Question

You perform a citrate test on a microbe and observe a blue color in the tube the following day; What does htis indicate? Is the microbe a heterotroph or autotroph? Why do you think so?

Answer 1

Answer -

Citrate test is used to check whether the microbe can utilise citrate as the carbon source or not. As in the medium only citrate is present as a carbon source, thus the microbe have to utilise the citrate as only carbon source for it's growth and survival and when that microbes uses citrate as carbon source, a color change observes in the test tube turing initial green to blue color. This indicates that the microbe is using citrate as carbon source for growth.

Heterotrophs are those which cannot make their own food (in scirntific term startch or glucose or basically acarbon source for energy) thus, heterotrophs have to rely on outer source as carbon source for growth while autotrophs are those which can make their own food means they can synthesize their own starch and glucose and thus, they don't have to depend on outer carbon source.

As, in the given experiment the microbe is utilizing citrate as carbon source turning the test tube color from green to blue infers that it cannot synthesize it's own food. Therefore, it must be an heterotrophic microbe.