One of the most important structures in nature is the cell wall. Not every living thing has them. Mammals, fish, squid, and insects get along fine without them. But plants, fungi and bacteria depend on them for various reasons, like keeping the cells together.

“Plant cells are swollen almost to the breaking point,” according to Kerwyn Casey Huang of Stanford University, and the rigid walls keep them from bursting.

But many species of bacteria shed their cell walls. The reasons are not fully understood, said Dr. Huang, a professor of bioengineering, but there are theories. For instance, an attack by immune cells can make the bacteria cells shed their walls, perhaps because there are parts of the wall that the immune system recognizes and attacks. So the bacteria without a cell wall might be hiding, in effect, even though it may also explode because the membranes containing it aren’t strong enough.

Even more surprising, bacteria like the much studied E. coli can grow the walls back.

“How could this possibly happen?” Dr. Huang said. It’s a question he and Gabriel Billings, a doctoral student in his laboratory, are trying to answer, working with other colleagues at Stanford and Princeton.