Question

Starch hydrolysis What result would you expect if glucose had been added to the starch agar medium and then inoculated with B. megaterium or B. subtilis? Explain.

Answer 1

Answer - starch hydrolysis test include the testing of an organism whether it utilise starch for its energy need. Being a larger molecule it cannot be ingulfed by the bacteria so it secrete exoenzymes, including a-amylase and oligo-1,6-glucosidase, that hydrolyze starch and break into small components which then can be taken by bacteria easily. So whent iodine is added to the media it will turn blue or black where the bacteria has not break the starch while if the bacteria has break the starch then around it on adding the iodine there will be a clear zone because that area starch is utilised by the bacteria.

case - if the glucose is added to the starch medium

Answer - in this case as we are giving glucose as a source of energy which is the monomer of the starch or hydrolysed component of the starch so bacteria will easily utilise the the glucose which is added and the starch will remain unhydrolysed so when iodine will be added it will only give black colour in the complete starch agar plate hence in this way we won't be able to analyse whether the bacteria is starch hydrolyzing or not. Because we have diverted our experiment by adding the glucose.

Although two bacteria bacillus megaterium and bacillus subtilis both are starch hydrolyzing bacteria but as I told that the experiment is diverted by adding of glucose and this starch plate won't be able to suggest whether the bacteria is starch hydrolyzing or not

Case 2- after utilising the glucose

After utilising the added because if bacteria survive then they can hydrolysed the starch present in its vicinity and on adding the iodine give there will give clear zone around the bacteria while a blackor blue colour in the remaining area of the plate. This will suggest that the bacteria is starch hydrolysing

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