Cell Wall Bioactive Molecules as Signaling and Effector Agents in Bacterial Physiology and Virulence

Fernando Baquero, Juan A. Ayala, Rafael Cantón

The molecules that make up the bacterial cell wall should be seen not only as passive structural components of the murein sacculus that protect and enclose the inner membrane containing the bacterial cytoplasm. They are also active bioactive molecules released during bacterial replication, especially after cell lysis, leading to a deconstructive process. These molecules vary in structure from simple acetylated monosaccharides or amino acids, such as D-amino acids, to more complex muropeptides and cross-linking peptides. They can be classified as Cell Wall Bioactive Molecules (CWBAMs), which have signaling and effector roles that affect bacterial physiology, including biofilm formation, sporulation, and antibiotic resistance. CWBAMs also participate in interactions with other bacteria, the microbiota, and immune cells from human and animal organs, including the central nervous system. The effects of CWBAMs released during cell wall breakdown remain largely unknown, especially since they can translocate from mucosal surfaces colonized by microbiota into the bloodstream. CWBAMs are not necessarily toxins and should be distinguished from endotoxins. Their role in bacterial-host interactions is a promising area for future research.