A halo around bacterial growth on a starch plate indicates the activity of which enzymes?

The presence of a halo around bacterial growth on a starch plate indicates the activity of amylase and oligo-1,6-glucosidase. Starch is a polysaccharide, and these enzymes are capable of breaking down starch into simpler sugars. Amylase hydrolyzes starch into oligosaccharides and maltose, while oligo-1,6-glucosidase further breaks down the oligosaccharides, especially those with branching, into glucose units.

When bacteria capable of producing these enzymes are grown on a starch plate, the enzymes diffuse into the surrounding medium, leading to the hydrolysis of starch. As starch is broken down, it gets depleted from the area surrounding bacterial growth, leading to a clear zone or halo that contrasts with the remaining blue-black color of the intact starch in the medium. This clear zone indicates that starch has been broken down by the enzymes, confirming the enzymatic activity of the bacteria.

In contrast, the other options involve different types of enzymes that do not play a role in starch hydrolysis. Catalase and urease are enzymes involved in processes like hydrogen peroxide breakdown and urea metabolism, respectively, while protease and lactase deal with protein and lactose breakdown. Oxidase and