Cell Wall Remodeling of Staphylococcus aureus in Live Caenorhabditis elegans.

Peptidoglycan (PG) scaffolds are critical components of bacterial cell walls. They counter internal turgor pressure to prevent lysis and protect against external insults. It was recently discovered that various types of bacteria release large quantities of PG building blocks (d-amino acids) into their surrounding medium. Contrarily, cultured bacteria were also found to incorporate d-amino acids (both natural and synthetic) from the medium directly into their PG scaffold. These two processes may potentially function, in concert, to metabolically remodel PG in live host organisms. However, demonstration that bacteria can decorate their cell surfaces with exogenous d-amino acids was limited to in vitro culture conditions. We present the first evidence that bacteria remodel their PG with exogenous d-amino acids in a live host animal. A tetrazine click partner was conjugated onto the side chain of a d-amino acid to capture incorporation into the bacterial PG scaffold using a complementary click-reactive fluorophore. Staphylococcus aureus infected Caenorhabditis elegans treated with exogenous d-amino acids readily revealed in vivo PG labeling. These results suggest that extracellular d-amino acids may provide pathogens with a mode of late-stage in vivo cell-surface remodeling.