starch agar experiment

hi i was wondering if anyone has done this...if so can u help
i've done the experiment but need help with a few questions
1. Wat r the two main ingredients of starch agar plates and wat are they're roles in the experiment?
2. why was there a blue ring outside the methylene blue well?
3. why did the starch agar plates turn black with iodine, but there were clear rings around the wells?
4. how would you test for the presence of a cellulase enzyme?

tnx
any help would be much appreciated :P

Reply 1

Spudder

1. Starch and agar? For evidence of saprophytic digestion.
2. Not sure about this one
3. Starch test with potassium iodine solution turns starch blue-black. There are clear areas where the starch has been digested by amylase enzymes secreted by the fungus.
4. I do not know this personally, but I found a method known as the 'Rapid Tube Test' for detecting fungal cellulase production:

"A simple procedure is described for the detection of cellulolytic activity in fungi, utilizing dyed cellulose powder as substrate. The powder, incorporated into a basal medium containing agar, mineral salts, and growth factors, is layered onto basal medium minus cellulose. Cellulase production results in release of the dye which diffuses into the lower layer."

Hope I was some help.

Reply 2

sheepishgurl

im guessing it has something to do with the breakdown of starch by an extracellular enzyme, namely, amylase. the white rings indicates the breakdown of starch. so im guessing, the larger the radius of the clear/white ring, the more starch is broken down.

hope i was of some help.