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Bacteria are tested for amylase an exoenzyme that hydrolyzes starch. Exoenzymes are secreted by
bacteria and act outside the cell in the surrounding microenvironment. Iodine is added to the starch
plates to test for starch hydrolysis. If starch is still present then a very dark brown color will appear this
is due to the Iodine binding to any available starch (this is a negative result). If amylase is present then
the starch around the colonies will be broken down to the point that Iodine cannot bind to the starch
molecules these areas will appear lighter then the rest of the plate (this is a positive result).
1 Amylase Positive, 2 Amylase Negative, 3 Amylase Negative,4 Amylase Negative