Question

c. Cellular respiration tests: Catalase.: positive result look like? positive result tell you about the organism? you use for this test? What does a What does a What solution did Oxidase.: What is this test detecting? if an organism is negative? that allows you to determine if an organism is What does it mean What is in the strip positive? Nitrate Reduction: What does this test look for? What does a positive test look like? What does a negative result look like?

Answer 1

Catalase test

What does a positive result look like?

Continuous bubble formation when hydrogen peroxide introduced to organism

What does the positive result will tell you about organism?

Positive result will tell that the organism is aerobic.

During aerobic respiration H2 may combine with O2, forming hydrogen peroxide (H₂O₂), which is lethal to the cell. Enzyme catalase is produced by most aerobic organism, to avoid lethal effect of H₂O₂. Catalase breaks down hydrogen peroxide into water and oxygen.

What solution did you use for this test?

Hydrogen peroxide

Oxidase test

What is this test detecting?

This test is detecting presence of cytochrome C in bacteria.

Cytochrome C is a component of the cytochrome C oxidase system which is an enzyme of bacterial electron transport chain. Some aerobic bacteria contain cytochrome C.

What does it mean if an organism is negative?

If an organism is negative for the test its mean it do not contain cytochrome C oxidase that oxidizes the test reagent but such bacteria can still be aerobic or facultative. They may require via some other oxidase in electron transport.

What is the strip that allows you to determine if an organism is positive?

Strip of Whatman’s No. 1 filter paper soaked in a freshly prepared 1% solution of tertramethyl-p-phenylene-diamine dihydrochloride allows to determine if an organism is positive. Colonies of bacteria are smeared on the moist strip. Intense deep-purple hue within 5-10 seconds, indicate positive reaction.

Nitrate Reduction

What does this test look for?

This test look for the ability or inability of bacteria to convert nitrate to nitrite. Enzyme nitrate reductase hydrolyze nitrate (NO3^-) to nitrite (NO2^-).

What does a positive test look like?

Formation of red compound with addition of sulfanilic acid and a red precipitate after addition of alpha- naphthylamine in the same test tube shows presence of nitrite.

What does a negative test look like

If no red colour precipitate are formed after addition of sulfanilic acid and α-naphthylamine means only that nitrite is not present in the medium.

2 possibilities are there

1. The strain do not reduce nitrate to nitrite. Such strains are called nitrate negative.

2. The strain reduced nitrate to nitrite which has then been completely reduced to nitric oxide, nitrous oxide, or nitrogen. And hence it will not react with the reagents that give red precipitate with nitrite. The strain is nitrate-positive.

in such case zinc powder is use to test if the organism has reduced nitrate beyond nitrite.. Zinc powder convert nitrate to nitrite, so red color after addition of zinc powder shows organism not capable of reducing nitrate. Absence of red colour shows the organism reduced nitrate to one of other nitrogen compound.