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Abstract Consolidated bioprocessing (CBP) featuring concomitant hydrolysis of renewable substrates and microbial conversion into value-added biomolecules is considered to bring substantial benefits to the overall process efficiency. The biggest challenge in developing an economically feasible CBP process is identification of bifunctional biocatalyst merging the ability to utilize the substrate and convert it to value-added product with high efficiency. Yarrowia lipolytica is known for its exceptional performance in hydrophobic substrates assimilation and storage. On the other hand, its capacity to grow on plant-derived biomass is strongly limited. Still, its high potential to simultaneously overproduce several secretory proteins makes Y. lipolytica a platform of choice for expanding its substrate range to complex polysaccharides by engineering its hydrolytic secretome. This review provides an overview of different genetic engineering strategies advancing development of Y. lipolytica strains able to grow on the following four complex polysaccharides: starch, cellulose, xylan, and inulin. Much attention has been paid to genome mining studies uncovering native potential of this species to assimilate untypical sugars, as in many cases it turns out that dormant pathways are present in Y. lipolytica’s genome. In addition, the magnitude of the economic gain by CBP processing is here discussed and supported with adequate calculations based on simulated process models. Key points • The mini-review updates the knowledge on polysaccharide-utilizing Yarrowia lipolytica. • Insight into molecular bases founding new biochemical qualities is provided. • Model industrial processes were simulated and the associated costs were calculated.

Abstract Yarrowia lipolytica is a popular yeast species employed in multiple biotechnological production processes. High resistance to extreme environmental conditions or metabolic burden triggered by synthetically forced over-synthesis of a target metabolite has its practical consequences. The proud status of an “industrial workhorse” that Y. lipolytica has gained is directly related to such a quality of this species. With the increasing amount of knowledge coming from detailed functional studies and comprehensive omics analyses, it is now possible to start painting the landscape of the molecular background behind stress response and adaptation in Y. lipolytica. This review summarizes the current state-of-art of a global effort in revealing how Y. lipolytica responds to both environmental threats and the intrinsic burden caused by the overproduction of recombinant secretory proteins at the molecular level. Detailed lists of genes, proteins, molecules, and biological processes deregulated upon exposure to external stress factors or affected by over-synthesis of heterologous proteins are provided. Specificities and universalities of Y. lipolytica cellular response to different extrinsic and intrinsic threats are highlighted. Key points • Y. lipolytica as an industrial workhorse is subjected to multiple stress factors. • Cellular responses together with involved genes, proteins, and molecules are reviewed. • Native stress response mechanisms are studied and inspire engineering strategies.

Overproduction of recombinant secretory proteins triggers numerous physiological perturbations. Depending on a given heterologous protein characteristics, the producer cell is faced with different challenges which lead to varying responses in terms of its physiology and the target protein production rate. In the present study, we used steady-state-maintained Yarrowia lipolytica cells to investigate the impact of different heterologous proteins on the physiological behavior of the host cells. Such an approach allowed to uncouple the impact of the overproduction of a particular protein from the phenomena that result from growth phase or are caused by the heterogeneity of the analyzed populations. Altogether, eight variants of recombinant strains, individually overproducing heterologous proteins of varying molecular weight (27–65 kDa) and reporting activity (enzymatic and fluorescent) were subjected to chemostat cultivations. The steady-state-maintained cells were analyzed in terms of the substrate utilization, biomass and metabolites production, as well as the reporter protein synthesis. Simplified distribution of carbon and nitrogen between the respective products, as well as expression analysis of the heterologous genes were conducted. The here-obtained data suggest that using a more transcriptionally active promoter results in channeling more C flux towards the target protein, giving significantly higher specific amounts and production rates of the target polypeptide, at the cost of biomass accumulation, and with no significant impact on the polyols production. The extent of the reporter protein’s post-translational modifications, i.e., the number of disulfide bonds and glycosylation pattern, strongly impacts the synthesis process. Specific responses in terms of the protein formation kinetics, the gene expression levels, and transcript-to-protein linearity were observed.Key Points• Eight expression systems, producing different reporter proteins were analyzed.• The cells were maintained in steady-state by continuous chemostat culturing.• Protein- and promoter-specific effects were observed.

Current production of probiotic preparations must meet several criteria to be competitive on the market, like inexpensive growth medium based on sustainable resources, reduction of the number of unit operations, and exploitation of cost-effective preservation method. Implementation of the new solutions should not negatively affect the quality of the product, such as the number of living cells or the product safety. In the present study, we used a highly concentrated, raw corn flour-based (CF) medium for cultivation of probiotic L. plantarum LOCK 0860 strain and as a matrix in the following spray-drying process. Prior to drying, the post-culturing liquid was supplemented with a newly developed, optimized blend of protective agents, shown to increase the cell’s viability over 4-fold. Experimentally obtained data were used for the process model simulation at industrial scale, where the optimized probiotic component was supplemented with inulin as the prebiotic and standardization agent. Techno-economic analysis of this process model indicated a high net present value (NPV) at a selling price of $5.00 per kg of the preparation, which represent highly promising economic benefits. Sensitivity of unit production cost and the number of batches per year was estimated in the simulation, and the critical factors were identified, as well.

Abstract In this research, we were interested in answering a question whether subjecting a Yarrowia lipolytica strain overproducing a recombinant secretory protein (rs-Prot) to pre-optimized stress factors may enhance synthesis of the rs-Prot. Increased osmolarity (3 Osm kg−1) was the primary stress factor implemented alone or in combination with decreased temperature (20 °C), known to promote synthesis of rs-Prots. The treatments were executed in batch bioreactor cultures, and the cellular response was studied in terms of culture progression, gene expression and global proteomics, to get insight into molecular bases underlying an awaken reaction. Primarily, we observed that hyperosmolarity executed by high sorbitol concentration does not enhance synthesis of the rs-Prot but increases its transcription. Expectedly, hyperosmolarity induced synthesis of polyols at the expense of citric acid synthesis and growth, which was severely limited. A number of stress-related proteins were upregulated, including heat-shock proteins (HSPs) and aldo–keto reductases, as observed at transcriptomics and proteomics levels. Concerted downregulation of central carbon metabolism, including glycolysis, tricarboxylic acid cycle and fatty acid synthesis, highlighted redirection of carbon fluxes. Elevated abundance of HSPs and osmolytes did not outbalance the severe limitation of protein synthesis, marked by orchestrated downregulation of translation (elongation factors, several aa-tRNA synthetases), amino acid biosynthesis and ribosome biogenesis in response to the hyperosmolarity. Altogether we settled that increased osmolarity is not beneficial for rs-Prots synthesis in Y. lipolytica, even though some elements of the response could assist this process. Insight into global changes in the yeast proteome under the treatments is provided. Key points • Temp enhances, but Osm decreases rs-Prots synthesis by Y. lipolytica. • Enhanced abundance of HSPs and osmolytes is overweighted by limited translation. • Global proteome under Osm, Temp and Osm Temp treatments was studied.

Yeasts comprise a divergent group of microorganisms playing an important role in foods production. To monitor the production processes, validate authenticity and safety of foods, reliable methods of yeast identification and differentiation are needed. Nowadays, traditional PCR/sequencing-based methods are replaced by rapid techniques not requiring post-PCR processing. In the present study, we developed a three region-based qPCR-HRM protocol, for rapid differentiation of yeast species isolated from food products. The three targeted fragments (26S rDNA, 18S rDNA, ITS) were carefully analyzed to dock the primers at inter-species conservative regions, flanking polymorphic regions of ∼200 bp. Thirty eight yeast strains were used as a training material. The collection of yeast spanned Pichia, Clavispora, Candida, Yarrowia, Kluyveromyces, Saccharomyces, and Wickerhamomyces genera. MALDI-TOF mass spectrometry and conventional rDNA sequencing were used for validation. Conducted studies demonstrated that when used individually, each of the three regions analyzed by qPCR-HRM possessed its own yeast species-specific limitations, sometimes leading to inaccurate taxonomic classification. On the other hand, simultaneous analysis of the three proposed regions resulted in rapid and adequate differentiation of all the yeast strains at species-level resolution.

DNA methylation is a common, but not universal, epigenetic modification that plays an important role in multiple cellular processes. While definitely settled for numerous plant, mammalian, and bacterial species, the genome methylation in different fungal species, including widely studied and industrially-relevant yeast species, Yarrowia lipolytica, is still a matter of debate. In this paper, we report a differential DNA methylation level in the genome of Y. lipolytica subjected to sequential subculturing and to heat stress conditions. To this end, we adopted repeated batch bioreactor cultivations of Y. lipolytica subjected to thermal stress in specific time intervals. To analyze the variation in DNA methylation between stressed and control cultures, we (a) quantified the global DNA methylation status using an immuno-assay, and (b) studied DNA methylation patterns through whole-genome sequencing. Primarily, we demonstrated that 5 mC modification can be detected using a commercial immuno-assay, and that the modifications are present in Y. lipolytica’s genome at ~0.5% 5 mC frequency. On the other hand, we did not observe any changes in the epigenetic response of Y. lipolytica to heat shock (HS) treatment. Interestingly, we identified a general phenomenon of decreased 5 mC level in Y. lipolytica’s genome in the stationary phase of growth, when compared to a late-exponential epigenome. While this study provides an insight into the subculturing stress response and adaptation to the stress at epigenetic level by Y. lipolytica, it also leaves an open question of inability to detect any genomic DNA methylation level (either in CpG context or context-less) through whole-genome sequencing. The results of ONT sequencing, suggesting that 5 mC modification is either rare or non-existent in Y. lipolytica genome, are contradicted with the results of the immunoassay.

Fed-batch cultivation is the preferred bioprocessing strategy applied in microbial production of proteins. Feeding strategy is crucial parameters to be optimized upon development of a fed-batch process. In this study, we investigated impact of different feeding strategies on production of recombinant enzymatic protein in Yarrowia lipolytica cultures. From amongst tested strategies, comprising intermittent and continuous feedings, also in cascade with respiratory factors, intermittent feeding executed after complete exhaustion of glycerol from the medium, with moderate amplitude of osmolarity, was the most beneficial in terms of the secretory enzyme amount, its volumetric productivity and specific activity. Because adopted feeding strategies strongly modulated osmolarity of the cultures, the effect of osmotic pressure on production of the target heterologous protein was investigated in a series of batch cultivations with addition of osmoactive compounds (NaCl, sorbitol, sucrose, and glycerol) at different concentrations. Although obvious promoting effect of the osmoactive substances on the enzyme production was clear, no straightforward correlation between the medium osmolarity and the target enzyme's specific activity could be observed. These results suggest that not only the level of osmolarity but also chemical character of the osmoactive compound have both important impact on the production of secretory proteins in Y. lipolytica cultures.

In order to assess the essential probiotic properties of a strain dedicated for administration in humans and animals, characteristics of finally formulated products, rather than the cells solely, seems to be of crucial importance. In this study, composition of protective blends for manufacture of L. lactis probiotic powders was optimized using a statistical experimental design. The powders, generated by either spray- or freeze-drying techniques, were subsequently subjected to storage testing, and in vitro digestion in simulated stomach and small intestine. Finally, maintenance of adherence capability to human enterocyte-like cell lines, was evaluated. Our data demonstrated that 10% trehalose ensures the highest viability of L. lactis bacteria upon both drying techniques (viability of 60–68%). Moreover, skimmed milk-protected spray-dried cells exhibit the highest resistance to harsh environmental conditions of stomach (53.9 ± 7.6% survival rate) and higher adhesion ability to HT-29 cell line after digestion (528 ± 29 cells per 100 epithelial cells).

High-throughput function-based screening techniques remain the major bottleneck in the novel biocatalysts development pipeline. In the present study, we customized protocols for amylolytic activity determination (Somogyi-Nelson and starch-iodine tests) to micro-volume thermalcycler-based assays (linearity range 60–600 μM of reducing sugar, R2 = 0.9855; 0–2 mg/mL of starch, R2 = 0.9921, respectively). Exploitation of a thermalcycler enabled rapid and accurate temperature control, further reduction of reagents and samples volumes, and limited evaporation of the reaction mixtures, meeting several crucial requirements of an adequate enzymatic assay. In the optimized micro-volume Somogyi-Nelson protocol, we were able to reduce the time required for high-temperature heating sixfold (down to 5 min) and further increase sensitivity of the assay (tenfold), when compared to the previous MTP-based protocol. The optimized microassays have complementary scope of specificities: micro-starch-iodine test for endoglucanases, micro-Somogyi-Nelson test for exoglucanases. Due to rapid, micro-volume and high-throughput character, the methods can complement toolbox assisting development of novel biocatalysts and analysis of saccharides-containing samples. Electronic supplementary material The online version of this article (10.1007/s00253-018-09610-0) contains supplementary material, which is available to authorized users.

Accurate quantitation of gene expression levels require sensitive, precise and reproducible measurements of specific transcripts. Normalization to a reference gene is the most common practice to minimize the impact of the uncontrolled variation. The fundamental prerequisite for an accurate reference gene is to be stably expressed amongst all the samples included in the analysis. In the present study we aimed to assess the expression level and stability of a panel of 21 genes in Yarrowia lipolytica throughout varying conditions, covering composition of the culturing medium, growth phase and strain—wild type and recombinant burdened with heterologous protein overexpression. The panel of the selected candidate genes covered those essential for growth and maintenance of metabolism and homologs of commonly used internal references in RT-qPCR. The candidate genes expression level and stability were assessed and the data were processed using dedicated computational tools (geNorm and NormFinder). The results obtained here indicated genes unaffected by the burden of overexpression (TEF1, TPI1, UBC2, SRPN2, ALG9-like, RYL1) or by the culture medium used (ACT1, TPI1, UBC2, SEC61, ODC, CLA4, FKS1, TPS1), as well as those the least (SSDH, ODC, GPD) and the most (SEC62, TPI1, IPP1) suitable for normalization of RT-qPCR data in Y. lipolytica.

Sustainable economy drives increasing demand for raw biomass-decomposing enzymes. Microbial expression platforms exploited as cellular factories of such biocatalysts meet requirements of large-volume production. Previously, we developed Yarrowia lipolytica recombinant strains able to grow on raw starch of different plant origin. In the present study, we used the most efficient amylolytic strain as a microbial cell factory of raw-starch-digesting (RSD) amylolytic preparation composed of two enzymes. The RSD-preparation was produced in fed-batch bioreactor cultures. Concentrated and partly purified preparation was then tested in simultaneous saccharification and fermentation (SSF) processes with thermotolerant Kluyveromyces marxianus for ethanol production and Lactobacillus plantarum for production of lactic acid. These processes were conducted as a proof-of-concept that application of the novel RSD-preparation supports sufficient starch hydrolysis enabling microbial growth and production of targeted molecules, as the selected strains were confirmed to lack amylolytic activity. Doses of the preparation and thermal conditions were individually adjusted for the two processes. Additionally, ethanol production was tested under different aeration strategies, and lactic acid production process was tested in thermally pre-treated substrate, as well. Conducted studies demonstrated that the novel RSD-preparation provides satisfactory starch hydrolyzing activity for ethanol and lactic acid production from starch by non-amylolytic microorganisms.

Abstract Nowadays considerable effort is being pursued towards development of consolidated microbial biocatalysts that will be able to utilize complex, non-pretreated substrates and produce valuable compounds. In such engineered microbes, synthesis of extracellular hydrolases may be fine-tuned by different approaches, like strength of promoter, type of secretory tag, and gene copy number. In this study, we investigated if organization of a multi-element expression cassette impacts the resultant Yarrowia lipolytica transformants’ phenotype, presuming that different variants of the cassette are composed of the same regulatory elements and encode the same mature proteins. To this end, Y. lipolytica cells were transformed with expression cassettes bearing a pair of genes encoding exactly the same mature amylases, but fused to four different signal peptides (SP), and located interchangeably in either first or second position of a synthetic DNA construction. The resultant strains were tested for growth on raw and pretreated complex substrates of different plant origin for comprehensive examination of the strains’ acquired characteristics. Optimized strain was tested in batch bioreactor cultivations for growth and lipids accumulation. Based on the conducted research, we concluded that the positional order of transcription units (TU) and the type of exploited SP affect final characteristics of the resultant consolidated biocatalyst strains, and thus could be considered as additional factors to be evaluated upon consolidated biocatalysts optimization. Key Points • Y. lipolytica growing on raw starch was constructed and tested on different substrates. • Impact of expression cassette design and SP on biocatalysts’ phenotype was evidenced. • Consolidated biocatalyst process for lipids production from starch was conducted.

Industrially relevant traits of Yarrowia lipolytica, like high growth rate, capacity to grow at high cell density or to synthesize biomolecules with high productivities, strongly rely on sufficient oxygen provision. Although the impact of oxygen availability (OA) on the physiology of Y. lipolytica has been already studied, its influence on recombinant protein (rProt) synthesis and secretion has been largely neglected to date. With the aim to fill this gap, a fluorescent reporter protein (yellow fluorescent protein [YFP]) was used herein as a proxy to follow simultaneously rProt synthesis and secretion in Y. lipolytica under different OAs. This study covers the analysis of the reporter gene expression through reverse transcription quantitative polymerase chain reaction, polypeptide synthesis and its retention-to-secretion ratio using flow cytometry and fluorymetry during shake flasks and bioreactor cultivations under different OA. The results gathered demonstrate that OA has a dramatic impact on the kinetics of intracellular and extracellular YFP accumulation. Higher rProt production and secretion were favoured under high OA, and were largely related to OA and not to cell growth. Our observations also suggest the existence of some upper limit of secretory protein accumulation inside the cells above which massive secretion is initiated. Moreover, at low OA, the first bottleneck in rProt synthesis occurs as early as at transcription level, which could results from a lower availability of transcriptional machinery elements. Finally, using flow cytometry and bioreactor cultivations, we highlighted that ovoid cells are generally more efficient in terms of rProt synthesis.

Depending on the suboptimal factor, the target protein secretion can be over 1000-fold below the theoretical maximum. The bottlenecks may be alleviated by co-overexpression of “secretory helpers” (SHs). Here we proposed twelve SHs, functionally spanning the whole transcription-translation-translocation-folding-maturation-excretion pipeline. The genes were co-transformed with an easy-to-track reporter, and tested less than two temperatures. Our results indicated a clear distinction in the effects triggered by SHs involved in either synthesis or trafficking of the heterologous polypeptides. For superior operation of synthesis-related SHs, namely RPL3, SSA5 and SSA8, the secretory pathway's capacity must be released by applying decreased temperature (25 °C). The other SHs considered (e.g. SSO1, CWP11) did not give such spectacular results in the amounts of the target heterologous polypeptide, but allowed to maintain secretory capacity under unfavorable thermal conditions. This study provides generalizable guidelines for cloning/culturing strategies aiming at enhancement of heterologous protein secretion in Y. lipolytica.

Recently we reported on raw-starch-digesting ability of alpha-amylase from an insect Sitophilus oryzae (SoAMY) expressed in recombinant Yarrowia lipolytica cells, and demonstrated its usefulness in simultaneous saccharification and fermentation processes with industrial yeasts. In this study we applied fed-batch cultures of Y. lipolytica 4.29 strain reaching high-cell-densities (up to 70 [gDCW/L]), to enhance SoAMY production. SoAMY activity in the medium reached the peak value of 22,979.23 ± 184 [AU/L], at volumetric productivity of 121.58 ± 1.75 [AU/L/h], and yield of 71.83 ± 3.08 [AU/gglycerol], constituting roughly 160-fold improvement, compared to the best previous result. The cultivations were accompanied by high production of erythritol (83.58 [g/L]), at the marginal production of mannitol (5.46 [g/L]). Elementary analyses of media constituents, the enzyme and the yeast biomass gave better insight into carbon and nitrogen fluxes distribution. Due to application of genetic engineering and bioprocess engineering strategies, the insect-derived enzyme can be produced at the quantities competitive to microbial catalysts.

Yarrowia lipolytica has emerged as an alternative expression system for heterologous protein production and enzyme evolution. Several different expression systems dedicated for this species have been developed, ranging from the simple cloning of expression vectors to recently developed high-throughput methodologies using efficient cloning and assembly such as Gateway and Golden Gate strategies. The latter strategies, due to their modular character, enable multiple vector construction and the construction of expression cassettes containing different genes or a gene under different promoters of various strengths.Here, we present the Golden Gate cloning strategy for the construction of multiple expression cassettes, the transformation into Y. lipolytica, and the selection of efficient enzyme-producing strains using an insect alpha-amylase as a reporter detected via a thermal cycler-based microassay.

International audience; The non-conventional model yeast Yarrowia lipolytica is of increasing interest as a cell factory for producing recombinant proteins or biomolecules with biotechnological or pharmaceutical applications. To further develop the yeast's efficiency and construct inducible promoters, it is crucial to better understand and engineer promoter architecture. Four conserved cis-regulatory modules (CRMs) were identified via phylogenetic footprinting within the promoter regions of EYD1 and EYK1, two genes that have recently been shown to be involved in erythritol catabolism. Using CRM mutagenesis and hybrid promoter construction, we identified four upstream activation sequences (UASs) that are involved in promoter induction by erythritol. Using RedStarII fluorescence as a reporter, the strength of the promoters and the degree of erythritol-based inducibility were determined in two genetic backgrounds: the EYK1 wild type and the eyk1 mutant. We successfully developed inducible promoters with variable strengths, which ranged from 0.1 SFU/h to 457.5 SFU/h. Erythritol-based induction increased 2.2 to 32.3 fold in the EYK1+wild type and 2.9 to 896.1 fold in the eyk1 mutant. This set of erythritol-inducible hybrid promoters could allow the modulation and fine-tuning of gene expression levels. These promoters have direct applications in protein production, metabolic engineering and synthetic biology. This study identified cis-regulatory modules (CRMs) for the EYK1 and EYD1 promoters in Yarrowia lipolytica, which allowed the development of erythritol-inducible hybrid promoters with practical applications in metabolic engineering and synthetic biology.

International audience; Microbial production of secretory proteins constitutes one of the key branches of current industrial biotechnology, earning billion dollar (USD) revenues each year. That industrial branch strongly relies on fluent operation of the secretory machinery within a microbial cell. The secretory machinery, directing the nascent polypeptide to its final destination, constitutes a highly complex system located across the eukaryotic cell. Numerous molecular identities of diverse structure and function not only build the advanced network assisting folding, maturation and secretion of polypeptides but also serve as sensors and effectors of quality control points. All these events must be harmoniously orchestrated to enable fluent processing of the protein traffic. Availability of these elements is considered to be the limiting factor determining capacity of protein traffic, which is of crucial importance upon biotechnological production of secretory proteins. The main purpose of this work is to review and discuss findings concerning secretory machinery operating in a non-conventional yeast species, Yarrowia lipolytica, and to highlight peculiarities of this system prompting its use as the production host. The reviewed literature supports the thesis that secretory machinery in Y. lipolytica is characterized by significantly higher complexity than a canonical yeast protein secretion pathway, making it more similar to filamentous fungi-like systems in this regard.

PMID: 30737739 Chapter 6; International audience; Yarrowia lipolytica has emerged as an alternative expression system for heterologous protein production and enzyme evolution. Several different expression systems dedicated for this species have been developed, ranging from the simple cloning of expression vectors to recently developed high-throughput methodologies using efficient cloning and assembly such as Gateway and Golden Gate strategies. The latter strategies, due to their modular character, enable multiple vector construction and the construction of expression cassettes containing different genes or a gene under different promoters of various strengths.Here, we present the Golden Gate cloning strategy for the construction of multiple expression cassettes, the transformation into Y. lipolytica, and the selection of efficient enzyme-producing strains using an insect alpha-amylase as a reporter detected via a thermal cycler-based microassay.

In view of the constantly increasing demand for cost-effective, low-energy and environmentally friendly industrial processes and household care products, enzyme production occupies an essential place in the field of biotechnology. Along with increasing demand for industrial and household care enzymes, the demand for heterologous expression platforms has also increased. Apart from the conventional hosts, e.g. Escherichia coli, Saccharomyces cerevisiae and Pichia pastoris, routinely used in heterologous protein expression, the non-conventional ones have become more and more exploited in this field. Among the available yeast host systems, Yarrowia lipolytica appears to be an attractive alternative. The aim of this study was to compare efficiency of two Yarrowia-based expression platforms, commercial Po1g–pYLSC and custom-made A18-pYLTEF, in expression of an insect-derived, raw-starch-digesting α-amylase, to select the ‘champion’ system for further studies on this valuable enzyme. Both expression platforms were compared with respect to copy number of the integrated expression cassette/transformed genome, and the recombinant strains performance (Po1g–pYLSC-derived 4.29 strain, and A18-pYLTEF-derived B9 strain) during batch bioreactor cultures. Our results demonstrate that the average number of integration events into the recipient's genome was comparable for both expression systems under investigation, but with varying distribution of the multicopy integrants; and the number of the recombinant gene copies was highly correlated with the acquired amylolytic activity of the strains. Due to severe susceptibility of the recombinant AMY1 polypeptide to native proteases of the custom-made expression system, the final yield of the enzyme was substantially lower when compared to the commercial Po1g–pYLSC (reaching a maximum level of 142.84 AU/l). Copyright © 2015 John Wiley & Sons, Ltd.

In this study, the scale-up of erythritol production from glycerol using the Yarrowia lipolytica strain MK1 is proposed. The experiments included increasing the scale from laboratory (VW = 0.002 m3) to pilot plant (VP = 0.5 m3). Only slight differences in the erythritol production rate were observed between the two culture variants. Erythritol concentration in the pilot plant experiment reached 180.3 kg/m3, with productivity 1.25 kg/m3·h and yield 0.533 kg/kg of the total amount of glycerol consumed. A model of an industrial installation for production of erythritol crystals, with the production rate of 1075 MT (Metric tone)/year, based on data derived from experimental work, was developed in SuperPro Designer V9.5 software. The potential of SuperPro Designer software was demonstrated in the framework of detailed analyses of cost-effectiveness and sensitivity for the production process. The industrial application of erythritol production from yeast is strongly dependent on the glycerol price and on the fermentation time. The process is based on cheap raw material, is fully scalable, and the collected data can serve as a basis for development of a production model. To our knowledge, this is the first report about scale-up of microbial erythritol production from glycerol and combined with the fact that the remaining biomass may be used as animal feed, makes the whole technology waste-free and economically viable.

Upon expression of a given protein in an expression host, its secretion into the culture medium or cell-surface display is frequently advantageous in both research and industrial contexts. Hence, engineering strategies targeting folding, trafficking, and secretion of the proteins gain considerable interest. Yarrowia lipolytica has emerged as an efficient protein expression platform, repeatedly proved to be a competitive secretor of proteins. Although the key role of signal peptides (SPs) in secretory overexpression of proteins and their direct effect on the final protein titers are widely known, the number of reports on manipulation with SPs in Y. lipolytica is rather scattered. In this study, we assessed the potential of ten different SPs for secretion of two heterologous proteins in Y. lipolytica. Genomic and transcriptomic data mining allowed us to select five novel, previously undescribed SPs for recombinant protein secretion in Y. lipolytica. Their secretory potential was assessed in comparison with known, widely exploited SPs. We took advantage of Golden Gate approach, for construction of expression cassettes, and micro-volume enzymatic assays, for functional screening of large libraries of recombinant strains. Based on the adopted strategy, we identified novel secretory tags, characterized their secretory capacity, indicated the most potent SPs, and suggested a consensus sequence of a potentially robust synthetic SP to expand the molecular toolbox for engineering Y. lipolytica. Electronic supplementary material The online version of this article (10.1007/s00253-018-8966-9) contains supplementary material, which is available to authorized users.

Starch is the dominant feedstock consumed for the bioethanol production, accounting for 60 % of its global production. Considering the significant contribution of bioethanol to the global fuel market, any improvement in its major operating technologies is economically very attractive. It was estimated that up to 40 % of the final ethanol unit price is derived from the energy input required for the substrate pre-treatment. Application of raw starch hydrolyzing enzymes (RSHE), combined with operation of the process according to a simultaneous saccharification and fermentation (SSF) strategy, constitutes the most promising solutions to the current technologies limitations. In this study, we expressed the novel RSHE derived from an insect in Saccharomyces cerevisiae strain dedicated for the protein overexpression. Afterwards, the enzyme performance was assessed in SSF process conducted by industrial ethanologenic or thermotolerant yeast species. Comparison of the insect-derived RSHE preparation with commercially available amylolytic RSH preparation was conducted. Our results demonstrate that the recombinant alpha-amylase from rice weevil can be efficiently expressed and secreted with its native signal peptide in S. cerevisiae INVSc-pYES2-Amy1 expression system (accounting for nearly 72 % of the strain's secretome). Application of the recombinant enzyme-based preparation in SSF process secured sufficient amylolytic activity for the yeast cell propagation and ethanol formation from raw starch. (Oligo)saccharide profiles generated by the compared preparations differed with respect to homogeneity of the sugar mixtures. Concomitantly, as demonstrated by a kinetic model developed in this study, the kinetic parameters describing activity of the compared preparations were different.

In this study, the isolated strain, Citrobacter freundii AD970, was genetically modified to improve production of 1,3-propanediol (1,3-PD). The strain was modified through overexpression of 1,3-PD oxidoreductase (PDOR from Shimwellia blattae), catalyzing the final step of glycerol-to-1,3-PD conversion. The aim of such approach was to decrease accumulation of toxic 3-hydroxypropionaldehyde (3-HPA) and to increase 1,3-PD synthesis. To this end, a genetic construct suitable for the modification of the strain was developed. Our results showed that PDOR was successfully overexpressed in the novel expression system. Flask cultivations in a glycerol-based medium demonstrated that the modified strain produced nearly two-fold higher concentrations of 1,3-PD (8.6 vs. 4.75 g/L). During bioreactor fed-batch cultivations in a glycerol-based medium, accumulation of 3-HPA was successfully decreased, leading to enhanced 1,3-PD synthesis (35.6 vs. 25.5 g/L), at higher yield (0.49 vs. 0.44 mol/mol at 48 h) and productivity (12.41 vs. 8.06 g1,3-PD/gDCW and 0.32 vs. 0.23 g1,3-PD/(L*h)). Considering the final volume of the fed-batch cultures, the V + I strain synthesized 20 g more of 1,3-PD (49.9 g vs. 29.9 g). To the best of our knowledge, this is the first report on genetic engineering of a wild-type Citrobacter strain to modulate the 1,3-PD synthesis pathway.

Raw-starch-digesting enzymes (RSDE) are of major importance for industrial applications, as their usage greatly simplifies the starch processing pipeline. To date, only microbial RSDE have gained considerable attention, since only microbial production of enzymes meets industrial demands. In this study, α-amylase from rice weevil (Sitophilus oryzae), the major rice pest, was cloned and expressed in Yarrowia lipolytica Po1g strain. The enzyme was secreted into the culture medium, and the peak activity (81 AU/L) was reached after only 29 h of culturing in 5-L bioreactors. Through simple purification procedure of ammonium sulfate precipitation and affinity chromatography, it was possible to purify the enzyme to apparent homogeneity (25-fold purification factor, at 5 % yield). The optimal conditions for the α-amylase activity were pH 5.0 and a temperature of 40 °C. The α-amylase studied here did not show any obligate requirement for Ca(2+) ions. The recombinant α-amylase appeared to efficiently digest granular starch from pea, amaranth, waxy corn, and waxy rice.

International audience; The increasing market demands of β-carotene as colorant, antioxidant and vitamin precursor, requires novel biotechnological production platforms. Yarrowia lipolytica, is an industrial organism unable to naturally synthesize carotenoids but with the ability to produce high amounts of the precursor Acetyl-CoA. We first found that a lipid overproducer strain was capable of producing more β-carotene than a wild type after expressing the heterologous pathway. Thereafter, we developed a combinatorial synthetic biology approach base on Golden Gate DNA assembly to screen the optimum promoter-gene pairs for each transcriptional unit expressed. The best strain reached a production titer of 1.5 g/L and a maximum yield of 0.048 g/g of glucose in flask. β-carotene production was further increased in controlled conditions using a fed-batch fermentation. A total production of β-carotene of 6.5 g/L and 90 mg/g DCW with a concomitant production of 42.6 g/L of lipids was achieved. Such high titers suggest that engineered Y. lipolytica is a competitive producer organism of β-carotene.

Summary In this study, we have adopted Golden Gate modular cloning strategy to develop a robust and versatile DNA assembly platform for the nonconventional yeast Yarrowia lipolytica. To this end, a broad set of destination vectors and interchangeable building blocks have been constructed. The DNA modules were assembled on a scaffold of predesigned 4 nt overhangs covering three transcription units (each bearing promoter, gene and terminator), selection marker gene and genomic integration targeting sequences, constituting altogether thirteen elements. Previously validated DNA modules (regulatory elements and selection markers) were adopted as the Golden Gate bricks. The system's operability was demonstrated based on synthetic pathway of carotenoid production. This technology greatly enriches a molecular biology toolbox dedicated to this industrially relevant microorganism enabling fast combinatorial cloning of complex synthetic pathways.

Cross-flow microfiltration of fermented mash containing native corn starch granules from a simultaneous saccharification and fermentation process, was investigated with respect to the process performance. Influence of transmembrane pressure and cross-flow velocity on normalized permeate flux rate decline and membrane fouling were examined. The microfiltration system was equipped with a tubular ceramic membrane with 0.45 μm pore size. A combined pore-blockage–cake-filtration model was successfully used to determine the process performance and identify principal fouling mechanisms. Experimental results revealed that the fouling phenomenon taking place during microfiltration of the fermented mash follows a pattern of initial complete pore blockage and subsequent cake formation. As a result, initial rapid flux decline is followed by gradual flux decline. Fouled membranes were characterized using scanning electron microscopy (SEM). The membrane surface characteristics examined by SEM images evidenced formation of dense deposit on the upper membrane surface. Rinsing the fouled membrane with water followed by investigation of the permeate flux rate indicated occurrence of increased fouling, when microfiltration was carried out at high transmembrane pressure. The highest normalized flux decline was observed for microfiltration operated at the highest transmembrane pressure (1.4 bar) and the lowest cross flow velocity (1 m s−1). It is recommended to use high cross-flow velocity (4.55 m s−1) and low transmembrane pressure (0.35 bar) to minimize membrane fouling, triggered by components of the fermented mash.

Our previous studies showed that glycerol fermentation by Hafnia alvei AD27 strain was accompanied by formation of high quantities of lactate. The ultimate aim of this work was the elimination of excessive lactate production in the 1,3-propanediol producer cultures. Group II intron-mediated deletion of ldh (lactate dehydrogenase) gene in an environmental isolate of H. alvei AD27 strain was conducted. The effect of the Δldh genotype in H. alvei AD27 strain varied depending on the culture medium applied. Under lower initial glycerol concentration (20 gL-1), lactate and 1,3-propanediol production was fully abolished, and the main carbon flux was directed to ethanol synthesis. On the other hand, at higher initial glycerol concentrations (40 gL-1), 1,3-propanediol and lactate production was recovered in the recombinant strain. The final titers of 1,3-propanediol and ethanol were similar for the recombinant and the WT strains, while the Δldh genotype displayed significantly decreased lactate titer. The by-products profile was altered upon ldh gene deletion, while glycerol utilization and biomass accumulation remained unaltered. As indicated by flow-cytometry analyses, the internal pH was not different for the WT and the recombinant Δldh strains over the culture duration, however, the WT strain was characterized by higher redox potential.

1,3-Propanediol (1,3-PD) production by fermentation of glycerol was first described in 1881 but little attention was paid to this biosynthesis for over a century. An increasing interest in microbial 1,3-PD production is observed since late 1980s. The high growth rate of the biofuel market and the perspective of glycerol becoming abundant attract even more attention to this valuable chemical. Glycerol conversion to 1,3-PD is known to occur in Clostridia, Enterobacteriaceae and Lactobacillaceae. Some clostridial species are among the best 1,3-PD producers. This work is a review of the current state of research on Clostridium spp. strains that ferment glycerol to 1,3-PD. It focuses on the metabolic pathways and factors that influence the production of this diol. The effects of different environmental stresses on the process of 1,3-PD synthesis are also covered. Moreover, various genetic engineering methods utilized in order to improve the capabilities of bacteria used in this process are presented.

Klebsiella spp are one of the best natural producers of 1,3-propanediol (1,3-PD). However, their usage in the biotechnological production of the diol is limited, since the species belong to the second hazard group. Nevertheless, multiple advantageous traits of Klebsiella spp justify the international effort devoted to develop a biotechnological process of 1,3-PD production with these microorganisms. Apart from the process engineering approach aiming at improvement of 1,3-PD production by Klebsiella spp, plethora of metabolic engineering approaches have been reported. Different strategies have been undertaken to genetically improve Klebsiella strains and provide them with the ability to synthesize 1,3-PD more efficiently. These include over-expression of both homologous and heterologous genes of the 1,3-PD synthesis pathway, protein and cofactor engineering, deletion of the genes involved in by-products formation. This review provides an overview of the initial and most recent reports on the metabolic engineering of Klebsiella spp with the aim of improvement of 1,3-PD biosynthesis.

The history of 1,3-propanediol (1,3-PD) conversion from being a specialty chemical to being a bulk chemical illustrates that the concerted effort of different metabolic engineering approaches brings the most successful results. In order to metabolically tailor the 1,3-PD production pathway multiple strategies have been pursued. Knocking-out genes responsible for by-products formation, intergeneric transfer and overexpression of the genes directly involved in the pathway, manipulation with internal redox balance, introduction of a synthetic flux control point, and modification of the substrate mechanism of transport are some of the strategies applied. The metabolic engineering of the microbial 1,3-PD production exploits both native producers and microorganisms with acquired ability to produce the diol via genetic manipulations. Combination of the appropriate genes from homologous and heterologous hosts is expected to bring a desired objective of production of 1,3-PD cheaply, efficiently and independently from non-renewable resources. The state-of-the-art of the 1,3-PD pathway metabolic engineering is reviewed in this paper.

The pivotal role of non-conventional yeast (NCY) species in formation of valuable aroma compounds in various food commodities is widely acknowledged. This fact inspires endeavors aiming at exploitation of food-derived NCYs as biocatalysts in natural aromas production. In this study, we isolated, characterized and evaluated aroma-producing capacity of two NCY representatives—Pichia cactophila 7.20 and Klyuveromyces lactis 6.10 strains. The strains were isolated from food-related habitats—goat-milk regional cheese and Swiss-type ripening cheese, respectively. Aroma profiles generated by the two strains cultured in a general rich medium were analyzed through solvent extraction and GC-MS analysis of the compounds retained in the culture media. Finally, the strains were tested in bioconversion cultures with branched chain- or aromatic amino acids as the sole nitrogen source, to assess capability of the strains towards formation of amino acid-derived aromas. The results showed extraordinary capacity of both strains for production of 2-phenylethanol (at more than 3 g/L) and isoamyl alcohol (approx. 1.5 g/L). A distinctive trait of 2-phenylethyl acetate synthesis at high concentrations (0.64 g/L) was revealed for P. cactophila 7.20 strain. Highly valued disulfide dimethyl as well as methionol acetate were identified amongst the aroma compounds synthesized by the strains.

Biotechnological production of 2,3-butanediol (hereafter referred to as 2,3-BD) from wastes and excessive biomass is a promising and attractive alternative for traditional chemical synthesis. In the face of scarcity of fossil fuel supplies the bio-based process is receiving a significant interest, since 2,3-BD may have multiple practical applications (e.g. production of synthetic rubber, plasticizers, fumigants, as an antifreeze agent, fuel additive, octane booster, and many others). Although the 2,3-BD pathway is well known, microorganisms able to ferment biomass to 2,3-BD have been isolated and described, and attempts of pilot scale production of this compound were made, still much has to be done in order to achieve desired profitability. This review summarizes hitherto gained knowledge and experience in biotechnological production of 2,3-BD, sources of biomass used, employed microorganisms both wild type and genetically improved strains, as well as operating conditions applied.

Background High supply of raw, residual glycerol from biodiesel production plants promote the search for novel biotechnological methods of its utilization. In this study we attempted modification of glycerol catabolism in a nonconventional yeast species Yarrowia lipolytica through genetic engineering approach. Results To address this, we developed a novel genetic construct which allows transferring three heterologous genes, encoding glycerol dehydratase, its reactivator and a wide-spectrum alcohol oxidoreductase under the control of glycerol-induced promoter. The three genes, tandemly arrayed in an expression cassette with a marker gene ura3, regulatory and targeting sequences (G3P dh promoter and XPR-like terminator, 28S rDNA as a target locus), were transferred into Yarrowia lipolytica cells. The obtained recombinant strain NCYC3825 was characterized at the molecular level and with respect to its biotechnological potential. Our experiments indicated that the novel recombinant strain stably borne one copy of the expression cassette and efficiently expressed heterologous alcohol oxidoreductase, while glycerol dehydratase and its reactivator were expressed at lower level. Comparative shake flask cultivations in glucose- and glycerol-based media demonstrated higher biomass production by the recombinant strain when glycerol was the main carbon source. During bioreactor (5 L) fed-batch cultivation in glycerol-based medium, the recombinant strain was characterized by relatively high biomass and lipids accumulation (up to 42 gDCW L-1, and a peak value of 38%LIPIDS of DCW, respectively), and production of high titers of citric acid (59 g L-1) and 2-phenylethanol (up to 1 g L-1 in shake flask cultivation), which are industrially attractive bioproducts. Conclusions Due to heterogeneous nature of the observed alterations, we postulate that the main driving force of the modified phenotype was faster growth in glycerol-based media, triggered by modifications in the red-ox balance brought by the wide spectrum oxidoreductase. Our results demonstrate the potential multidirectional use of a novel Yarrowia lipolytica strain as a microbial cell factory.