L-form bacteria, also known as L-phase bacteria, L-phase variants or cell wall-deficient bacteria (CWDB), are growth forms derived from different bacteria. They lack cell walls. Two types of L-forms are distinguished: unstable L-forms, spheroplasts that are capable of dividing, but can revert to the original morphology, and stable L-forms, L-forms that are unable to revert to the original bacteria.
Transmission electron micrograph of L-form Bacillus subtilis. The cells lack the electron-dense cell wall of normal bacteria. Scale bar is 500 nanometers.
Transmission electron micrograph of a population of L-form Bacillus subtilis, showing a range of sizes. Scale bar is 10 micrometers.
Phase contrast image of L-form cells from Bacillus subtilis showing a range of sizes. Scale bar is 5 micrometers.
A cell wall is a structural layer that surrounds some cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, and functions as a selective barrier. Another vital role of the cell wall is to help the cell withstand osmotic pressure and mechanical stress. While absent in many eukaryotes, including animals, cell walls are prevalent in other organisms such as fungi, algae and plants, and are commonly found in most prokaryotes, with the exception of mollicute bacteria.
Photomicrograph of onion root cells, showing the centrifugal development of new cell walls (phragmoplast)