Abstract
BackgroundC1 substrates (such as formate and methanol) are promising feedstock for biochemical/biofuel production. Numerous studies have been focusing on engineering heterologous pathways to incorporate C1 substrates into biomass, while the engineered microbial hosts often demonstrate inferior fermentation performance due to substrate toxicity, metabolic burdens from engineered pathways, and poor enzyme activities. Alternatively, exploring native C1 pathways in non-model microbes could be a better solution to address these challenges.ResultsAn oleaginous fungus, Umbelopsis isabellina, demonstrates an excellent capability of metabolizing formate to promote growth and lipid accumulation. By co-feeding formate with glucose at a mole ratio of 3.9:1, biomass and lipid productivities of the culture in 7.5 L bioreactors were improved by 20 and 70%, respectively. 13C-metabolite analysis, genome annotations, and enzyme assay further discovered that formate not only provides an auxiliary energy source [promoting NAD(P)H and ATP] for cell anabolism, but also contributes carbon backbones via folate-mediated C1 pathways. More interestingly, formate addition can tune fatty acid profile and increase the portion of medium-chain fatty acids, which would benefit conversion of fungal lipids for high-quality biofuel production. Flux balance analysis further indicates that formate co-utilization can power microbial metabolism to improve biosynthesis, particularly on glucose-limited cultures.ConclusionThis study demonstrates Umbelopsis isabellina’s strong capability for co-utilizing formate to produce biomass and enhance fatty acid production. It is a promising non-model platform that can be potentially integrated with photochemical/electrochemical processes to efficiently convert carbon dioxide into biofuels and value-added chemicals.
Highlights
C1 substrates are promising feedstock for biochemical/biofuel production
We focus on an oleaginous fungus, Umbelopsis isabellina, that has demonstrated the capability to co-utilize formate and other carbon sources for growth and lipid accumulation
The fungal culture on 13C-formate supplemented with yeast extract shows that eight amino acids were detected with significant labeling extent (Fig. 2a)
Summary
C1 substrates (such as formate and methanol) are promising feedstock for biochemical/biofuel production. Microbial one-carbon (C1) metabolism plays a critical role in global carbon cycles [1]. Key C1 molecules include carbon dioxide, methane, carbon monoxide, and methanol. Among these C1 compounds, CO2 is one of the most abundant greenhouse gases in the Earth’s atmosphere, which contributes up to 26% of the global greenhouse effect [2]. Numerous studies have been conducted on microbial C1 metabolism, such as autotrophic CO2 fixation, and methylotrophic or methanotrophic carbon utilization Autotrophic CO2 fixation faces challenges including mass transfer limitation, low metabolic rate of adenosine triphosphate (ATP)/reduced nicotinamide adenine dinucleotide [NAD(P)H] generations, and poor enzymatic synthesis activities. Formate, a stable C1 compound [6], can be generated from CO2 using electrochemical
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