Biochemical Tests. Amylase Production (Starch Hydrolysis Test). Starch agar is a differential medium that tests the ability of an organism to produce certain exoenzymes, including α-amylase and oligo-1,6-glucosidase, that hydrolyze starch.
Starch agar before inoculation
Bacillus subtiliscolony on a culture medium containing starch. The culture plate has been flooded with a weak
iodine solution, which reveals a zone of clearing around the colony (arrow). This zone represents the area where the
starch has been hydrolyzed so that it is no longer available to react with the iodine solution.
Gelatin strip test. The organism on the left does not hydrolyze gelatin and, therefore, no clearing of the gelatin film is seen. On the right, the portion of the strip submersed in the organism suspension has cleared, indicating gelatin hydrolysis.