When food is reheated in a microwave oven, bacterial endospores are killed.

A. Use of microorganisms to produce useful products: This describes biotechnology in general but not specifically recombinant DNA technology.

B. Selective breeding of organisms to create new combinations of traits: Selective breeding involves natural mating, not direct genetic modification.

C. Study of replication and recombination in microbes: This is part of microbial genetics, not recombinant DNA technology.

D. Study of genetic expression in microbes: This focuses on gene regulation, not the deliberate manipulation of DNA.

E. Deliberate modification of the genome of an organism for practical purposes: This defines recombinant DNA technology, which involves inserting, deleting, or altering genes to achieve specific outcomes.

A. Parasitic: A parasitic relationship benefits the microbe at the host’s expense and typically causes harm; producing vitamin K for the host does not fit the parasitic definition.

B. Saprobic: Saprobic organisms obtain nutrients from dead or decaying organic matter (decomposers); intestinal E. coli living on host-derived substrates and contributing vitamins are not acting as saprobes.

C. Antagonistic: Antagonistic interactions involve one organism inhibiting another (competition or antimicrobial production); the described vitamin-producing relationship does not reflect antagonism.

D. Mutualistic: Mutualism describes a relationship where both partners benefit — E. coli gains a habitat and nutrients while the host gains vitamin K — which fits this scenario.