Akbar Espaillat

Abstract Most bacteria are surrounded by an essential protective mesh-like structure called peptidoglycan, made of glycan chains crosslinked through short peptides by enzymes known as transpeptidases. Of these, penicillin-binding DD-transpeptidases connect adjacent peptide stems between their 4th and 3rd amino acids (4,3-type), D-alanine and a meso-diaminopimelic acid (mDAP) in Gram negatives, whereas LD-transpeptidases make the 3,3-type between mDAP3 residues.

New Results doi: https://doi.org/10.1101/2023.07.19.549629 Abstract Selective forces in the environment drive bacterial adaptation to novel niches, choosing the fitter variants in the population. However, in dynamic and changing environments, the evolutionary processes controlling bacterial adaptation are difficult to monitor. Here, we follow 9 cystic fibrosis patients chronically infected with Pseudomonas aeruginosa, as a proxy for bacterial adaptation.

Highlights • The bacterial cell wall is crosslinked by d-amino acid-containing peptides • β-Lactam antibiotics interfere with cell-wall crosslinking • We developed a d-amino acid-based method for introducing synthetic crosslinks • The crosslinks protect Escherichia coli from broad-spectrum β-lactam antibiotics Summary Transpeptidation reinforces the structure of cell-wall peptidoglycan, an extracellular heteropolymer that protects bacteria from osmotic lysis.