Calculate the number of times the DNA of a modern E. coli cell has been copied accurately since its earliest bacterial precursor cell arose about 3.5 billion years ago. Assume for simplicity that over this time period, E. coli has undergone, on average, one cell division every 12 hours (this is an overestimate for modern bacteria, but probably an underestimate for ancient bacteria).

#Question id: 40225

#Applied Microbiology

Read the following statements regarding cloning vectors and select the correct option.

Statement I: Antibiotic resistance markers are essential for an expression vector but not necessary for a standard cloning vector.

Statement II: The presence of an antibiotic resistance gene allows transformed bacteria to survive on media containing the corresponding antibiotic.

#Question id: 40226

#Applied Microbiology

Assertion (A): When plating bacteria after a transformation experiment, adding ampicillin to the agar plates is crucial if the plasmid vector carries the ampR gene.

Reason (R): Ampicillin acts as a nutrient source for the bacteria that have successfully taken up the plasmid.

#Question id: 40227

#Applied Microbiology

Which of the following microorganisms is a free-living, aerobic, chemoorganotrophic nitrogen fixer?

#Question id: 40228

#Applied Microbiology

Consider the following statements regarding nitrogen-fixing bacteria:

• Statement I: Rhizobium forms a symbiotic association with leguminous plants and fixes nitrogen only within the root nodules.

• Statement II: Alcaligenes species are primarily known as anaerobic chemolithotrophs in the nitrogen cycle.

#Question id: 40229

#Applied Microbiology

Assertion (A): Photosynthetic bacteria like Rhodobacter can fix atmospheric nitrogen.

Reason (R): These bacteria possess the nitrogenase enzyme complex, which is sensitive to oxygen.

#Question id: 40230

#Applied Microbiology

Match the specialized structures/enzymes with the corresponding nitrogen fixer: