an exoenzyme that hydrolyzes starch into mono- and dissacharide subunits.
In this photograph, two microorganisms were streaked on starch
agar and allowed to incubate. After incubation, the plate
was flooded with iodine. Iodine binds to starch but not to its breakdown
products, so a clear zone will appear around the streak of organism that
B. subtilis produces the exoenzyme, but S. epidermidis
Lipase is an
exoenzyme that hydrolyzes lipids into fatty acids and glycerol. In
this photograph, two organisms were streaked on a plate of spirit
blue agar. This agar contains lipids and spirit blue dye.
If a microorganism produces lipase, the fats around the streak are decomposed,
causing a clear zone to appear. The spirit blue dye also migrates
through the plate toward the region lacking complete lipids, resulting
in the appearance of a dark blue halo around the organism.
S. epidermidis produces lipase. E. coli does
Proteases hydrolyze proteins into polypeptides and amino acid subunits. Below are two examples of digestive proteases.
an exoenzyme that hydrolyzes the milk protein casein. In this photograph,
a plate of skim milk agar has been streaked
with Bacillus subtilis. As the casein is hydrolyzed around
the streak, a clear halo appears.
Gelatinase is a protease exoenzyme that hydrolyzes gelatin. These two tubes were produced by stabbing a single microorganism in a nutrient gelatin deep, then incubated at 37o C for 48 hours.
Tube A contains E. coli. This
organism does not produce gelatinase, so the deep remains solid.
Tube B contains Pseudomonas aeruginosa. This organism produces
the exoenzyme, so the deep has liquified.