Peptidoglycan is a complex biopolymer that is unique to bacteria. Glycan strands attached to short peptides that are crosslinked to one another form a chain link fence-type structure that acts as the bacterial skeleton. In Gram negative bacteria, the PG is a thin layer found in the periplasm, between the inner and outer membranes. Maintaining the integrity of PG is crucial to bacterial viability. We are interested in understanding how large protein complexes such as flagella, pili, secretion systems and efflux pumps are inserted through the PG layer without compromising cellular integrity. Are they inserted as the PG is made, or afterwards by making holes?
Because PG is so important for bacterial survival, its remodelling (which is required for cell elongation and division) is carefully regulated by a number of enzymes that make and break the bonds between sugars (glycosylases), between amino acids (peptidases) and between sugar and amino acid (amidases).
We screened a library of Pseudomonas mutants lacking individual PG enzymes to identify those with a role in trans-envelope protein complex formation. To date we have identified proteins involved in flagellar swimming motility, twitching motility and type II secretion, and in antibiotic resistance. Our results show that each PG enzyme has a specific, non-redundant role to play in cell wall metabolism.