You acquire a soil sample and run an enrichment culture on it. You provide the organisms in the culture with all of the ingredients required for growth except for nitrogen. What result do you expect to have at the end of your experiment?

A) Nitrogen-fixing bacteria will significantly outnumber those incapable of fixing nitrogen.

B) Nitrogen-fixing bacteria will not be present in the culture.

C) Nitrogen-fixing bacteria will be present but not as significantly greater number than non-nitrogen-fixing species.

D) Nitrogen-fixing bacteria will be present, but will be significantly outnumbered by non-nitrogen-fixing species.

Nitrogen-fixing bacteria will significantly outnumber those incapable of fixing nitrogen

Explanation:

Nitrogen-fixing bacteria are capable of growing in a medium lacking organic Nitrogen. They convert (fix) atmospheric Nitrogen (Nitrogen is abundant in air) into organic substrates. Hence, they will grow in the enrichment medium described. This is the kind of medium used to isolate nitrogen-fixing bacteria.

Non-nitrogen fixing bacteria require an organic form of Nitrogen for growth. Hence, in a medium with no nitrogen, they will rely on the Nitrogen fixers. This means delayed growth for them.

A culture medium also has limited nutrients, so the slow growers will have little or no nutrients left.

Therefore, the Nitrogen fixers will have competitive advantage and significantly outnumber those incapable fixing nitrogen.