Extracellular Enzymes
Environmental bacteria such as Bacillus species often produce extracellular enzymes to degrade substances such as proteins, lipids, and starch. These enzymes can be tested for using the following kinds of differential media.
Starch media: Starch media contains the polysaccharide starch as a substrate. Organisms which produce amylase and maltase and are able to hydrolyze starch will show a zone of clearing around the growth of the microorganism.
Lipid media: Lipid media contains the lipid substrate Tributyrin. Organisms which produce lipase and are able to hydrolyze lipids will show a zone of clearing around the growth of the microorganism.
Casein media: Casein media contains the substrate casein, which is a major milk protein. Organisms which produce protease and/or casease and are able to hydrolyze casein will show zone of clearing around the growth of the microorganism.
This plate is positive for starch and lipid hydrolysis, and weakly positive for casein hydrolysis. Note the zones of clearing in the media around the bacterial growth. (Iodine has been added to the starch sector to aid in seeing starch hydrolysis.)
This plate is negative for starch and lipid hydrolysis, and positive for casein hydrolysis. Note the absence of a zone of clearing in the starch and lipid sectors.