What distinguishes mycoplasmas from true bacteria?

Mycoplasmas are distinguished from true bacteria largely by the absence of a cell wall. This characteristic is fundamental to their classification because most true bacteria possess a rigid cell wall made up of peptidoglycan, which provides structural support and determines shape. The lack of a cell wall in mycoplasmas allows them a certain degree of flexibility and a distinctive morphology, often resulting in pleomorphic shapes.

This absence also impacts how mycoplasmas interact with their environment, as they are less susceptible to antibiotics that target cell wall synthesis—such as penicillin—which are effective against many other bacterial types. Moreover, this feature influences their ecological niche, as mycoplasmas are often found in more specific or favorable environments that allow them to thrive without the protective layer that cell walls provide.

The other choices address attributes that do not uniquely define mycoplasmas. For example, while some mycoplasmas can be anaerobic, not all are, and many true bacteria can grow in varying oxygen conditions. Similarly, mycoplasmas do not necessarily grow rapidly compared to other bacteria, and they do not have multiple nuclei, as their cellular structure is generally simpler.