A novel process-based model of microbial growth: self-inhibition in Saccharomyces cerevisiae aerobic fed-batch cultures

Extracellular Self-DNA Effects on Yeast Cell Cycle and Transcriptome during Batch Growth

The cell cycle and the transcriptome dynamics of yeast exposed to extracellular self-DNA during an aerobic batch culture on glucose have been investigated using cytofluorimetric and RNA-seq analyses. In parallel, the same study was conducted on yeast cells growing in the presence of (heterologous) nonself-DNA. The self-DNA treatment determined a reduction in the growth rate and a major elongation of the diauxic lag phase, as well as a significant delay in the achievement of the stationary phase. This was associated with significant changes in the cell cycle dynamics, with slower exit from the G0 phase, followed by an increased level of cell percentage in the S phase, during the cultivation. Comparatively, the exposure to heterologous DNA did not affect the growth curve and the cell cycle dynamics. The transcriptomic analysis showed that self-DNA exposure produced a generalized downregulation of transmembrane transport and an upregulation of genes associated with sulfur compounds and the pentose phosphate pathway. Instead, in the case of the nonself treatment, a clear response to nutrient deprivation was detected. Overall, the presented findings represent further insights into the complex functional mechanisms of self-DNA inhibition.

Extracellular DNA secreted in yeast cultures is metabolism-specific and inhibits cell proliferation

Extracellular DNA (exDNA) can be actively released by living cells and different putative functions have been attributed to it. Further, homologous exDNA has been reported to exert species-specific inhibitory effects on several organisms. Here, we demonstrate by different experimental evidence, including 1H-NMR metabolomic fingerprint, that the growth rate decline in Saccharomyces cerevisiae fed-batch cultures is determined by the accumulation of exDNA in the medium. Sequencing of such secreted exDNA represents a portion of the entire genome, showing a great similarity with extrachromosomal circular DNA (eccDNA) already reported inside yeast cells. The recovered DNA molecules were mostly single strands and specifically associated to the yeast metabolism displayed during cell growth. Flow cytometric analysis showed that the observed growth inhibition by exDNA corresponded to an arrest in the S phase of the cell cycle. These unprecedented findings open a new scenario on the functional role of exDNA produced by living cells.

Live while the DNA lasts. The role of autophagy in DNA loss and survival of diploid yeast cells during chronological aging

Aging is inevitable and affects all cell types, thus yeast cells are often used as a model in aging studies. There are two approaches to studying aging in yeast: replicative aging, which describes the proliferative potential of cells, and chronological aging, which is used for studying post-mitotic cells. While analyzing the chronological lifespan (CLS) of diploid Saccharomyces cerevisiae cells, we discovered a remarkable phenomenon: ploidy reduction during aging progression. To uncover the mechanism behind this unusual process we used yeast strains undergoing a CLS assay, looking for various aging parameters. Cell mortality, regrowth ability, autophagy induction and cellular DNA content measurements indicated that during the CLS assay, dying cells lost their DNA, and only diploids survived. We demonstrated that autophagy was responsible for the gradual loss of DNA. The nucleophagy marker activation at the start of the CLS experiment correlated with the significant drop in cell viability. The activation of piecemeal microautophagy of nucleus (PMN) markers appeared to accompany the chronological aging process until the end. Our findings emphasize the significance of maintaining at least one intact copy of the genome for the survival of post-mitotic diploid cells. During chronological aging, cellular components, including DNA, are exposed to increasing stress, leading to DNA damage and fragmentation in aging cells. We propose that PMN-dependent clearance of damaged DNA from the nucleus helps prevent genome rearrangements. However, as long as one copy of the genome can be rebuilt, cells can still survive.

Metabolic flux analysis: a comprehensive review on sample preparation, analytical techniques, data analysis, computational modelling, and main application areas

Metabolic flux analysis (MFA) quantitatively describes cellular fluxes to understand metabolic phenotypes and functional behaviour after environmental and/or genetic perturbations. In the last decade, the application of stable isotopes became extremely important to determine and integrate in vivo measurements of metabolic reactions in systems biology. 13C-MFA is one of the most informative methods used to study central metabolism of biological systems. This review aims to outline the current experimental procedure adopted in 13C-MFA, starting from the preparation of cell cultures and labelled tracers to the quenching and extraction of metabolites and their subsequent analysis performed with very powerful software. Here, the limitations and advantages of nuclear magnetic resonance spectroscopy and mass spectrometry techniques used in carbon labelled experiments are elucidated by reviewing the most recent published papers. Furthermore, we summarise the most successful approaches used for computational modelling in flux analysis and the main application areas with a particular focus in metabolic engineering.

Rewiring the Metabolic Network to Increase Docosahexaenoic Acid Productivity in Crypthecodinium cohnii by Fermentation Supernatant-Based Adaptive Laboratory Evolution

Docosahexaenoic acid (DHA, 22:6n-3) plays significant roles in enhancing human health and preventing human diseases. The heterotrophic marine dinoflagellate Crypthecodinium cohnii is a good candidate to produce high-quality DHA. To overcome the inhibition caused by the fermentation supernatant in the late fermentation stage of DHA-producing C. cohnii, fermentation supernatant-based adaptive laboratory evolution (FS-ALE) was conducted. The cell growth and DHA productivity of the evolved strain (FS280) obtained after 280 adaptive cycles corresponding to 840 days of evolution were increased by 161.87 and 311.23%, respectively, at 72 h under stress conditions and increased by 19.87 and 51.79% without any stress compared with the starting strain, demonstrating the effectiveness of FS-ALE. In addition, a comparative proteomic analysis identified 11,106 proteins and 910 differentially expressed proteins, including six stress-responsive proteins, as well as the up- and downregulated pathways in FS280 that might contribute to its improved cell growth and DHA accumulation. Our study demonstrated that FS-ALE could be a valuable solution to relieve the inhibition of the fermentation supernatant at the late stage of normal fermentation of heterotrophic microalgae.

A cytofluorimetric analysis of a Saccharomyces cerevisiae population cultured in a fed-batch bioreactor

The yeast Saccharomyces cerevisiae is a reference model system and one of the widely used microorganisms in many biotechnological processes. In industrial yeast applications, combined strategies aim to maximize biomass/product yield, with the fed-batch culture being one of the most frequently used. Flow cytometry (FCM) is widely applied in biotechnological processes and represents a key methodology to monitor cell population dynamics. We propose here an application of FCM in the analysis of yeast cell cycle along the time course of a typical S. cerevisiae fed-batch culture. We used two different dyes, SYTOX Green and SYBR Green, with the aim to better define each stage of cell cycle during S. cerevisiae fed-batch culture. The results provide novel insights in the use of FCM cell cycle analysis for the real-time monitoring of S. cerevisiae bioprocesses.

Systematic engineering of Saccharomyces cerevisiae for D-lactic acid production with near theoretical yield

D-lactic acid is a chiral three-carbon organic acid that can improve the thermostability of polylactic acid. Here, we systematically engineered Saccharomyces cerevisiae to produce D-lactic acid from glucose, a renewable carbon source, at near theoretical yield. Specifically, we screened D-lactate dehydrogenase (DLDH) variants from lactic acid bacteria in three different genera and identified the Leuconostoc pseudomesenteroides variant (LpDLDH) as having the highest activity in yeast. We then screened single-gene deletions to minimize the production of the side products ethanol and glycerol as well as prevent the conversion of D-lactic acid back to pyruvate. Based on the results of the DLDH screening and the single-gene deletions, we created a strain called ASc-d789M which overexpresses LpDLDH and contains deletions in glycerol pathway genes GPD1 and GPD2 and lactate dehydrogenase gene DLD1, as well as downregulation of ethanol pathway gene ADH1 using the L-methionine repressible promoter to minimize impact on growth. ASc-d789M produces D-lactic acid at a titer of 17.09 g/L in shake-flasks (yield of 0.89 g/g glucose consumed or 89% of the theoretical yield). Fed-batch fermentation resulted in D-lactic acid titer of 40.03 g/L (yield of 0.81 g/g glucose consumed). Altogether, our work represents progress towards efficient microbial production of D-lactic acid.

A New Model of Alcoholic Fermentation under a Byproduct Inhibitory Effect

Despite the advantages of continuous fermentation whereby ethanol is selectively removed from the fermenting broth to reduce the end-product inhibition, this process can concentrate minor secondary products to the point where they become toxic to the yeast. This study aims to develop a new mathematical model do describe the inhibitory effect of byproducts on alcoholic fermentation including glycerol, lactic acid, acetic acid, and succinic acid, which were reported as major byproducts during batch alcoholic fermentation. The accumulation of these byproducts during the different stages of batch fermentation has been quantified. The yields of total byproducts, glycerol, acetic acid, and succinic acid per gram of glucose were 0.0442, 0.023, 0.0155, and 0.0054, respectively. It was found that the concentration of these byproducts linearly increases with the increase in glucose concentration in the range of 25-250 g/L. The results have also showed that byproduct concentration has a significant inhibitory effect on specific growth coefficient (μ) whereas no effect was observed on the half-velocity constant (K _s). A new mathematical model of alcoholic fermentation was developed considering the byproduct inhibitory effect, which showed a good performance and more accuracy compared to the classical Monod model.

Predicting By-Product Gradients of Baker’s Yeast Production at Industrial Scale: A Practical Simulation Approach

Scaling up bioprocesses is one of the most crucial steps in the commercialization of bioproducts. While it is known that concentration and shear rate gradients occur at larger scales, it is often too risky, if feasible at all, to conduct validation experiments at such scales. Using computational fluid dynamics equipped with mechanistic biochemical engineering knowledge of the process, it is possible to simulate such gradients. In this work, concentration profiles for the by-products of baker’s yeast production are investigated. By applying a mechanistic black-box model, concentration heterogeneities for oxygen, glucose, ethanol, and carbon dioxide are evaluated. The results suggest that, although at low concentrations, ethanol is consumed in more than 90% of the tank volume, which prevents cell starvation, even when glucose is virtually depleted. Moreover, long exposure to high dissolved carbon dioxide levels is predicted. Two biomass concentrations, i.e., 10 and 25 g/L, are considered where, in the former, ethanol production is solely because of overflow metabolism while, in the latter, 10% of the ethanol formation is due to dissolved oxygen limitation. This method facilitates the prediction of the living conditions of the microorganism and its utilization to address the limitations via change of strain or bioreactor design or operation conditions. The outcome can also be of value to design a representative scale-down reactor to facilitate strain studies.

A General Process-Based Model for Describing the Metabolic Shift in Microbial Cell Cultures

The metabolic shift between respiration and fermentation at high glucose concentration is a widespread phenomenon in microbial world, and it is relevant for the biotechnological exploitation of microbial cell factories, affecting the achievement of high-cell-densities in bioreactors. Starting from a model already developed for the yeast Saccharomyces cerevisiae, based on the System Dynamics approach, a general process-based model for two prokaryotic species of biotechnological interest, such as Escherichia coli and Bacillus subtilis, is proposed. The model is based on the main assumption that glycolytic intermediates act as central catabolic hub regulating the shift between respiratory and fermentative pathways. Furthermore, the description of a mixed fermentation with secondary by-products, characteristic of bacterial metabolism, is explicitly considered. The model also represents the inhibitory effect on growth and metabolism of self-produced toxic compounds relevant in assessing the late phases of high-cell density culture. Model simulations reproduced data from experiments reported in the literature with different strains of non-recombinant and recombinant E. coli and B. subtilis cultured in both batch and fed-batch reactors. The proposed model, based on simple biological assumptions, is able to describe the main dynamics of two microbial species of relevant biotechnological interest. It demonstrates that a reductionist System Dynamics approach to formulate simplified macro-kinetic models can provide a robust representation of cell growth and accumulation in the medium of fermentation by-products.

Eco-friendly Transformation of Waste Biomass to Biofuels

Background:

The development of viable alternative fuel sources is assuming a new urgency in the face of climate change and environmental degradation linked to the escalating consumption of fossil fuels. Lignocellulosic biomass is composed primarily of high-energy structural components such as cellulose, hemicellulose and lignin. The transformation of lignocellulosic biomass to biofuels requires the application of both pretreatment and conversion technologies.

Methods:

Several pretreatment technologies (e.g. physical, chemical and biological) are used to recover cellulose, hemicellulose and lignin from biomass and begin the transformation into biofuels. This paper reviews the thermochemical (e.g. pyrolysis, gasification and liquefaction), hydrothermal (e.g. subcritical and supercritical water gasification and hydrothermal liquefaction), and biological (e.g. fermentation) conversion pathways that are used to further transform biomass feedstocks into fuel products.

Results:

Through several thermochemical and biological conversion technologies, lignocellulosic biomass and other organic residues can produce biofuels such as bio-oils, biochar, syngas, biohydrogen, bioethanol and biobutanol, all of which have the potential to replace hydrocarbon-based fossil fuels.

Conclusions:

This review paper describes the conversion technologies used in the transformation of biomass into viable biofuels. Biofuels produced from lignocellulosic biomass and organic wastes are a promising potential clean energy source with the potential to be carbon-neutral or even carbonnegative.

Effect of sequential recycling of spent media wastewater on docosahexaenoic acid production by newly isolated strain Aurantiochytrium sp. ICTFD5

The main aim of this work was the optimization of recycled spent media wastewater (SMW) concentration for high biomass production of Aurantiochytrium sp. ICTFD5. Further, optimization for growth patterns and lipid accumulation capacity with three subsequent recycling runs was also performed. The biomass production after 96 h fermentation for recycling with 50% SMW was; 21.3 ± 1.5, 19.1 ± 1.3, 19 ± 1.2, and 23 ± 1.2 g/L for the first, second, third recycle runs, and control respectively. All the recycle runs were carried out with the same media and cultivation conditions. Subsequent recycling affected lipid accumulation, and it was decreased by ~4 to 9% compared to the control. The compositional shift of fatty acids was observed with sequential recycle runs, changing more towards saturated fatty acids content, suggesting it to be a new potential source for biodiesel feedstock.

Continuous Self-Cycling Fermentation Leads to Economical Lycopene Production by Saccharomyces cerevisiae

The economic feasibility and waste treatment problem are challenges to the industrialization of lycopene production from Saccharomyces cerevisiae. In this study, fermentation wastewater, biomass residue, and residual D-galactose are recycled for lycopene production. Results show that when fresh water is totally replaced by wastewater, lycopene titer attains 1.21 ± 0.02 g/L, which is 14.2% higher than the fresh water group (P < 0.05). An 80% replacement ratio of yeast extract by biomass residue causes no significant difference to lycopene production while 100% replacement ratio significantly lowers lycopene titer compared with the yeast extract group. Then, a novel fermentation medium containing wastewater and biomass residue with supplementing 3 g/L yeast extract and D-galactose is used for lycopene production. Lycopene titer increases 22.4% than the traditional fermentation in shake flasks (P < 0.05). Continuous self-cycling strategy using wastewater and biomass residue was tested in shake flasks. The mean lycopene titer of the first five recycles shows no significant difference with the start batch. Scaling up to 70 L fermenter, the mean lycopene titer attains 5.88 ± 0.15 g/L in three recycles, which is 22.25% higher than the start batch (P < 0.05). Economic analysis shows that the lowest unite product cost is achieved when four recycles are accomplished, which is 29.6% lower than the traditional fermentation while the chemical oxygen demand decreases 64.0%. Our study shows that continuous self-cycling fermentation process for lycopene production is feasible for the first time. The comprehensive utilization of wastewater and biomass residue from lycopene production by S. cerevisiae and achievement of high lycopene titer will hopefully accelerate industrialization of microbial production of lycopene.

Revisiting the Crabtree/Warburg effect in a dynamic perspective: a fitness advantage against sugar-induced cell death

The mechanisms behind the Warburg effect in mammalian cells, as well as for the similar Crabtree effect in the yeast Saccharomyces cerevisiae, are still a matter of debate: why do cells shift from the energy-efficient respiration to the energy-inefficient fermentation at high sugar concentration?

This review reports on the strong similarities of these phenomena in both cell types, discusses the current ideas, and provides a novel interpretation of their common functional mechanism in a dynamic perspective. This is achieved by analysing another phenomenon, the sugar-induced-cell-death (SICD) occurring in yeast at high sugar concentration, to highlight the link between ATP depletion and cell death.

The integration between SICD and the dynamic functioning of the glycolytic process, suggests that the Crabtree/Warburg effect may be interpreted as the avoidance of ATP depletion in those conditions where glucose uptake is higher than the downstream processing capability of the second phase of glycolysis. It follows that the down-regulation of respiration is strategic for cell survival allowing the allocation of more resources to the fermentation pathway, thus maintaining the cell energetic homeostasis.

Vegetable oils as carbon and energy source for Aureobasidium melanogenum in batch cultivation

Dark homogenous fungal‐based layers called biofinishes and vegetable oils are key ingredients of an innovative wood protecting system. The aim of this study was to determine which of the vegetable oils that have been used to generate biofinishes on wood will provide carbon and energy for the biofinish‐inhabiting fungus Aureobasidium melanogenum, and to determine the effect of the oil type and the amount of oil on the cell yield. Aureobasidium melanogenum was cultivated in shake flasks with different types and amounts of carbon‐based nutrients. Oil‐related total cell and colony‐forming unit growth were demonstrated in suspensions with initially 1% raw linseed, stand linseed, and olive oil. Oil‐related cell growth was also demonstrated with raw linseed oil, using an initial amount of 0.02% and an oil addition during cultivation. Nile red staining showed the accumulation of fatty acids inside cells grown in the presence of oil. In conclusion, each tested vegetable oil was used as carbon and energy source by A. melanogenum. The results indicated that stand linseed oil provides less carbon and energy than olive and raw linseed oil. This research is a fundamental step in unraveling the effects of vegetable oils on biofinish formation.

Accelerated Bioprocess Development of Endopolygalacturonase-Production with Saccharomyces cerevisiae Using Multivariate Prediction in a 48 Mini-Bioreactor Automated Platform

Mini-bioreactor systems enabling automatized operation of numerous parallel cultivations are a promising alternative to accelerate and optimize bioprocess development allowing for sophisticated cultivation experiments in high throughput. These include fed-batch and continuous cultivations with multiple options of process control and sample analysis which deliver valuable screening tools for industrial production. However, the model-based methods needed to operate these robotic facilities efficiently considering the complexity of biological processes are missing. We present an automated experiment facility that integrates online data handling, visualization and treatment using multivariate analysis approaches to design and operate dynamical experimental campaigns in up to 48 mini-bioreactors (8⁻12 mL) in parallel. In this study, the characterization of Saccharomyces cerevisiae AH22 secreting recombinant endopolygalacturonase is performed, running and comparing 16 experimental conditions in triplicate. Data-driven multivariate methods were developed to allow for fast, automated decision making as well as online predictive data analysis regarding endopolygalacturonase production. Using dynamic process information, a cultivation with abnormal behavior could be detected by principal component analysis as well as two clusters of similarly behaving cultivations, later classified according to the feeding rate. By decision tree analysis, cultivation conditions leading to an optimal recombinant product formation could be identified automatically. The developed method is easily adaptable to different strains and cultivation strategies, and suitable for automatized process development reducing the experimental times and costs.

Development of a method for the valorization of fermentation wastewater and algal-residue extract in docosahexaenoic acid production by Schizochytrium sp

Fermentation wastewater (FW) and algal residue are major by-products of docosahexaenoic acid (DHA) fermentations utilizing Schizochytrium sp. In order to reduce production costs and environmental pollution, we explored the application of FW and algal-residue extract (AE) for DHA production. Components analysis showed that FW and AE contained some mineral elements and protein residues, respectively. When they were used for DHA fermentation, results showed that 20% replacement of fresh water by FW and 80% replacement of yeast extract nitrogen by AE reached DHA content of 22.23 g/L and 27.10 g/L, respectively. Furthermore, a novel medium that utilizes a mixture of FW and AE was applied for DHA fermentation, whereby the final DHA yield reached 28.45 g/L, 24.56% higher than conventional medium. The strategy of valorizing fermentation waste provides a new method for reducing the costs and reducing environmental pollution of microbial fermentations.

Simultaneous saccharification and bioethanol production from corn cobs: Process optimization and kinetic studies

This study investigates the simultaneous saccharification and fermentation (SSF) process for bioethanol production from corn cobs with prehydrolysis (PSSF) and without prehydrolysis (OSSF). Two response surface models were developed with high coefficients of determination (>0.90). Process optimization gave high bioethanol concentrations and bioethanol conversions for the PSSF (36.92 ± 1.34 g/L and 62.36 ± 2.27%) and OSSF (35.04 ± 0.170 g/L and 58.13 ± 0.283%) models respectively. Additionally, the logistic and modified Gompertz models were used to study the kinetics of microbial cell growth and ethanol formation under microaerophilic and anaerobic conditions. Cell growth in the OSSF_{microaerophilic} process gave the highest maximum specific growth rate (µ_max) of 0.274 h^-1. The PSSF_{microaerophilic} bioprocess gave the highest potential maximum bioethanol concentration (P_m) (42.24 g/L). This study demonstrated that microaerophilic rather than anaerobic culture conditions enhanced cell growth and bioethanol production, and that additional prehydrolysis steps do not significantly impact on the bioethanol concentration and conversion in SSF process.

Functional Enzyme-Based Approach for Linking Microbial Community Functions with Biogeochemical Process Kinetics

The kinetics of biogeochemical processes in natural and engineered environmental systems is typically described using Monod-type or modified Monod-type models. These models rely on biomass as surrogates for functional enzymes in microbial communities that catalyze biogeochemical reactions. A major challenge of applying such models is the difficulty of quantitatively measuring functional biomass for the constraining and validation of the models. However, omics-based approaches have been increasingly used to characterize microbial community structure, functions, and metabolites. Here, we propose an enzyme-based model that can incorporate omics data to link microbial community functions with biogeochemical process kinetics. The model treats enzymes as time-variable catalysts for biogeochemical reactions and applies a biogeochemical reaction network to incorporate intermediate metabolites. The sequences of genes and proteins from metagenomes, as well as those from the UniProt database, were used for targeted enzyme quantification and to provide insights into the dynamic linkage among functional genes, enzymes, and metabolites that are required in the model. The application of the model was demonstrated using denitrification, as an example, by comparing model simulations with measured functional enzymes, genes, denitrification substrates, and intermediates.

Wastewater recycling technology for fermentation in polyunsaturated fatty acid production

To reduce fermentation-associated wastewater discharge and the cost of wastewater treatment, which further reduces the total cost of DHA and ARA production, this study first analyzed the composition of wastewater from Aurantiochytrium (DHA) and Mortierella alpina (ARA) fermentation, after which wastewater recycling technology for these fermentation processes was developed. No negative effects of DHA and ARA production were observed when the two fermentation wastewater methods were cross-recycled. DHA and ARA yields were significantly inhibited when the wastewater from the fermentation process was directly reused. In 5-L fed-batch fermentation experiments, using this cross-recycle technology, the DHA and ARA yields were 30.4 and 5.13gL^-1, respectively, with no significant changes (P>0.05) compared to the control group, and the water consumption was reduced by half compared to the traditional process. Therefore, this technology has great potential in industrial fermentation for polyunsaturated fatty acid production.

Engineering high-level production of fatty alcohols by Saccharomyces cerevisiae from lignocellulosic feedstocks

Fatty alcohols in the C12-C18 range are used in personal care products, lubricants, and potentially biofuels. These compounds can be produced from the fatty acid pathway by a fatty acid reductase (FAR), yet yields from the preferred industrial host Saccharomyces cerevisiae remain under 2% of the theoretical maximum from glucose. Here we improved titer and yield of fatty alcohols using an approach involving quantitative analysis of protein levels and metabolic flux, engineering enzyme level and localization, pull-push-block engineering of carbon flux, and cofactor balancing. We compared four heterologous FARs, finding highest activity and endoplasmic reticulum localization from a Mus musculus FAR. After screening an additional twenty-one single-gene edits, we identified increasing FAR expression; deleting competing reactions encoded by DGA1, HFD1, and ADH6; overexpressing a mutant acetyl-CoA carboxylase; limiting NADPH and carbon usage by the glutamate dehydrogenase encoded by GDH1; and overexpressing the Δ9-desaturase encoded by OLE1 as successful strategies to improve titer. Our final strain produced 1.2g/L fatty alcohols in shake flasks, and 6.0g/L in fed-batch fermentation, corresponding to ~ 20% of the maximum theoretical yield from glucose, the highest titers and yields reported to date in S. cerevisiae. We further demonstrate high-level production from lignocellulosic feedstocks derived from ionic-liquid treated switchgrass and sorghum, reaching 0.7g/L in shake flasks. Altogether, our work represents progress towards efficient and renewable microbial production of fatty acid-derived products.

Production of fatty acid-derived oleochemicals and biofuels by synthetic yeast cell factories

Sustainable production of oleochemicals requires establishment of cell factory platform strains. The yeast Saccharomyces cerevisiae is an attractive cell factory as new strains can be rapidly implemented into existing infrastructures such as bioethanol production plants. Here we show high-level production of free fatty acids (FFAs) in a yeast cell factory, and the production of alkanes and fatty alcohols from its descendants. The engineered strain produces up to 10.4 g l(-1) of FFAs, which is the highest reported titre to date. Furthermore, through screening of specific pathway enzymes, endogenous alcohol dehydrogenases and aldehyde reductases, we reconstruct efficient pathways for conversion of fatty acids to alkanes (0.8 mg l(-1)) and fatty alcohols (1.5 g l(-1)), to our knowledge the highest titres reported in S. cerevisiae. This should facilitate the construction of yeast cell factories for production of fatty acids derived products and even aldehyde-derived chemicals of high value.