Cultured meat is produced using animal muscle cells, which typically require animal serum for their growth. However, the use of serum presents major challenges due to its high expense and ethical dilemmas. Recently, researchers have created a system where liver cells that secrete growth factors are grown alongside photosynthetic microorganisms, establishing a cost-effective and eco-friendly medium for cultivating muscle cells without animal serum.
As global food demand rises, there is an urgent need for sustainable meat production methods. Cultured meat technology, which has been gaining traction as an alternative to traditional meat production, was first introduced in 2012 and involves cultivating muscle cells from animals in laboratory settings.
The standard process for producing cultured meat involves using serum (the liquid component of blood) from animals, essential for the growth of muscle cells due to its rich protein content. The reliance on animal serum creates challenges, including high costs, contamination risks, and ethical issues. Consequently, it is necessary to develop culture techniques that enable muscle cells to grow serum-free.
A research team led by Professor Tatsuya Shimizu from Tokyo Women’s Medical University, along with Ph.D. student Shanga Chu, Professor Toru Asahi from Waseda University, Professor Yuji Haraguchi from Tokyo Women’s Medical University, and Professor Tomohisa Hasunuma from Kobe University, has created a novel system that cultures muscle cells without serum by utilizing photosynthetic microorganisms. Their research findings were published in Scientific Reports on August 23, 2024.
Typically, animal serum supplies proteins known as growth factors that are critical for muscle cell growth. Interestingly, rat liver cells are also capable of producing these growth factors. The scientists found that the liquid left after culturing these liver cells (referred to as supernatant) is rich in growth factors and can support muscle cell growth without requiring serum. “While growing more factors-secreting cells and cultivating for longer periods can yield a greater quantity of growth factors, the trade-off is that these cells also release waste products like lactate and ammonia, which can impair muscle cell growth,” explains Shimizu.
Thus, removing waste is vital to enhance the efficacy of this supernatant as an alternative to animal serum. To tackle this, the researchers developed L-lactate-consuming cyanobacteria (a type of photosynthetic microorganism) equipped with genes that convert lactate to pyruvate, allowing them to absorb harmful wastes such as lactate and ammonia and convert them into usable nutrients (like pyruvate and amino acids) for both rat liver and muscle cells.
In their study, the team proposed a new system where growth-factor producing rat liver cells are co-cultured with the modified cyanobacteria. The resulting supernatant from this co-culture can then be used to enhance muscle cell growth without the need for serum. They observed that this co-culture significantly reduced lactate by 30% and ammonia by over 90%. Additionally, the nutrients synthesized by the cyanobacteria helped mitigate nutrient depletion caused by rat liver cells, leading to a richer supply of nutrients, including glucose and pyruvate, in the co-culture supernatant compared to the supernatant from liver cells alone.
Using this co-culture supernatant to cultivate muscle cells resulted in a growth rate that was three times higher than that achieved with just rat liver cells. This indicates that co-culturing with cyanobacteria greatly enhances the effectiveness of the culture supernatant as a replacement for serum, optimizing the cell culture process through waste transformation.
“Our research presents an innovative, low-cost, and sustainable cell culture system that can be widely applied in various sectors of cellular agriculture, including cultured meat production, fermentation, biopharmaceutical manufacturing, and regenerative medicine. Moreover, this method for producing meat without harming animals may help tackle not only future food security challenges but also ethical considerations and climate change issues,” concludes Shimizu.
