Semisynthesis of a Bacterium with Non-canonical Cell-Wall Cross-Links.

The cell wall is an elaborate framework of peptidoglycan that serves to protect the bacterium against osmotic challenge. This exoskeleton is composed of repeating saccharides covalently cross-linked by peptide stems. The general structure of the cell wall is widely conserved across diverse Gram-negative bacteria. To begin to explore the biological consequence of introducing non-canonical cross-links into the cell wall of Escherichia coli, we generated a bacterium where up to 31% of the cell-wall cross-links are formed by a non-enzymatic reaction between a sulfonyl fluoride and an amino group. Bacteria with these non-canonical cell-wall cross-links achieve a high optical density in culture, divide and elongate successfully, and display no loss of outer membrane integrity. This work represents a first step in the design of bacteria with non-canonical "synthetic" cell walls.