I know that some microorganisms can get their nitrogen requirements met with inorganic substances such as nitrate salts or urea. Others need organic nitrogen sources such as peptones or amino acids. I am looking for some rules of thumb along these lines, e.g. "most fungi can be cultured with nitrates" or "gram-positive bacteria usually require amino acids". Any little bit of information you can offer could help; maybe we can come up with a rule of thumb if none exists.