Engineered bacteria pave the way for vegan cheese and yogurt

Bacteria are set to transform the future of dairy-free milk products. Scientists have successfully engineered E. coli to produce key milk proteins essential for cheese and yogurt production, without using any animal-derived ingredients. This paves the way for plant-based dairy alternatives that mimic traditional dairy at a molecular level but are sustainable and cruelty-free.

A recent study published in Trends in Biotechnology reported two methods for producing casein (a milk protein) that are nutritionally and functionally similar to bovine casein.

Casein is a highly sought-after component in both infant and adult diets, as it is digestible, of high quality, and provides several essential amino acids our body needs. The global casein market, valued at US$2.7 billion in 2023, comes at the cost of animal cruelty and high environmental impact. This rise in demand for sustainable and dairy-free options has led researchers to seek alternative methods of producing casein.

The food and pharmaceutical industries have utilized microorganisms as cell factories for the large-scale production of biomolecules, dietary supplements, and enzymes for quite some time. Scientists were curious to see if the same approach could be used for recombinant casein proteins, produced through genetic engineering in microbial cell factories. However, these techniques often fail to replicate a key factor that imparts casein its unique properties—phosphorylation, a biological process where a phosphate group is added to a protein.

Phosphorylation of serine residues (amino acid components) is critical for casein’s ability to bind calcium, which makes milk stable and provides it with nutritional properties. Calcium binding also ensures the formation of nanoscale protein structures called casein micelles, which act as delivery agents for bioavailable calcium and phosphate.

To overcome this issue, the researchers adopted two main strategies. First, they engineered bacteria to co-express three Bacillus subtilis protein kinases, which are enzymes that catalyze the addition of phosphate groups to proteins. Second, they designed a phosphomimetic version of αs1-casein, in which serine residues normally phosphorylated in the naturally occurring protein were replaced with aspartic acid to mimic the negative charge and functional effects of phosphorylation.

The team carried out structural analysis, calcium-binding tests, and simulated gastrointestinal digestion of the derived αs1-casein. The results indicated that both the phosphorylated and phosphomimetic caseins of bacterial origin had a high calcium-binding capacity, and their digestibility and structure were comparable to that of cattle-derived casein.

The researchers highlighted that while kinase-mediated phosphorylation provides a route for closely mimicking native casein, phosphomimetic casein provides a simpler path for producing functionally similar proteins. They also suggested that further quantitative analysis is required to fully unlock our ability to harness the microbial production of caseins for sustainable and cruelty-free dairy and food applications.

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