Engineering Acetobacterium woodii for the production of isopropanol and acetone from carbon dioxide and hydrogen

Unlocking the potential of one-carbon gases (CO2, CO) for concomitant bioproduction of β-carotene and lipids

This study investigates the use of a Yarrowia lipolytica strain for the bioconversion of syngas-derived acetic acid into β-carotene and lipids. A two-stage process was employed, starting with the acetogenic fermentation of syngas by Clostridium aceticum, metabolising CO, CO2, H2, to produce acetic acid, which is then utilized by Y. lipolytica for simultaneous lipid and β-carotene synthesis. The research demonstrates that acetic acid concentration plays a pivotal role in modulating lipid profiles and enhancing β-carotene production, with increased acetic acid consumption leading to higher yields of these compounds. This approach showcases the potential of using one-carbon gases as substrates in bioprocesses for generating valuable bioproducts, providing a sustainable and cost-effective alternative to more conventional feedstocks and substrates, such as sugars.

Recent advances in applying omic technologies for studying acetic acid bacteria in industrial vinegar production: A comprehensive review

Vinegar and related bioproducts containing acetic acid as the main component are among the most appreciated fermented foodstuffs in numerous European and Asian countries because of their exceptional organoleptic and bio-healthy properties. Regarding the acetification process and obtaining of final products, there is still a lack of knowledge on fundamental aspects, especially those related to the study of biodiversity and metabolism of the present microbiota. In this context, omic technologies currently allow for the massive analysis of macromolecules and metabolites for the identification and characterization of these microorganisms working in their natural media without the need for isolation. This review approaches comprehensive research on the application of omic tools for the identification of vinegar microbiota, mainly acetic acid bacteria, with subsequent emphasis on the study of the microbial diversity, behavior, and key molecular strategies used by the predominant groups throughout acetification. The current omics tools are enabling both the finding of new vinegar microbiota members and exploring underlying strategies during the elaboration process. The species Komagataeibacter europaeus may be a model organism for present and future research in this industry; moreover, the development of integrated meta-omic analysis may facilitate the achievement of numerous of the proposed milestones. This work might provide useful guidance for the vinegar industry establishing the first steps towards the improvement of the acetification conditions and the development of new products with sensory and bio-healthy profiles adapted to the agri-food market.

Isopropanol production via the thermophilic bioconversion of sugars and syngas using metabolically engineered Moorella thermoacetica

BACKGROUND

Isopropanol (IPA) is a commodity chemical used as a solvent or raw material for polymeric products, such as plastics. Currently, IPA production depends largely on high-CO2-emission petrochemical methods that are not sustainable. Therefore, alternative low-CO2 emission methods are required. IPA bioproduction using biomass or waste gas is a promising method.

RESULTS

Moorella thermoacetica, a thermophilic acetogenic microorganism, was genetically engineered to produce IPA. A metabolic pathway related to acetone reduction was selected, and acetone conversion to IPA was achieved via the heterologous expression of secondary alcohol dehydrogenase (sadh) in the thermophilic bacterium. sadh-expressing strains were combined with acetone-producing strains, to obtain an IPA-producing strain. The strain produced IPA as a major product using hexose and pentose sugars as substrates (81% mol-IPA/mol-sugar). Furthermore, IPA was produced from CO, whereas acetate was an abundant byproduct. Fermentation using syngas containing both CO and H2 resulted in higher IPA production at the specific rate of 0.03 h-1. The supply of reducing power for acetone conversion from the gaseous substrates was examined by supplementing acetone to the culture, and the continuous and rapid conversion of acetone to IPA showed a sufficient supply of NADPH for Sadh.

CONCLUSIONS

The successful engineering of M. thermoacetica resulted in high IPA production from sugars. M. thermoacetica metabolism showed a high capacity for acetone conversion to IPA in the gaseous substrates, indicating acetone production as the bottleneck in IPA production for further improving the strain. This study provides a platform for IPA production via the metabolic engineering of thermophilic acetogens.

Heterologous Production of Isopropanol Using Metabolically Engineered Acetobacterium woodii Strains

The depletion of fossil fuel resources and the CO2 emissions coupled with petroleum-based industrial processes present a relevant issue for the whole of society. An alternative to the fossil-based production of chemicals is microbial fermentation using acetogens. Acetogenic bacteria are able to metabolize CO or CO2 (+H2) via the Wood-Ljungdahl pathway. As isopropanol is widely used in a variety of industrial branches, it is advantageous to find a fossil-independent production process. In this study, Acetobacterium woodii was employed to produce isopropanol via plasmid-based expression of the enzymes thiolase A, CoA-transferase, acetoacetate decarboxylase and secondary alcohol dehydrogenase. An examination of the enzymes originating from different organisms led to a maximum isopropanol production of 5.64 ± 1.08 mM using CO2 + H2 as the carbon and energy source. To this end, the genes thlA (encoding thiolase A) and ctfA/ctfB (encoding CoA-transferase) of Clostridium scatologenes, adc (encoding acetoacetate decarboxylase) originating from C. acetobutylicum and sadH (encoding secondary alcohol dehydrogenase) of C. beijerinckii DSM 6423 were employed. Since bottlenecks in the isopropanol production pathway are known, optimization of the strain was investigated, resulting in a 2.5-fold increase in isopropanol concentration.

Effect of pH and medium composition on chain elongation with Megasphaera hexanoica producing C4-C8 fatty acids

Introduction

Chain elongation technology, which involves fermentation with anaerobic bacteria, has gained attention for converting short and medium chain substrates into valuable and longer-chain products like medium chain fatty acids (MCFAs). In the recent past, the focus of studies with pure chain elongating cultures was on species of other genera, mainly Clostridium kluyveri. Recently, other chain elongators have been isolated that deserve further research, such as Megasphaera hexanoica.

Methods

In this study, batch studies were performed in bottles with two different media to establish the optimal conditions for growth of M. hexanoica: (a) a medium rich in different sources of nitrogen and (b) a medium whose only source of nitrogen is yeast extract. Also, batch bioreactor studies at pH values of 5.8, 6.5 and 7.2 were set up to study the fermentation of lactate (i.e., electron donor) and acetate (i.e., electron acceptor) by M. hexanoica.

Results and discussion

Batch bottle studies revealed the yeast extract (YE) containing medium as the most promising in terms of production/cost ratio, producing n-caproate rapidly up to 2.62 ± 0.24 g/L. Subsequent bioreactor experiments at pH 5.8, 6.5, and 7.2 confirmed consistent production profiles, yielding C4-C8 fatty acids. A fourth bioreactor experiment at pH 6.5 and doubling both lactate and acetate concentrations enhanced MCFA production, resulting in 3.7 g/L n-caproate and 1.5 g/L n-caprylate. H2 and CO2 production was observed in all fermentations, being especially high under the increased substrate conditions. Overall, this study provides insights into M. hexanoica's behavior in lactate-based chain elongation and highlights optimization potential for improved productivity.

Production of biofuels from C1 -gases with Clostridium and related bacteria-Recent advances

Clostridium spp. are suitable for the bioconversion of C₁ -gases (e.g., CO₂ , CO and syngas) into different bioproducts. These products can be used as biofuels and are reviewed here, focusing on ethanol, butanol and hexanol, mainly. The production of higher alcohols (e.g., butanol and hexanol) has hardly been reviewed. Parameters affecting the optimization of the bioconversion process and bioreactor performance are addressed as well as the pathways involved in these bioconversions. New aspects, such as mixotrophy and sugar versus gas fermentation, are also reviewed. In addition, Clostridia can also produce higher alcohols from the integration of the Wood-Ljungdahl pathway and the reverse ß-oxidation pathway, which has also not yet been comprehensively reviewed. In the latter process, the acetogen uses the reducing power of CO/syngas to reduce C₄ or C₆ fatty acids, previously produced by a chain elongating microorganism (commonly Clostridium kluyveri), into the corresponding bioalcohol.

Developing a genetic engineering method for Acetobacterium wieringae to expand one-carbon valorization pathways

BACKGROUND

Developing new bioprocesses to produce chemicals and fuels with reduced production costs will greatly facilitate the replacement of fossil-based raw materials. In most fermentation bioprocesses, the feedstock usually represents the highest cost, which becomes the target for cost reduction. Additionally, the biorefinery concept advocates revenue growth from the production of several compounds using the same feedstock. Taken together, the production of bio commodities from low-cost gas streams containing CO, CO₂, and H₂, obtained from the gasification of any carbon-containing waste streams or off-gases from heavy industry (steel mills, processing plants, or refineries), embodies an opportunity for affordable and renewable chemical production. To achieve this, by studying non-model autotrophic acetogens, current limitations concerning low growth rates, toxicity by gas streams, and low productivity may be overcome. The Acetobacterium wieringae strain JM is a novel autotrophic acetogen that is capable of producing acetate and ethanol. It exhibits faster growth rates on various gaseous compounds, including carbon monoxide, compared to other Acetobacterium species, making it potentially useful for industrial applications. The species A. wieringae has not been genetically modified, therefore developing a genetic engineering method is important for expanding its product portfolio from gas fermentation and overall improving the characteristics of this acetogen for industrial demands.

RESULTS

This work reports the development and optimization of an electrotransformation protocol for A. wieringae strain JM, which can also be used in A. wieringae DSM 1911, and A. woodii DSM 1030. We also show the functionality of the thiamphenicol resistance marker, catP, and the functionality of the origins of replication pBP1, pCB102, pCD6, and pIM13 in all tested Acetobacterium strains, with transformation efficiencies of up to 2.0 × 10³ CFU/μg_DNA. Key factors affecting electrotransformation efficiency include OD₆₀₀ of cell harvesting, pH of resuspension buffer, the field strength of the electric pulse, and plasmid amount. Using this method, the acetone production operon from Clostridium acetobutylicum was efficiently introduced in all tested Acetobacterium spp., leading to non-native biochemical acetone production via plasmid-based expression.

CONCLUSIONS

A. wieringae can be electrotransformed at high efficiency using different plasmids with different replication origins. The electrotransformation procedure and tools reported here unlock the genetic and metabolic manipulation of the biotechnologically relevant A. wieringae strains. For the first time, non-native acetone production is shown in A. wieringae.

Biological production of 2-propanol from propane using a metabolically engineered type I methanotrophic bacterium

2-Propanol is a widely used industrial solvents. Herein, we employed a unique feature of type I methanotrophic bacterium Methylotuvimicrobium alcaliphilum 20Z possessing only particulate methane monooxygenase (pMMO) for one-step direct production of pure 2-propanol from propane. By maintaining cell growth on glycerol, and after deletion of both Ca²⁺-dependent and La³⁺-dependent methanol dehydrogenases, propane was converted to 2-propanol by pMMO. Although most of the 2-propanol produced was further oxidized to acetone, deletion of active alcohol dehydrogenase, concomitant with synchronous overexpression of secondary alcohol dehydrogenase, significantly inhibited such undesirable oxidation. As a result, a remarkable enhancement (263 mg/L) of 2-propanol was achieved for 120 h by increasing cell growth with a supply of 50% (v/v) propane in headspace. This is the first demonstration to develop an engineered methanotrophic strain for the one-step direct production of pure 2-propanol from propane using one-phase cultivation without the supply of chemical inhibitors or additional reducing-power sources.