Cellular Ag: Giving Your Plate a Biotech Reboot - Part 1
This is the first entry of a two-part blog.
As the world’s population continues to increase and climate change simultaneously brings unprecedented ecological transformations, the glaring issues with livestock production (particularly in developed nations) become hard to ignore. The vast quantity of land required, the greenhouse gases and environmental pollutants produced, and the uncomfortable reality of poor animal welfare are all spurring development of a biotechnology-driven alternative to satisfy public demand for animal-based foods. The emerging sector of ‘cellular agriculture’ proposes growing animal tissues and metabolic products (e.g., proteins) in a controlled, bioreactor setting (which may or may not involve transgenic microbes) rather than a farm. Products of cellular agriculture will likely range from foods to other materials such as cosmetics and textiles like leather, suede, and silk. The ‘Holy Grail’ of this burgeoning biotech sector, however, is meat- often referred to as ‘lab meat’, ‘clean meat’ or ‘cultured meat’. Although there are no commercially available formulations at the time of writing, institutional and private sector research (Table 1) has made impressive progress in successfully culturing meat. Start-ups such as Upside Foods (formerly Memphis Meats), Aleph Farms, and Finless Foods are developing cell-culture chicken, beef, and seafood, respectively. Products, particularly from Upside, are expected to hit the market in the next few years.
Table 1: List of representative (though not exhaustive) start-up biotechnology companies in food-focused cellular agriculture.
Biotechnological advancement is finally, as Winston Churchill put it, tackling “the absurdity of growing a whole chicken in order to eat the breast or wing” (1931), but culturing lab meat has not come without significant challenges, such as the complexity of composition, texture, whole-cut structure, and more broadly, economic feasibility. Lab culturing largely-although not entirely- takes meat production off the farm: To start a culture, multipotent stem cells (e.g., bovine embryonic, mesenchymal, or induced pluripotent stem cells) need to be extracted from the animal of interest. However, only a small number of cells need to be sampled at infrequent intervals. In vitro skeletal muscle cell production is stimulated as satellite cells (matured stem cells) differentiate into myoblasts, which propagate to myocytes very quickly. These undergo fusion to form myotubes, eventually turning into muscle fibers. However, muscle tissue alone does not create the taste and texture associated with meat products; fat cells, blood vessels, nerves, and other differentiated tissues are also key to the sensory experience. Although it is theoretically possible, and likely inevitable to culture more complex structural tissues in the future (i.e., to produce ‘whole cuts’), most institutional and commercial development currently focuses on growth of ‘muscle-fat organoid’ tissues, generally considered the minimally-simplistic cultured formulation (Figure 1). To achieve this, mesenchymal cells may also be differentiated to produce adipose tissue in separate culture, which is then combined with muscle tissue upon maturation to form the final product, likely a patty or nugget.
Figure 1: Conceptual diagram of cultured animal tissue production, given current technological limitations. Culturing parameters require optimization specific to the animal source, such as beef, pork, or chicken (pictured). Green italicized text proposes aspects of current design which may increase economic efficiency, quality or quantity of production, or reduce environmental impact/energy demand.
Aside from challenges associated with growth of complex tissues, lab meat tenderness is a current challenge as well. In the animal, endothelial secretions induce adipocyte differentiation, maturation of muscle cells, and adipogenesis- producing the familiar texture and tenderness. However, in vitro stimulation of this process results in accumulation of toxic compounds such as 3-isobutyl-1-methylxanthine. Multi-omic analysis of livestock genomes has helped to identify biomarkers for textural attributes including meat tenderness, so it is possible that gene editing could produce alternative avenues for improving this quality. Furthermore, maintaining cellular and subsequent tissue structure during culturing is crucial for not only texture, but also for production of complex, multi-cell-type tissues grown for whole cuts. This consideration precludes the use of cost-efficient stir tank reactors since these present a risk of high shear stress to cells. More complex designs such as fluidized bed reactors allow high-density culturing without mechanized mixing, but it is unclear if these systems could meet the demands of commercial scaling, since they have not been formulated above a 100L capacity.
Another growth limitation impacting palatability is cut thickness- any homogenous cell type is capped to around 1 cm in thickness, given limitations imposed by nutrient, oxygen, and waste diffusion through tissue in a bioreactor. Interestingly, oxygen diffusion through in vitro tissue cuts may be considerably less problematic in marine animal-based culturing compared to mammalian or avian systems. Land-dweller cell lines typically demand air saturation levels of 40-60% in culture, and although no published conditions for in vitro seafood cell cultures are available, it is known that some fish are tolerant of air saturation levels as low as 0.5%. For bovine, pork, and chicken cultures, however, this diffusion constraint implies the need for blood vessel/muscle tissue co-culture development, or complex scaffolding to allow improved diffusion, if a product such as steak is ever to be achieved. One such potential scaffolding innovation recently introduced is decellularized spinach leaves. Animal cell growth over the vascular leaf structure allows diffusion of oxygen and nutrients to interior satellite cells, maintaining their viability throughout culturing. Other advantages of decellularized spinach leaves include its edibility, precluding the need of additional, potentially complex innovation in de-scaffolding end products, as well as its ease of production.
Currently, a major challenge and economic limitation of the commercial production of cultured meat is the bioprocessing economy of scale. One such cost efficiency challenge is growth media formulation. Fetal Bovine Serum (FBS) is the research and industry-standard growth supplement for animal cell culturing (e.g., avian, mammalian, or fish), but its use for this application would undermine several goals and benefits of the innovation (e.g., animal welfare, land use sustainability). FBS is so universally used due to its inclusion of a wide range of growth factors, enzymes, electrolytes, etc. Thus, any alternative formulation of a defined and precise cell culture supplement will require extensive research to determine metabolic efficiency in response to variable composition and concentration of growth substrates. Additionally, formulation will likely need to be cell type-specific. Furthermore, the entire supply chain of these media components must be taken into consideration, especially given the inherent inefficiencies of nutrient utilization and waste-production by mammalian cells. Advances in the recycling of culture medias have been made in bacterial and algal growth scenarios, and development of techniques with mammalian, avian, and fish cultures will likely be an important step in reducing production costs looking forward.
Overall, development of the technology of cellular meat culturing has some steep challenges ahead. If these challenges are met, however, humanity may come to completely rethink their dinnerplate; a wider variety of meat options may become available, nutritional profiles and underlying environmental impacts of food options may be considered more carefully, and outlook on animal welfare may evolve considerably. In the second installment of this blog series, non-animal and protein-based sectors of cellular agriculture will be examined, as well as the pros and cons of the industry as a whole.
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