There are many bacteria which synthesize and secrete so called exoenzymes. These are large protein molecules that have an essential purpose in appropriate bacterial metabolism. Microbes require a wide range of nutrition which is often hard to access for them. Most of these aliments are biopolymers, such as amilose and amylopectin (the components of starch), DNA, or casein (the main protein component of milk), fats, etc. These are called polymers, because they are constructed of lot (poly) of repeated molecular segments constituting to their enormous size. It is a bit sloppy comparison, but if you have ever been in a hurry and tried to eat something in seconds, you must have experienced how hard it is to send down huge chunks of food on your throat. It is kind of the same with bacteria, they can’t take up extreme sized molecules at once. Just as you better use a knife to slice up a cake before biting in it, they need these exoenzymes to do some of the cleaving job for them. The word exo- refers to the notion that these enzymes are transported into the ‘outer world’ and that the partial degradation of biopolymers are done outside the cells.
The result of a positive casease test. Those crosses are the
bacteria we inocluated on the Petri. That transparent area
is due to the degraded casein.
Agar dish containing blood. In the lower right corner you
can see an alpha hemolyis.
Here are the skyscrapers of 'test tube city' we used
for the plenty of other experiments in order to characterize our strains.