– EDA-DA is an unnatural dipeptide building block (an ethynyl-D-alanine and a D-alanine). It incorporates a biorthogonal alkyne group into peptidoglycan (PG) through MurF in the cytoplasmic pathway, which enables selective labeling via a click-chemistry reaction. EDA-DA allows labeling of PG in Gram-positive (B. subtilis), Gram-negative (E. coli and C. trachomatis), Mycobacterium (M. smegmatis) and moss plastids (P. patens) with azide modified fluorescent dyes such as Alexa Fluor 488.