Protein degradation may take place intracellularly or extracellularly. In digestion of food, digestive enzymes may be released into the environment for extracellular digestion whereby proteolytic cleavage breaks proteins into smaller peptides and amino acids so that they may be absorbed and used. In animals the food may be processed extracellularly in specialized organs or guts, but in many bacteria the food may be internalized via phagocytosis. Microbial degradation of protein in the environment can be regulated by nutrient availability. For example, limitation for major elements in proteins (carbon, nitrogen, and sulfur) induces proteolytic activity in the fungus "Neurospora crassa" as well as in of soil organism communities.