"Single Cell Protein is the Ultimate Alternative Protein"

There are a lot of companies attempting to figure this stuff out and here is as good a primer as you are likely to find.
From Nanalyze:

There are people who live to eat and others who eat to live. This article is mostly going to appeal to the latter group – those who would be happy to nosh on 3D-printed pizza or exist on a steady diet of powdered soylents. We’ve been writing a series on the rise of alternative proteins to stone age mainstays like meat and milk. From growing beef in a lab to milking microbes for eggs, our food system is about to get very Jetsons-like very soon. Ironically, many of the advances rely on some of the most simple organisms on the planet: single-cell microbes like bacteria. Life wouldn’t be possible without these microorganisms, which are responsible for little things like soil fertility and human digestion. Soon they could be used as a major source of nutrition as part of a growing food sector known as single-cell protein.

What is Single-Cell Protein?
In the past, we’ve talked mainly about three different kinds of alternative proteins. One is the popular plant-based products like those created by Beyond Meat (BYND) and Impossible Foods. Then there are a ton of companies either growing meat or seafood using animal cells. Finally, there’s another cohort of startups genetically modifying microorganisms like yeast in order to use fermentation to brew proteins with similar structures to milk or even gelatin. In that case, microbes are separated from the final product and discarded.

A list of the most popular bacteria used in commercial applications of SCP. One comment: Ram horn? Credit: Frontiers in Microbiology

That brings us to Single-Cell Protein (SCP). If your preferred footwear in summer or winter is Birkenstocks with socks, then you’re probably familiar with a couple of types of SCPs such as nutritional yeast and spirulina. And if you talk with a funny accent, then you’ve also consumed Saccharomyces cerevisiae (the same species of yeast used in brewing) in the form of Vegemite or Marmite. In fact, there are a number of single-celled microbes and algae with commercial value as food, usually containing at least 30% protein and a healthy dose of amino acids.

Advantages of Single-Cell Protein 
Not only are some single-cell proteins highly nutritious, but they’re extremely fast-growing and require much less input compared to Daisy the cow. For instance, the yeast used in the black tar known as Vegemite is a byproduct of the beer brewing process....

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