"Lean meat" is a misleading term. I noticed many times in conversations that people who think that they eat "proteins" tend to think about this food group as an almost pure protein, a perfect set of essential amino acids. Especially if they consume so called "lean meats."
In beef (presented as "90% lean meat") - half of the calories are from fat (http://nutritiondata.self.com/facts/beef-products/6193/2). Even in the leanest bird meat approximately the fifth of the energy is from fat, ~18% in the leanest I could find (http://nutritiondata.self.com/facts/poultry-products/704/2).
Digestibility-corrected amino acid score (PDCAAS) of protein in beef is only 0.92, chicken - 0.91(?), and egg whites and soy - 1 or 100% (not that it matters much). Note, that 62% of calories in a whole egg are from fat, and 40% in soybeans.
Archaea and bacteria (eubacteria) are single-celled organisms that do not have a nucleus or organelles. Archaea have a distinct evolutionary history and biochemistry compared with bacteria.
Archaea - a domain of single-celled microorganisms. These microbes are prokaryotes. Archaea can survive in extreme and harsh environments like hot springs, salt lakes, marshlands, oceans, gut of ruminants and humans.
Bacteria - a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Eubacteria are ubiquitous and are found in soil, hot springs, radioactive waste water, Earth's crust, organic matter, bodies of plants and animals, etc.