Again ($98.8 million to use millennia-old bacteria to transform CO2 into biofuels)

Again (also SecondCircle Bio), a biotech company founded in Denmark in 2020, develops a gas fermentation technology that uses thermophilic bacteria in a bioreactor to transform carbon dioxide (CO₂) from flue gasses into biofuels like acetate, acetone, and ethanol. This process not only cuts down on CO₂ emissions, but it also makes green, sustainable fuels that can replace chemicals made from traditional fossil fuels.

Table of contents

Challenges

Carbon emissions and CO₂ capture

Industrial carbon emissions contribute significantly to climate change. Apart from the traditional approach of carbon capture and storage from industrial flue gas, emerging technologies, such as Direct Air Capture (DAC), enhanced weathering, and Direct Ocean Capture, can remove excessive atmospheric CO₂. However, storing captured CO₂ underground has long-term ecological risks and a lack of economic viability, thus being increasingly viewed as an unsustainable way. However, converting captured CO₂ to value-added chemicals or sustainable fuels, instead of geological storage, is attracting more attention. Among technologies of carbon neutral fuels, microbial fermentation offers a circular solution.

Moorella thermoacetica for CO₂ fixation

Acetogenic bacteria grow by consuming gaseous CO₂ (or CO). The process fixes CO₂. Thermophilic bacteria for CO₂ fixation at typical temperatures between 45 ºC and 80 ºC are of particular interest because they reduce risk of contamination with unwanted microorganisms, use less energy for cooling the fermentation system, have a faster production rate due to the advantageous thermodynamics, and lower capital and operational expenditures.

Moorella thermoacetica is a type of thermophilic bacteria that can turn CO₂ gas into acetone and other useful chemicals. So, they have attracted significant interest in the applications in clean technology, renewable energy, and the production of fuels and other valuable chemicals.

Moorella thermoacetica is very good at fixing CO₂, but its growth rate is slow, which makes it less effective at fixing CO₂. Moorella thermoacetica is also sensitive to fluctuations in the gas supply and gradients in the industrial production bioreactor. If there aren’t enough nutrients or CO₂ gas in the bioreactor, Moorella thermoacetica can die or sporulate. This makes subcultures inactive and decreases the overall efficiency significantly.

Again Technology

Again has developed a biotechnology to increase the growth of a Moorella thermoacetica by deleting SpoOA gene and/or introducing genes to express a variant of SinR in the bacterium. This gene modification has increased the growth rates and decreased the lag phase duration of the Moorella thermoacetica, increasing their CO₂ fixation and biochemical production efficiency. Through the optimization of trace elements in the fermentation medium and operational steps, Again uses Moorella thermoacetica for anaerobic microbial fermentation to efficiently convert CO₂ into organic chemicals, transforming emissions into marketable products like biofuels or bioplastics.

Thermophilic bacteria fix CO2 to produce biofuel. — Again uses thermophilic bacteria fix CO2 to produce biofuel.

How Again increases the growth of Moorella thermoacetica

The growth of a bacterial culture can be divided into four distinct phases: lag phase, log phase, stationary phase, and death phase.

Lag phase

This is the first stage of bacterial growth, when the number of bacteria stays the same as they get used to the conditions of the growth medium. They increase in size and synthesize enzymes, RNA, and other molecules necessary for cell division and population growth under their new environmental conditions. How long the lag phase lasts depends a lot on where the bacteria came from and how healthy the bacteria cells are.

Log phase

In this phase, the population of bacteria grows logarithmically.

Stationary phase

In this phase, the bacterial population stays the same because the nutrient supply is depleted, so growth stops.

Death phase

This is the last stage of growth, when all the nutrients have been used up and the number of cells starts to go down.

Again has increased the growth of a Moorella species bacteria by modifications of the genes that code for SpoOA and SinR to make Moorella thermoacetica grow faster. This makes the bacteria more efficient at fixing CO₂ and producing biochemicals (see WO2023036823A1).

SpoOA (Stage 0 sporulation protein A homolog) is a protein that regulates sporulation, the process by which bacteria form spores in response to environmental stress. SpoOA gene deletion can prevent sporulation.

The SinR (HTH-type transcriptional regulator SinR) is a protein capable of binding to specific DNA sequences to regulate gene bacterial expression in response to nutrient depletion at the end of vegetative growth. For example, the SinR can function as a repressor of SpoOA.

Again has introduced genetic modifications into the bacterium that allow it to express a variant of SinR, which aids bacteria in adapting more quickly to the new environment, potentially shortening the lag phase boosting their growth rates.

The SinR variant has at least 90% sequence identity with SEQ ID NO: 2 and an amino acid other than valine (V) at the position corresponding to position 198 in SEQ ID NO: 2. The amino acid at the position corresponding to position 198 in SEQ ID NO: 2 is phenylalanine (F).

A V198F mutation in SinR decreases the duration of Moorella thermoacetica’s lag phase (it leads to a more rapid recovery from resting state) upon inoculation into fresh medium following a longer incubation period. Moreover, the V198F in Moorella thermoacetica SinR may affect the protein’s stability, affinity for the anti-repressor SinI, and/or ability to oligomerize.

How Again converts CO₂ into organic chemicals

Again’s bioreactor system can be integrated with industrial infrastructure. The bioreactor with carbon capture units of the flue gas enables direct conversion of scrubbed CO₂ into biochemicals. Industrial waste heat can maintain thermophilic reactor temperatures, reducing energy costs. The diagram below illustrates the process flow of industrial-scale CO₂ conversion into organic chemicals.

Again’s industrial scale of CO₂ conversion into organic chemicals via Moorella thermoacetica (ref. WO2024074714A1).

Industrial flue gases are captured and undergo filtration to remove contaminants like sulfur compounds, followed by adjustments of their composition for microbial uptake. Moorella thermoacetica requires an H₂/CO₂ ratio of 80:20, which is achieved through gas blending. The gases are then humidified and cooled to match bioreactor operating temperatures (55–65 ºC), ensuring seamless integration into the fermentation system.

Next, bioreactor setup and inoculation are critical. Industrial-scale bioreactors (5–80 m³ capacity) are constructed from corrosion-resistant materials like stainless steel, equipped with gas spargers for efficient gas dispersion and agitation systems to maintain homogeneity. Temperature is tightly controlled using external heating jackets. Acetogenic bacteria are pre-cultured in seed reactors using nutrient-rich media, achieving high biomass density before transfer to the main reactor. This step ensures robust microbial populations ready for gas conversion.

The dual-phase fermentation strategy is executed in two stages. In the biomass propagation phase, hexoses like fructose are used to rapidly grow microbial cells under low-magnesium conditions (0.15–0.30 mM), preventing premature product formation. Once optimal biomass density is reached, the system switches to gas-fed production. CO₂ replaces sugars as the carbon source, while magnesium levels are increased 10–15 fold (10–40 mM) to stabilize ATP-driven pathways. Selenium concentrations are simultaneously elevated (30–50 µM) to enhance selenoenzyme activity, driving efficient carbon fixation.

Real-time monitoring and automation ensure process stability. Sensors track gas consumption rates, pH, redox potential, and biomass density, while automated controls adjust gas flow, nutrient dosing, and agitation speed. For instance, if CO₂ uptake slows, the system increases gas sparging or adjusts the H₂/CO₂ ratio. Unused gases are recirculated to improve carbon utilization efficiency, achieving up to 80% conversion rates.

Downstream processing involves separating microbial biomass via centrifugation or filtration, with cells recycled to seed new batches. Target products like acetate or ethanol are purified using distillation or membrane technologies, yielding 20–30 g/L of acetate or 10–15 g/L of ethanol. Residual solids are valorized into biogas or fertilizers, minimizing waste.

CO₂ conversion efficiency of Again technology

Again’s modular bioreactors, scaling from pilot (5 m³) to full industrial (80 m³) levels, can convert 1 ton of CO₂ into 0.5 – 0.7 tons of organic chemicals. By meeting carbon credit standards (e.g., EU ETS), the technology offers industries a compliant pathway to decarbonization, merging ecological responsibility with economic viability.

Again Patent

WO2023036823A1 Increasing growth of a co2 fixing thermophile bacterium
WO2024074714A1 Optimised fermentation of anaerobic bacteria

Again Technology Applications

Production of carbon-negative chemicals

Again converts CO₂ into essential chemicals such as acetic acid, ethyl acetate, and acetone. These chemicals are foundational to manufacturing adhesives, solvents, plastics, textiles, cosmetics, and other industrial products. Their bio-process is energy-efficient and produces chemicals with a carbon footprint significantly lower than traditional petrochemical routes.

Fertilizer manufacturing

Their technology also produces key fertilizer components, addressing the agricultural sector’s need for sustainable inputs while reducing greenhouse gas emissions associated with conventional fertilizer production.

Materials and polymers

The platform can be used to manufacture clean, sustainable materials such as polymers and textiles, which are critical for various manufacturing sectors reliant on carbon-based feedstocks.

Again Products

Again has developed several projects:

CPH–1 (Copenhagen, Denmark)

Operational since 2023, this pilot plant captures 1 ton of CO₂ daily from a wastewater treatment facility, converting it into acetate and acetic acid. It has logged over 17,000 operational hours and serves as a model for scalability.

TXS–1 (Texas City, US)

A commercial facility set to produce 20,000 tons of glacial acetic acid annually starting in late 2025, in partnership with HELM AG for global distribution. Expected to abate 32,000 tons of CO₂ over its lifetime.

NOR–1 (Porsgrunn, Norway)

Part of the EU-funded PyroCO₂ project (€43M grant), this plant will produce 4,000 tons of green acetone annually using 10,000 tons of CO₂, targeting industries like adhesives and plastics.

Again Technology Readiness Level (TRL)

Again’s technology is estimated at TRL 8-9, supported by operational pilot and commercial-scale facilities (CPH–1, TXS–1, and NOR–1), industry partnerships, and market-ready products.

Again Funding

Again has raised a total of $98.8M in funding over 4 rounds:

a Pre-Seed round
a Grant round
a Seed round
a Series A round

Their latest funding was raised on Jul 17, 2024 from a Series A round.

Again Investors

Again is funded by 8 investors:

KOMPAS VC and Google Ventures are the most recent investors.

The funding rounds by investors of Again.

Again Founder

Torbjørn Ølshøj Jensen, Alex Toftgaard Nielsen, Maximilian Kufner, and Stephanie Redl are Co-Founders.

Again CEO

Torbjørn Ølshøj Jensen is CEO.