Peptidoglycan is a substance that forms the outermost portion of the cell walls in many bacteria. In the bacterial species where it is found, peptidoglycan is present as a rigid envelope surrounding the outside of the cytoplasmic membrane

Peptidoglycan is made up of glycosaminoglycan chains interlinked with short peptides. It helps provide the bacterial cell with vital mechanical rigidity and acts as a physical barrier against environmental stress while offering adequate plasticity to allow cell growth and division.