and down-stream processing.

Industrial production of acetone and butanol by fermentation—100 years later.