The importance and future of biochemical engineering

Manipulating gene expression levels in mammalian cell factories: An outline of synthetic molecular toolboxes to achieve multiplexed control

Mammalian cells have developed dedicated molecular mechanisms to tightly control expression levels of their genes where the specific transcriptomic signature across all genes eventually determines the cell's phenotype. Modulating cellular phenotypes is of major interest to study their role in disease or to reprogram cells for the manufacturing of recombinant products, such as biopharmaceuticals. Cells of mammalian origin, for example Chinese hamster ovary (CHO) and Human embryonic kidney 293 (HEK293) cells, are most commonly employed to produce therapeutic proteins. Early genetic engineering approaches to alter their phenotype have often been attempted by "uncontrolled" overexpression or knock-down/-out of specific genetic factors. Many studies in the past years, however, highlight that rationally regulating and fine-tuning the strength of overexpression or knock-down to an optimum level, can adjust phenotypic traits with much more precision than such "uncontrolled" approaches. To this end, synthetic biology tools have been generated that enable (fine-)tunable and/or inducible control of gene expression. In this review, we discuss various molecular tools used in mammalian cell lines and group them by their mode of action: transcriptional, post-transcriptional, translational and post-translational regulation. We discuss the advantages and disadvantages of using these tools for each cell regulatory layer and with respect to cell line engineering approaches. This review highlights the plethora of synthetic toolboxes that could be employed, alone or in combination, to optimize cellular systems and eventually gain enhanced control over the cellular phenotype to equip mammalian cell factories with the tools required for efficient production of emerging, more difficult-to-express biologics formats.

Biocatalyst for the synthesis of natural flavouring compounds as food additives: Bridging the gap for a more sustainable industrial future

Biocatalysis entails the use of purified enzymes in the manufacturing of flavouring chemicals food industry as well as at the laboratory level. These biocatalysts can significantly accelerate organic chemical processes and improve product stereospecificity. The unique characteristics of biocatalyst helpful in synthesizing the environmentally friendly flavour and aroma compounds used as a food additive in foodstuffs. With methods like enzyme engineering on biotechnological interventions the efficient tuning of produce will fulfil the needs of food industry. This review summarizes the biosynthesis of different flavour and aroma component through microbial catalysts and using advanced techniques which are available for enzyme improvement. Also pointing out their benefits and drawbacks for specific technological processes necessary for successful industrial application of biocatalysts. The article covers the market scenario, cost economics, environmental safety and regulatory framework for the production of food flavoured chemicals by the bioprocess engineering.

Bioeconomy and net-zero carbon: lessons from Trends in Biotechnology, volume 1, issue 1

Many biotechnology applications tend to be for low production volumes and relatively high-value products such as insulin and vaccines. More difficult to perfect at scale are bioprocesses for high-volume products with lower value, especially if the target product is a reduced chemical such as a solvent or a plastic. Historically, industrial microbiology succeeded under special circumstances when fossil feedstocks were either unavailable or expensive. Inevitably, as these circumstances relaxed, bioprocesses struggled to compete with petrochemistry. Why try to compete? Fossil resources will be phased out in the coming decades in the struggle with climate change. To reach net-zero carbon by 2050 will require all sectors to transition, not only energy and transportation. This may herald a new opportunity for industrial bioprocesses with much better tools.

Applicability of Control Materials To Support Gene Promoter Characterization and Expression in Engineered Cells Using Digital PCR

The use of standardized components and processes in engineering underpins the design-build-test model, and the engineering of biological systems is no different. Substantial efforts to standardize both the components and the methods to validate the engineered biological systems is ongoing. This study has developed a panel of control materials encoding the commonly used reporter genes GFP and RFP as DNA or RNA molecules. Each panel contained up to six samples with increasingly small copy number differences between the two reporter genes that ranged from 1- to 2-fold differences. These copy number differences represent the magnitude of changes that may need to be measured to validate an engineered system. Using digital PCR (dPCR), we demonstrated that it is possible to quantify changes in both gene and gene transcript numbers both within and between samples down to 1.05-fold. We corroborated these findings using a simple gene circuit within a bacterial model to demonstrate that dPCR was able to precisely identify small changes in gene expression of two transcripts in response to promoter stimulation. Finally, we used our findings to highlight sources of error that can contributed to the measurement uncertainty in the measurement of small ratios in biological systems. Together, the development of a panel of control materials and validation of a high accuracy method for the measurement of small changes in gene expression, this study can contribute to the engineering biology "toolkit" of methods and materials to support the current standardization efforts.

Simplified Gene Knockout by CRISPR-Cas9-Induced Homologous Recombination

Genetic engineering of industrial cell lines often requires knockout of multiple endogenous genes. Tools like CRISPR-Cas9 have enabled serial or parallelized gene disruption in a wide range of industrial organisms, but common practices for the screening and validation of genome edits are lacking. For gene disruption, DNA repair by homologous recombination offers several advantages over nonhomologous end joining, including more efficient screening for knockout clones and improved genomic stability. Here we designed and characterized a knockout fragment intended to repair Cas9-induced gene disruptions by homologous recombination. We identified knockout clones of Komagataella phaffii with high fidelity by PCR, removing the need for Sanger sequencing. Short overlap sequences for homologous recombination (30 bp) enabled the generation of gene-specific knockout fragments by PCR, removing the need for subcloning. Finally, we demonstrated that the genotype conferred by the knockout fragment is stable under common cultivation conditions.

Bioelectrosynthesis systems

Bioelectrosynthesis (BES) systems exploit extracellular electron transport pathways to augment cellular metabolism. This strategy can be used to improve the economic viability of bio-based syntheses versus conventional methods, most notably petrochemical-based syntheses. It also has the potential to reduce the carbon footprint of biomanufacturing processes. Efficient channeling of cathode-derived electrons towards biosynthesis requires a better understanding of the biological mechanisms of electron transport as well as detailed evaluation of all aspects of process performance. More advanced solutions may deploy cell free systems that use ex situ generated reducing equivalents to improve economic performance.

Biotechnologies to Bridge the Schism in the Bioeconomy

Schism is the new normal for the bioeconomy concept. Since its proliferation in governments, the concept has been adapted to fit national or regional exigencies. Earlier this century the knowledge-based bioeconomy (KBBE) in Europe was seen as a technical and knowledge fix in the evolving sustainability landscape. At the OECD, the concept was further honed by imagining a future where biotechnologies contribute significantly to economic growth and development. Countries started to make national bioeconomy strategies. Some countries have diverged and made the bioeconomy both much larger and more general, involving a wide variety of sectors, such as industry, energy, healthcare, agriculture, aquaculture, forestry and fishing. Whatever the approach, what seems to be consistent is the need to reconcile environmental, social and economic sustainability. This paper attempts to establish one schism that could have ramifications for the future development of the bioeconomy. Some countries, including some of the largest economies but not exclusively so, are clearly following a biotechnology model, whereas others are clearly not. In the wake of the COVID-19 pandemic, biotechnologies offer outstanding potential in healthcare, although this sector is by no means included in all bioeconomy strategies. The paper also attempts to clarify how biotechnologies can address the grand challenges and the United Nations Sustainable Development Goals. The communities of scientists seem to have no difficulty with this, but citizens and governments find it more difficult. In fact, some biotechnologies are already well established, whereas others are emerging and more controversial.

Improving the activity and thermostability of GH2 β-glucuronidases via domain reassembly

Glycoside hydrolase family 2 (GH2) enzymes are generally composed of three domains: TIM-barrel domain (TIM), immunoglobulin-like β-sandwich domain (ISD), and sugar-binding domain (SBD). The combination of these three domains yields multiple structural combinations with different properties. Theoretically, the drawbacks of a given GH2 fold may be circumvented by efficiently reassembling the three domains. However, very few successful cases have been reported. In this study, we used six GH2 β-glucuronidases (GUSs) from bacteria, fungi, or humans as model enzymes and constructed a series of mutants by reassembling the domains from different GUSs. The mutants PGUS-At, GUS-PAA, and GUS-PAP, with reassembled domains from fungal GUSs, showed improved expression levels, activity, and thermostability, respectively. Specifically, compared to the parental enzyme, the mutant PGUS-At displayed 3.8 times higher expression, the mutant GUS-PAA displayed 1.0 time higher catalytic efficiency (k_cat /K_m ), and the mutant GUS-PAP displayed 7.5 times higher thermostability at 65°C. Furthermore, two-hybrid mutants, GUS-AEA and GUS-PEP, were constructed with the ISD from a bacterial GUS and SBD and TIM domain from fungal GUSs. GUS-AEA and GUS-PEP showed 30.4% and 23.0% higher thermostability than GUS-PAP, respectively. Finally, molecular dynamics simulations were conducted to uncover the molecular reasons for the increased thermostability of the mutant.

Systematic use of synthetic 5'-UTR RNA structures to tune protein translation improves yield and quality of complex proteins in mammalian cell factories

Predictably regulating protein expression levels to improve recombinant protein production has become an important tool, but is still rarely applied to engineer mammalian cells. We therefore sought to set-up an easy-to-implement toolbox to facilitate fast and reliable regulation of protein expression in mammalian cells by introducing defined RNA hairpins, termed 'regulation elements (RgE)', in the 5'-untranslated region (UTR) to impact translation efficiency. RgEs varying in thermodynamic stability, GC-content and position were added to the 5'-UTR of a fluorescent reporter gene. Predictable translation dosage over two orders of magnitude in mammalian cell lines of hamster and human origin was confirmed by flow cytometry. Tuning heavy chain expression of an IgG with the RgEs to various levels eventually resulted in up to 3.5-fold increased titers and fewer IgG aggregates and fragments in CHO cells. Co-expression of a therapeutic Arylsulfatase-A with RgE-tuned levels of the required helper factor SUMF1 demonstrated that the maximum specific sulfatase activity was already attained at lower SUMF1 expression levels, while specific production rates steadily decreased with increasing helper expression. In summary, we show that defined 5'-UTR RNA-structures represent a valid tool to systematically tune protein expression levels in mammalian cells and eventually help to optimize recombinant protein expression.