Final answer:
A virus is the microbe that is acellular and acts as a parasite of cells, existing on the edge of what is considered living and nonliving.
Step-by-step explanation:
The type of microbe that is a parasite of cells, is acellular, and bridges the gap between living and nonliving is a virus. Viruses are unique in that they lack cellular structure, are not considered alive outside of a host, and require a host's cellular machinery to replicate. They are considerably smaller than prokaryotic cells and lack components such as cell membranes, ribosomes, and the ability to metabolize on their own. Instead, they contain genetic material and protein structures that allow them to infect host cells and co-opt the host's mechanisms to produce more virions. Although they do not fit neatly into the category of living organisms, they share genetic material and the capability to evolve, which places them in a kind of netherworld on the spectrum of life.