Journal of Biotechnology

The use of plants as biofactories presents as an attractive technology with the potential to efficiently produce high-value human recombinant proteins in a cost-effective manner. Plastid genome transformation stands out for its possibility to accumulate recombinant proteins at elevated levels. Of particular interest are recombinant growth factors, given their applications in animal cell culture and regenerative medicine. In this study we produced recombinant human Fibroblast Growth Factor (rhFGFb), a crucial protein required for animal cell culture, in tobacco chloroplasts. We successfully generated two independent transplastomic lines that are homoplasmic and accumulate rhFGFb in their leaves. Furthermore, the produced rhFGFb demonstrated its biological activity by inducing proliferation in HEK293T cell lines. These results collectively underscore plastid genome transformation as a promising plant-based bioreactor for rhFGFb production. Main conclusionWe generated transplastomic tobacco lines that stably express a human Basic Fibroblast Growth Factor (hFGFb) in their chloroplasts stroma and purified a biologically active recombinant hFGFb.

While bioactivity and a favorable safety profile for biotherapeutics is of utmost importance, manufacturability is also worth of consideration to ease the manufacturing process. Many biotherapeutics are typically expressed in mammalian cells. Process-related impurities or biological impurities like viruses and host cell proteins (HCP) are present in the harvest which have mostly acid isoelectric points and need to be removed to ensure safety for the patients. Therefore, during molecule design, an isoelectric point of the target molecule should preferably differ sufficiently from the isoelectric points of the impurities to enable an efficient and straightforward purification strategy. In this feasibility study we have evaluated the possibility to improve manufacturability by increasing the isoelectric point of the target protein. We have generated several variants of a GLP1-receptor-agonist-Fc-domain -FGF21 fusion protein and demonstrate that the critical anion exchange chromatography step can be run at high pH values with maximal product recovery theoretically allowing removal of HCP and viruses. Addressing the isoelectric point can be useful for an efficient process for removing HCP and viruses and this topic should be considered early in the research phase to ensure that other important molecule properties, e.g. safety, efficacy and expression yield are not impacted.

Bacterial nanocellulose (BC), a versatile and biodegradable polymer, has been extensively studied as an alternative biomaterial for various applications. For biomedical and packaging uses, where precise control over nanocellulose structure is essential, existing literature describes BC structural modification processes that involve additives or additional steps. With the aim to develop a programmable method to control the bulk microstructure, we developed sRNA-based post-transcriptional repression cassettes that allows precise regulation of the crystalline phase of BC. Before investigating the effects of post-transcriptional repression of bcsD, bcsZ, and ccpA genes, known to influence BC crystallinity, we validated the specificity of the sRNA repression cassette by targeting a genome-integrated red fluorescent protein, mRFP1. The observed growth inhibition (>80%) caused by overexpressed Hfq RNA chaperone in Komagataeibacter xylinus was alleviated ([≤] 23%) by its removal, resulting in a 43% reduction in relative mRFP1 expression. By varying the design of the repression cassette and the inducer concentrations, we successfully modulated the repression of the target genes [with relative expression reductions of 6%-34% for bcsD, 8%-24% for bcsZ, and 2%-20% for ccpA, as confirmed by qRT-PCR]. These gene repression levels led to statistically significant changes in the amorphous content of the BC microstructure, as demonstrated by X-ray diffraction and wide-angle X-ray scattering analysis.

A novel modified CHO cell line was constructed by expressing a three gene combination of Bclx(L), Aven and BECN1 which are critical targets of the apoptosis and autophagy pathways. This synergistic combination significantly improved cell viability as well as Rituximab (RTX) expression by 7.5 fold. A comparative amino acid analysis of the modified and control cultures both with and without RTX expression showed interesting changes in amino acid uptake rates. We first compared the utilization of amino acids in the control cells without RTX expression to the control cells with RTX expression where it declined significantly in the later half of the culture with the maximum decrease observed with tyrosine, which instead of uptake got secreted into the medium. The uptake of aspartic and glutamic acid also fell drastically during this period demonstrating the deleterious effect of RTX expression on cellular health. When the modified cells were used for RTX expression, there was conversely a slight increase in amino acid consumption in the later part of the culture with the maximum increase observed with alanine and tyrosine. The differential amino acid consumption rates provided us with an indirect measure of improved cellular health and ability of the modified cells to counter the cellular stress associated with RTX expression. Amino acid analysis could thus become a useful predictive tool to identify the critical features of better host expression platforms.

Geraniol is a monoterpene with wide applications in the food, cosmetics, and pharmaceutical industries. Microbial production has largely used model organisms lacking favorable properties for monoterpene production. In this work, we produced geraniol in metabolically engineered Yarrowia lipolytica. First, two plant-derived geraniol synthases (GES) from Catharanthus roseus (Cr) and Valeriana officinalis (Vo) were tested based on previous reports of activity. Both wild type and truncated mutants of GES (without signal peptide targeting chloroplast) were examined by co-expressing with MVA pathway enzymes tHMG1 and IDI1. Truncated CrGES (tCrGES) produced the most geraniol and thus was used for further experimentation. The initial strain was obtained by overexpression of the truncated HMG1, IDI and tCrGES. The acetyl-CoA precursor pool was enhanced by overexpressing mevalonate pathway genes such as ERG10, HMGS or MVK, PMK. The final strain overexpressing 3 copies of tCrGES and single copies of ERG10, HMGS, tHMG1, IDI produced approximately 1 g/L in shake-flask fermentation. This is the first demonstration of geraniol production in Yarrowia lipolytica and the highest de novo titer reported to date in yeast.

The Cell-PCA screen, since its inception, has provided an efficient method for analyzing cellular interactomes and has been used in various biological studies involving proteins like MYC, PER2, and ERK. With rapid advancements in biotechnology, including tools for protein function investigation, the Cell-PCA screen remains relevant. However, despite its successful application in recent studies, there are areas for optimization to ensure its continued relevance in the face of evolving technological advancements.

Naringenin, a flavanone and a precursor for a variety of flavonoids, has potential applications in the health and pharmaceutical sectors. The biological production of naringenin using genetically engineered microbes is considered as a promising strategy. The naringenin synthesis pathway involving chalcone synthase (CHS) and chalcone isomerase (CHI) relies on the efficient supply of key substrates, malonyl-CoA and coumaroyl-CoA. In this research, we utilized a soil bacterium, Acinetobacter baylyi ADP1, which exhibits several characteristics that make it a suitable candidate for naringenin biosynthesis; the strain naturally tolerates and can uptake and metabolize coumarate, a primary compound in alkaline-pretreated lignin and a precursor for naringenin production. A. baylyi ADP1 also produces intracellular lipids, such as wax esters, thereby being able to provide an excess of malonyl-CoA for naringenin biosynthesis. Moreover, the genomic engineering of this strain is notably straightforward. In the course of the construction of a naringenin-producing strain, the coumarate catabolism was eliminated by a single gene knockout ({Delta}hcaA) and various combinations of plant-derived CHS and CHI were evaluated. The best performance was obtained by a novel combination of genes encoding for a CHS from Hypericum androsaemum and a CHI from Medicago sativa, that enabled the production of 18 mg/L naringenin in batch cultivations from coumarate. Furthermore, the implementation of a fed-batch system led to a significant 3.7-fold increase (66 mg/L) in naringenin production. These findings underscore the potential of A. baylyi ADP1 as a host for naringenin biosynthesis as well as advancement of lignin-based bioproduction.

Abscisic acid (ABA) is a high-value product with agricultural, medical and nutritional applications. We previously constructed an ABA cell factory by expressing the ABA metabolic pathway from Botrytis cinerea in the biotechnological workhorse Saccharomyces cerevisiae. In this study, we aimed to improve ABA production and explored various rational engineering targets mostly focusing on increasing the activity of two rate-limiting cytochrome P450 monooxygenases of the ABA pathway, BcABA1 and BcABA2. We evaluated the effects of overexpression and knock-down of cell membrane transporters, expression of heterologous cytochrome b5, overexpression of a rate-limiting heme biosynthesis gene and overexpression or knock-out of genes involved in ER membrane homeostasis. One of the genes involved in ER membrane homeostasis, PAH1, was identified as the most promising engineering target. Knock-out of PAH1 improved ABA titers, but also caused a sever growth defect. By replacing the PAH1 promoter with a weak minimal promoter, it was possible to mediate the growth defect while still improving ABA production. In this report we were able to improve the ABA cell factory and furthermore provide valuable insights for future studies aiming to engineer cytochrome P450 monooxygenases. One-sentence summaryIn this study we explored various strategies to improve heterologous abscisic acid production in Saccharomyces cerevisiae and identified fine-tuning of the PAH1 gene as a promising engineering strategy.

Tacrolimus (FK-506) is a macrolide widely used as immunosuppressant to prevent transplant rejection. Synthetic production of FK-506 is not efficient and costly, whereas the biosynthesis of FK-506 is complex and the level produced by the wild type strain, Streptomyces tsukubaensis, is very low. We therefore engineered FK-506 biosynthesis and the supply of the precursor L-lysine to generate strains with improved FK-506 yield. To increase FK-506 production, first the intracellular supply of the essential precursor lysine was improved in the native host S. tsukubaensis by engineering the lysine biosynthetic pathway. Therefore, a feedback deregulated aspartate kinase AskSt* of S. tsukubaensis was generated by site directed mutagenesis. Whereas overexpression of AskSt* resulted only in a 17% increase in FK-506 yield, heterologous overexpression of a feedback deregulated AskCg* from Corynebacterium glutamicum was proven to be more efficient. Combined overexpression of AskCg* and DapASt, showed a strong enhancement of the intracellular lysine pool following increase in the yield by approximately 73% compared to the wild type. Lysine is coverted into the FK-506 building block pipecolate by the lysine cyclodeaminase FkbL. Construction of a {Delta}fkbL mutant led to a complete abolishment of the FK-506 production, confirming the indispensability of this enzyme for FK-506 production. Chemical complementation of the {Delta}fkbL mutant by feeding pipecolic acid and genetic complementation with fkbL as well as with other lysine cyclodeaminase genes (pipAf, pipASt, originating from Actinoplanes friuliensis and Streptomyces pristinaespiralis, respectively) completely restored FK-506 production. Subsequently, FK-506 production was enchanced by heterologous overexpression of PipAf and PipASp in S. tsukubaensis. This resulted in a yield increase by 65% compared to the WT in the presence of PipAf from A. friuliensis. For further rational yield improvement, the crystal structure of PipAf from A. friuliensis was determined at 1.3 [A] resolution with the cofactor NADH bound and at 1.4 [A] with its substrate lysine. Based on the structure the Ile91 residue was replaced by Val91 in PipAf, which resulted in an overall increase of FK-506 production by approx. 100% compared to the WT.

The COVID-19 pandemic, which is caused by SARS-CoV-2 has rapidly spread to more than 222 countries and has put global public health at high risk. The world urgently needs safe, a cost-effective SARS-CoV-2 coronavirus vaccine, therapeutic and antiviral drugs to combat the COVID-19. Angiotensin-converting enzyme 2 (ACE2), as a key receptor for SARS-CoV-2 infections, has been proposed as a potential therapeutic target in COVID-19 patients. In this study, we report high level production (about [~]0.75 g /kg leaf biomass) of glycosylated and non-glycosylated forms of recombinant human truncated ACE2 in Nicotiana benthamiana plant. The plant produced recombinant human truncated ACE2s successfully bind to the SARC-CoV-2 spike protein, but deglycosylated ACE2 binds more strongly than the glycosylated counterpart. Importantly, both deglycosylated and glycosylated forms of AEC2 stable at elevated temperatures for prolonged periods and demonstrated strong anti-SARS-CoV-2 activity in vitro. The IC50 values of glycosylated and deglycosylated AEC2 were 0.4 and 24 g/ml, respectively, for the pre-entry infection, when incubated with 100TCID50 of SARS-CoV-2. Thus, plant produced truncated ACE2s are promising cost-effective and safe candidate as a potential therapeutic targets in the treatment of COVID-19 patients.

Bispecific antibodies are at the forefront of biopharmaceutical drug development. With over 100 different molecular architectures combined with diverse individual subunit sequences, choosing the most suitable structure and predicting the ideal subunit expression ratios for successful heterodimerization is a significant challenge. In this paper, we demonstrate that the recently described cell line development paradigm shift (Rajendran et al. 2021), enabled by the Leap-In transposon platform, can be extended to the development of bispecific monoclonal antibody-producing cell substrates (stable clones and pools). The key features are 1) Parental pools reliably predict the derivative clonal productivity and clonal heterodimer fractions. 2) Clonal productivity and clonal heterodimer fraction remained stable for at least 60 population doublings. 3) Depending on the products biophysicochemical properties, the stable pools exhibit variable productivity stability. 4) Heterodimer fractions remain stable in the Leap-In mediated stable pools independently of the productivity stability of the pools. 5) Structures and subunit ratios can be triaged at stable pool level, and 6) Due to the homogeneous clonal productivity distribution, only a small number ([~]50) of clones need to be isolated and characterized.

The cytochrome P450 (CYP) monooxygenase superfamily offers the unique ability to catalyze regio-and stereospecifical oxidation of a non-activated C-H bond. CYPs found applications in the synthesis of pharmaceuticals and drug metabolites as well as in bioremediation. They are typically used in whole-cell bioconversion processes, due to their low stability and the need for a redox partner and cofactor. Unfortunately, substrate uptake and/or product transport limitations are frequently encountered and side reactions occur due to other enzymes in the cellular environment. Here, we present a proof-of-principle of a novel cell-free cytochrome P-450 nanocatalyst based on surface display on bacterial outer membrane vesicles. The self-sufficient CYP 102A1 from Bacillus megaterium was engineered to be translocated on the outer membrane vesicles of Escherichia coli. The resulting vesicles can simply be isolated from the culture supernatant. Moreover, no expensive and elaborate enzyme purification is required. This approach shows great promise as an alternative strategy to recombinantly produce CYP enzymes for a variety of applications, such as in fine chemical production and in the development of biosensors.

The suitability of rice yellow mottle virus RYMV as a gene expression vector in plant was assessed using a construct carrying promastigote surface antigen (PSA) C-terminal coding sequence of the parasite protozoan Leishmania. RYMV ORF1 encoding P1 protein has been deleted from the RYMV native genome. The C-terminal PSA gene was substituted for the viral coat protein. PSA is present at the surface of the parasite and displays vaccine properties against canine and human leishmaniosis. RYMV-based vector allowed PSA expression in Nicotiana benthamiana. Q-pcr analysis showed that chimeric RYMV carrying PSA gene is able to replicate in N. benthamiana leaves. P19 silencing suppressor in combination with the lacked viral vector ORF encoding RYMV Coat Protein (CP) enhanced significantly RYMV tool replication in N. benthamiana. RYMV CP played a key role on viral RNA stabilization and acts as a weak silencing suppressor. The original RYMV-based expression vector allowed PSA protein expression enhancement in N. benthamiana without any symptoms. RYMV-based vector could be suitable for functional genomic studies in monocots by VIGS (Viral Induced Gene Silencing) technology.

The limited number of well-characterized model bacteria cannot address all the challenges in a circular bioeconomy. Therefore, there is a growing demand for new production strains with enhanced resistance to extreme conditions, versatile metabolic capabilities, and the ability to utilize cost-effective renewable resources while efficiently generating attractive biobased products. Particular thermophilic microorganisms fulfill these requirements. Non-virulent Gram-negative Caldimonas thermodepolymerans DSM15344 is one such attractive thermophile that efficiently converts a spectrum of plant biomass sugars into high quantities of polyhydroxyalkanoates (PHA) - a fully biodegradable substitutes for synthetic plastics. However, to enhance its biotechnological potential, the bacterium needs to be "domesticated". In this study we established effective homologous recombination and transposon-based genome editing systems for C. thermodepolymerans. By optimizing the electroporation protocol and refining counterselection methods, we achieved significant improvements in genetic manipulation and constructed the AI01 chassis strain with improved transformation efficiency and a {Delta}phaC mutant that will be used to study the importance of PHA synthesis in Caldimonas. The advances described herein highlight the need for tailored approaches when working with thermophilic bacteria and provide a springboard for further genetic and metabolic engineering of C. thermodepolymerans, which can be considered the first model of thermophilic PHA producer.

Withdrawal StatementAfter publication, we discovered that the data presented in the manuscript do not correspond to the microbial strains described in the text. Specifically, the strains were mixed up during the analysis, which compromises the validity of the main conclusions. We take full responsibility for this oversight and are currently working to resolve the issue. In the interest of scientific accuracy and integrity, we believe that withdrawal is the most appropriate course of action at this time. Therefore, we do not wish this work to be cited as reference fort he project. We apologize for any confusion this may have caused and thank you for your understanding. If you have any questions, please contact the corresponding author.

Poly(A)-polymerase (PAP-1) from Escherichia coli is the primary enzyme responsible for synthesizing poly(A) tails on RNA molecules, signaling RNA degradation in bacterial cells. In vitro, PAP-1 is used to prepare libraries for RNAseq and to produce mRNA vaccines. However, E. coli PAP-1s toxicity and instability in low-salt buffers complicate its expression and purification. Here, we optimized the conditions for the production of recombinant PAP-1. For that, E. coli PAP-1 was expressed in seven E. coli strains with different origin and genetic backgrounds, followed by assessment of the overall protein yield, solubility, and enzymatic activity. Among the tested strains, BL21 (DE3) pLysS achieved the best balance of cell density, total PAP-1 yield, solubility, and specific activity. Rosetta 2 (DE3) and Rosetta Blue (DE3) hosting the pRARE plasmid exhibited the lowest solubility, likely due to excessive translation efficiency. Higher induction temperatures (>18{degrees}C) exacerbated PAP-1 insolubility. Interestingly, PAP-1 accumulation correlated with an increase in the plasmid copy number encoding the enzyme, indicating its potential utility as a surrogate marker for PAP-1 activity. These findings provide insights into optimizing E. coli PAP-1 production for biotechnological applications.

Innovative strategies for sustainable utilization of waste resources are imperative in the pursuit of a circular economy. Recently, the idea of utilizing mammalian spent media as a valuable resource is gaining traction, offering significant opportunities for innovative uses as a food-grade feedstock for microbial fermentation, especially in the production of alternative proteins for research and food purposes. In this study, we aim to repurpose spent mammalian culture media for production of valuable proteins. Growth factors (GFs) are a family of high-value proteins that naturally stimulate cell proliferation or differentiation. More importantly, these factors also present significant costs for cell culture. Here, we successfully demonstrate the use of spent mammalian culture media for the recombinant production of fibroblast growth factor 2 (FGF2-G3) in Lactococcus lactis. Bioreactor fermentation at a 1 L scale confirmed purified yields of 2.6 mg/L of recombinant FGF2-G3 using spent media. Further functional testing indicated that the recombinant FGF2-G3 can promote cell proliferation on an Anguilla japonica (Japanese eel) pre-adipocytic cell line, suggesting its potential for cultivated meat production. Based on the preliminary results of this study, our calculations indicate that fermenting 1 L spent mammalian waste could yield enough growth factors to efficiently grow approximately 52 L of cultivated meat through fermentation. This prediction emphasizes the potential of waste valorisation to sustainably produce protein, thus contributing to environmental preservation and economic viability. HighlightsO_LISpent mammalian culture media can be repurposed for microbial fermentation. C_LIO_LIGRAS L. lactis was used to express FGF2-G3 in an optimized spent media formulation. C_LIO_LIFunctional FGF2-G3 expression was demonstrated in controlled 1-L bioreactor runs. C_LI

The aqueous extract of Cynara cardunculus flowers is traditionally used in cheese production across Mediterranean countries. To meet the growing industrial demand for plant-based milk-clotting enzymes and to explore potential biotechnological applications, we initiated a study to heterologously produce cyprosin B (CYPB), a key milk-clotting enzyme from C. cardunculus, in Nicotiana benthamiana. We also investigated the role of its plant-specific insert (PSI) domain in the CYPBs activity and its localization. In this study, full-length CYPB and a PSI domain deleted CYPB (CYPB{Delta}PSI) were transiently expressed in N. benthamiana leaves using Agrobacterium-mediated infiltration. The leaves were harvested nine days post-infiltration, and proteins were purified, yielding approximately 81 mg/kg (CYPB) and 60 mg/kg (CYPB{Delta}PSI) fresh weight. CYPB{Delta}PSI showed significantly higher proteolytic activity (156.72 IU/mg) than CYPB (57.2 IU/mg), indicating that the PSI domain is not essential for enzymatic activity and that its removal results in enhanced enzymatic efficiency. In the milk-clotting activity assay, CYPB{Delta}PSI demonstrated a significantly faster clotting time than full-length CYPB, indicating enhanced milk-clotting efficiency for CYPB{Delta}PSI. Subcellular localization studies revealed that CYPB and PSI were localized in the vacuole and endocytic vesicles. In contrast, CYPB{Delta}PSI was primarily localized in the endoplasmic reticulum (ER) and the tonoplast, suggesting that the PSI domain is critical for vacuolar targeting and membrane permeabilization that affects overall protein yield. This study demonstrates the feasibility of using N. benthamiana as a platform for the scalable production of more efficient recombinant CYPB. It highlights the multifunctional role of the PSI domain in vacuolar sorting without impairing its functionality. These results underscore the potential of plant-based expression systems as a viable alternative for the industrial production of plant milk-clotting enzymes, with significant implications for sustainable cheese production.

The methylotrophic yeast Komagataella phaffii is a premier host for recombinant protein (rProt) production, traditionally relying on methanol induction of the alcohol oxidase 1 promoter (pAOX1). However, methanol flammability and associated industrial limitations have motivated the search for methanol-free induction systems. We recently demonstrated that disruption of formate dehydrogenase (FDH) in K. phaffii allows endogenous formate, derived from tetrahydrofolate (THF)-mediated C1 metabolism, to induce pAOX1 without addition of external inducers. Building on this, we hypothesized that increasing intracellular formate production by enhancing serine biosynthesis could further improve promoter induction and rProt productivity. Overexpression of SER3, encoding 3-phosphoglycerate dehydrogenase, the rate-limiting enzyme in serine synthesis, significantly increased pAOX1-driven expression of an intracellular reporter protein (eGFP) and secreted glucose oxidase (Gox) from Aspergillus niger, without compromising cell fitness. Enhanced formate accumulation and stronger pAOX1 induction were observed in both micro- and bioreactor cultivations using sorbitol or glycerol-sorbitol mixtures. In bioprocess conditions, SER3 overexpression led to a 30% increase in specific Gox activity compared to the parental FdhKO strain. This study provides a cost-effective metabolic engineering strategy for methanol-free, self-inducible expression systems in K. phaffii based on pAOX1, enabling safer and more sustainable industrial rProt production.

Heparosan is a precursor molecule for the widely used anticoagulant heparin, which also has other uses such as certain drug delivery applications and as a scaffold for tissue engineering in biomaterials. Traditionally, pathogenic bacteria such as E.Coli have been used as a host to produce heparosan as an alternative to animal and chemoenzymatic synthesis. Using GRAS status organisms like Lactococcus Lactis as the host for production of heparosan provides a safe alternative as well as being a well-established organism for genetic manipulation and reengineering. In this study, a functional heparosan synthesis pathway was successfully expressed in Lactococcus Lactis by the expression of E.coli K5 genes KfiA and KfiC, along with the overexpression of ugd, glmu and pgma genes present natively in the host organism. The genes were activated using the tightly controlled NICE expression system. The genes were cloned into plasmid p8148 and transformed into two strains, Lactococcus Lactis NZ9000 and Lactococcus Lactis NZ9020, totaling six different recombinant strains were created using these two hosts and various combinations of the heterologous genes. The recombinant Lactococcus Lactis SH6 strain, expressing the genes ugd-KfiA-KfiC-pgma yielded a maximum concentration of 754 mg/l in batch bioreactor experiments and the titer was increased to 1263 mg/l in fed-batch fermentation. NMR imaging successfully determined that the structure of the product derived from Lactococcus Lactis was indeed similar to E.coli heparosan. The molecular weight of heparosan varied from 10-20 KDa, indicating its potential use for chemoenzymatic heparin biosynthesis.