Background: Yarrowia lipolytica is an unconventional yeast with a huge industrial potential. Despite many advantages for biotechnological applications, it possesses enormous demand for oxygen, which is a bottleneck in large scale production. In this study a codon optimized bacterial hemoglobin from Vitreoscilla stercoraria (VHb) was overexpressed in Y. lipolytica for efficient growth and erythritol synthesis from glycerol in low-oxygen conditions. Erythritol is a natural sweetener produced by Y. lipolytica under high osmotic pressure and at low pH, and this process requires high oxygen demand. Results: Under these conditions the VHb overexpressing strain showed mostly yeast-type cells resulting in 83% higher erythritol titer in shake-flask experiments. During a bioreactor study the engineered strain showed higher erythritol productivity (Q_ERY = 0.38 g/l h) and yield (Y_ERY = 0.37 g/g) in comparison to the control strain (Q_ERY = 0.30 g/l h, Y_ERY = 0.29 g/g). Moreover, low stirring during the fermentation process resulted in modest foam formation. Conclusions: This study showed that overexpression of VHb in Y. lipolytica allows for dynamic growth and efficient production of a value-added product from a low-value substrate.

Erythritol is a polyol produced by Yarrowia lipolytica under hyperosmotic stress. In this study, the osmo-sensitive strain Y. lipolytica yl-hog1Δ was subjected to stress, triggered by a high concentration of carbon sources. The strain thrived on 0.75 M erythritol medium, while the same concentrations of glucose and glycerol proved to be lethal. The addition of 0.1 M erythritol to the medium containing 0.75 M glucose or glycerol allowed the growth of yl-hog1Δ. Supplementation with other potential osmolytes such as mannitol or L-proline did not have a similar effect. To examine whether the osmoprotective effect might be related to erythritol accumulation, we deleted two genes involved in erythritol utilization, the transcription factor Euf1 and the enzyme erythritol dehydrogenase Eyd1. The strain eyd1Δ yl hog1Δ, which lacked the erythritol utilization enzyme, reacted to the erythritol supplementation significantly better than yl-hog1Δ. On the other hand, the strain euf1Δ yl-hog1Δ became insensitive to supplementation, and the addition of erythritol could no longer improve the growth of this strain in hyperosmotic conditions. This indicates that Euf1 regulates additional, still unknown genes involved in erythritol metabolism.

The unconventional yeast Yarrowia lipolytica is used to produce erythritol from glycerol. In this study, the role of the erythrose reductase (ER) homolog YALI0B07117g in erythritol synthesis was analyzed. The deletion of the gene resulted in an increased production of mannitol (308%) and arabitol (204%) before the utilization of these polyols began. The strain overexpressing the YALI0B07117g gene was used to increase the erythritol yield from glycerol as a sole carbon source in batch cultures, resulting in a yield of 0.4 g/g. The specific consumption rate (qs) increased from 5.83 g/g/L for the WT strain to 8.49 g/g/L for the modified strain and the productivity of erythritol increased from 0.28 g/(L h) for the A101 strain to 0.41 g/(L h) for the modified strain. The application of the research may prove positive for shortening the cultivation time due to the increased rate of consumption of the substrate combined with the increased parameters of erythritol synthesis.

Background: Yarrowia lipolytica is a dimorphic fungus, which switches from yeast to filament form in response to environmental conditions. For industrial purposes it is important to lock cells in the yeast or filamentous form depending on the fermentation process. yl-Hog1 kinase is a key component of the HOG signaling pathway, responsible for activating the osmotic stress response. Additionally, deletion of yl-Hog1 leads to increased filamentation in Yarrowia lipolytica, but causes significant sensitivity to osmotic stress induced by a high concentration of a carbon source. Results: In this study, we tested the effect of point mutations on the function of yl-Hog1 protein kinase. The targets of modification were the phosphorylation sites (T171A-Y173A) and the active center (K49R). Introduction of the variant HOG1-49 into the hog1∆ strain partially improved growth under osmotic stress, but did not recover the yeast-like shape of the cells. The HOG1-171/173 variant was not functional, and its introduction further weakened the growth of hog1∆ strains in hyperosmotic conditions. To verify a genetic modification in filament form, we developed a new system based on green fluorescent protein (GFP) for easier screening of proper mutants. Conclusions: These results provide new insights into the functions of yl-Hog1 protein in dimorphic transition and constitute a good starting point for further genetic modification of Y. lipolytica in filament form.

The progressive deployment of renewable energy systems has engendered a considerable increase in the generation of glycol-based coolant waste, specifically ethylene glycol (EG) and propylene glycol (PG), thereby raising significant environmental apprehensions. This review analyses the critical environmental challenge and examines the feasibility of microbial degradation as a viable and sustainable alternative to glycol waste treatment, while highlighting significant gaps in current hazardous glycol waste management practices. Present waste management practices are largely founded on incineration or membrane filtration approaches, both of which exhibit significant energy demands and inefficiencies in large-scale waste handling. Reported performance ranges from >99% EG recovery at 10–16 kWh/m³ by electrodialysis and 80–95% recovery at 2–4 MJ/kg by vacuum distillation, to ~17 MJ/kg combustion heat from incineration; biological methods, though promising, currently operate below 10% glycol concentration, an order of magnitude below the 10–100% range in real coolants. We analyze the current understanding of metabolic pathways involved in glycol biodegradation, drawing on the peer-reviewed literature, bioinformatics, and patent databases. Special attention is given to the challenges of high glycol concentrations in industrial coolants and the formation of toxic oxidation products during thermal aging. The review also explores recent advances in genetic engineering approaches to enhance microbial degradation efficiency. Finally, we discuss the potential integration of biological recycling methods into existing waste management systems and future prospects for converting glycol waste into value-added products through microbial biotransformation.

The increasing volume of sewage sludge generated by wastewater treatment plants poses a major environmental and economic challenge, highlighting the need for sustainable treatment and valorization strategies. Hydrothermal carbonization (HTC) converts wet biomass, such as sewage sludge, into value-added products; however, the aqueous post-reaction phase (HTC-AP) remains largely underutilized. The presented study aimed to evaluate HTC-AP derived from sewage sludge as a medium for Yarrowia lipolytica to produce microbial lipids, thereby addressing the gap in integrated sludge-to-value bioprocesses. HTC was performed at 180-300 °C for 60-120 min to generate liquid fractions, which were subsequently tested as substrates for lipid biosynthesis by different Y. lipolytica strains. The composition of HTC-AP, strains tolerance, volatile fatty acid (VFA) assimilation, lipid accumulation, and fatty acid profiles were assessed. In addition, techno-economic and life cycle assessments were conducted, supported by integrated experimental and process modeling approaches. The HTC liquid fraction contained primarily acetic (4.9 g/L) and propionic acid (6.6 g/L), together with phenolic and heterocyclic compounds, which could potentially have an inhibitory effect. Among the tested strains, Yarrowia lipolytica A101 and the double mutant ΔEYD DGA1 (knock-out of erythritol dehydrogenase and overexpression of diacylglycerol acyltransferase) exhibited the highest tolerance to HTC-AP and effectively assimilated VFAs, particularly under HTC conditions of 180 °C for 60 min. Lipid profiles showed the oleic (C18:1) and linoleic (C18:2) acids being produced more predominantly, regardless of the cultivation scale. Techno-economic analysis demonstrated the feasibility of the integrated process, yielding an estimated net profit of approximately $292.5 per ton of treated sludge (TT180-RT60), while life cycle assessment indicated a relatively low environmental impact of ∼0.38 kg CO₂-eq per kg of produced lipids. These findings demonstrate that coupling hydrothermal processing with metabolically engineered Y. lipolytica fermentation allows for an effective sewage sludge valorization. Furthermore, integrated process modeling facilitates scale-up and industrial implementation, while additional optimizations such as pre-dewatering and heat recovery may further improve process efficiency and environmental performance.