"His research showed that specific types of microorganisms tended to exist in certain proportions in healthy soil environments and in water. From this he developed the formula for Effective Microorganisms™, a proprietary and trademarked formula sold through EM Research Organization affiliate offices throughout the world, which contains specific types of Lactobacillus, Phototrophic Bacteria (PNSB), and Yeasts."
I think SBO is mainly a commercial name. I can't find anything scientific that contain the name. It is just a catchy way to name organisms derived from soil (and sometimes, even when they're not from soils at all).