Can single cellular organisms like bacteria or yeast be genetically modified to serve as efficient food sources?

[cirosantilli]

There seem to be no decent naturally occurring ones: https://www.quora.com/Can-bacteria-be-cultivated-as-a-source-of-food

I guess this comes down to how does wheat look like in the microscope? Hugely fat cells with nutrients, or raw elements?

Just considering if there's a way to make more efficient food sources without dealing with the complexities of programming a multicelular being.