Carbon dioxide bioconversion into single cell oils (lipids) in two reactors inoculated with Acetobacterium woodii and Rhodosporidium toruloides

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.

Sequential bioconversion of C1-gases (CO, CO2, syngas) into lipids, through the carboxylic acid platform, with Clostridium aceticum and Rhodosporidium toruloides

Syngas (CO, CO2, H2) was effectively bioconverted into lipids in a two-stage process. In the first stage, C1-gases were bioconverted into acetic acid by the acetogenic species Clostridium aceticum through the Wood-Ljungdahl metabolic pathway in a stirred tank bioreactor, reaching a maximum acetic acid concentration of 11.5 g/L, with a production rate of 0.05 g/L·h. Throughout this experiment, samples were extracted at different periods, i.e., different concentrations, to be used in the second stage, aiming at the production of lipids from acetic acid. The yeast Rhodosporidium toruloides, inoculated in the acetogenic medium, was able to efficiently accumulate lipids from acetic acid generated in the first stage. The best results, in terms of lipid content, dry biomass, biomass yield (Y(X/S)) and lipid yield (Y(L/S)) were 39.5% g/g dry cell weight, 3 g/L, 0.35 and 0.107, respectively. In terms of abundance, the lipid profile followed the order: C18:1 > C16:0 > C18:2 > C18:0 > Others. Experiments were also performed to determine the toxicity exerted by high concentrations of acetic acid on R. toruloides, resulting in inhibition at initial acid concentrations around 18 g/L leading to a higher lag phase and being lethal to the yeast at initial acetic acid concentrations around 22 g/L and above. This research paves the way for a novel method of growing oleaginous yeasts to produce sustainable biofuels from syngas or C1-pollutant gases.

Integrated fermentative process for lipid and β-carotene production from acetogenic syngas fermentation using an engineered oleaginous Yarrowia lipolytica yeast

An engineered Yarrowia lipolytica strain was successfully employed to produce β-carotene and lipids from acetic acid, a product of syngas fermentation by Clostridium aceticum. The strain showed acetic acid tolerance up to concentrations of 20 g/L. Flask experiments yielded a peak lipid content of 33.7 % and β-carotene concentration of 13.6 mg/g under specific nutrient conditions. The study also investigated pH effects on production in bioreactors, revealing optimal lipid and β-carotene contents at pH 6.0, reaching 22.9 % and 44 mg/g, respectively. Lipid profiles were consistent across experiments, with C18:1 being the dominant compound at approximately 50 %. This research underscores a green revolution in bioprocessing, showing how biocatalysts can convert syngas, a potentially polluting byproduct, into valuable β-carotene and lipids with a Y. lipolytica strain.

A biotechnological roadmap for decarbonization systems combined into bioenergy production: Prelude of environmental life-cycle assessment

Decarbonization has become a critical issue in recent years due to rising energy demands and diminishing oil resources. Decarbonization systems based on biotechnology have proven to be a cost-effective and environmentally benign technique of lowering carbon emissions. Bioenergy generation is an environmentally friendly technique for mitigating climate change in the energy industry, and it is predicted to play an important role in lowering global carbon emissions. This review essentially provides a new perspective on the unique biotechnological approaches and strategies based decarbonization pathways. Furthermore, the application of genetically engineered microbes in CO₂ biomitigation and energy generation is particularly emphasized. The production of biohydrogen and biomethane via anaerobic digestion techniques has been highlighted in the perspective. In this review, role of microorganisms in bioconversion of CO₂ into different types of bioproducts such as biochemical, biopolymers, biosolvents and biosurfactant was summarized. The current analysis, which includes an in-depth discussion of a biotechnology-based roadmap for the bioeconomy, provides a clear picture of sustainability, forthcoming challenges, and perspectives.

Bioconversion of cellulose into bisabolene using Ruminococcus flavefaciens and Rhodosporidium toruloides

In this study, organic acids were demonstrated as a promising carbon source for bisabolene production by the non-conventional yeast, Rhodosporidium toruloides, at microscale with a maximum titre of 1055 ± 7 mg/L. A 125-fold scale-up of the optimal process, enhanced bisabolene titres 2.5-fold to 2606 mg/L. Implementation of a pH controlled organic acid feeding strategy at this scale lead to a further threefold improvement in bisabolene titre to 7758 mg/L, the highest reported microbial titre. Finally, a proof-of-concept sequential bioreactor approach was investigated. Firstly, the cellulolytic bacterium Ruminococcus flavefaciens was employed to ferment cellulose, yielding 4.2 g/L of organic acids. R. toruloides was subsequently cultivated in the resulting supernatant, producing 318 ± 22 mg/L of bisabolene. This highlights the feasibility of a sequential bioprocess for the bioconversion of cellulose, into biojet fuel candidates. Future work will focus on enhancing organic acid yields and the use of real lignocellulosic feedstocks to further enhance bisabolene production.

Accumulation of lipids by the oleaginous yeast Yarrowia lipolytica grown on carboxylic acids simulating syngas and carbon dioxide fermentation

Volatile fatty acids (VFAs) can be considered as low-cost carbon substrates for lipid accumulation by oleaginous yeasts. This study demonstrates that a common mixture of VFAs, typically obtained from the anaerobic fermentation of C1-gases by some acetogenic bacteria, can be used in a second aerobic fermentation with the yeast Yarrowia lipolytica to obtain lipids as precursors of biodiesel. In the batch experiments, the preference of Yarrowia lipolytica W29 for acetic acid over butyric and caproic acids was demonstrated, with the highest consumption rate reaching 0.664 g/L·h. In the bioreactor experiments, the amount initial biomass inoculated, as well as the initial acid concentration, were found to have a significant influence on the process. Though the lipid content was relatively low, it can be optimized and further improved. Oleic, linoleic and palmitic acids accounted for about 80 % of the fatty acids in the lipids, which makes them suitable for biodiesel.

Recent Trends in Biogenic Gas, Waste and Wastewater Fermentation

In recent years, the optimization of bioprocesses for the removal of pollutants from industrial biogenic gas emissions, waste and wastewater has been the focus of intensive research. Recently developed technologies not only aim to remove such pollutants, but also to valorize them, whenever possible, through their bioconversion into useful added-value products. In this domain of progressive research, lab-, pilot-, and demonstration-scale studies are dealing with the fermentation of biogenic gases (e.g., CO2, CO, and CH4), waste or wastewater to produce a range of biofuels and valuable products, based on the activity of pure or mixed cultures of native or recombinant aerobic and anaerobic bacteria, algae, or yeasts as biocatalysts. Waste can also be converted to syngas, which can subsequently be fermented as well. A broad range of bioproducts can be obtained, e.g., biofuels and several other platform chemicals and products. This environmentally-friendly biorefinery approach addresses the need to build modern societies according to the concept of a circular economy, and yields products of commercial interest. Different examples of such approaches are described in this collection of scientific reports.