There are two main bacterial kingdoms, eubacteria (or Bacteria) and archaebacteria (Archaea). Bacteria are split into two broad domains, distinguished by the way in which they may be colored by a pigment (the "Gram" test). Bacillus subtilis is the universally recognized model for eubacteria of the sporulating A+T-rich Gram positive category. Gram-positives have a single envelope, comprising a lipid bilayer (cytoplasmic membrane) and a more or less complex set of protective layers. Bacillus subtilis is both a model for bacteria used in agro-food industry, and for dangerous pathogens.
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