CONTRIBUTION OF GENTAMICIN 2'-N-ACETYLTRANSFERASE TO THE O-ACETYLATION OF PEPTIDOGLYCAN IN PROVIDENCIA-STUARTII

A collection of Providencia stuartii mutants which either underexpress or overexpress aac(2')-Ia, the chromosomal gene coding for gentamicin 2'-N-acetyltransferase (EC 2.3.1.59), have been characterized phenoty pically as possessing either lower or higher levels of peptidoglycan O acetylation, respectively, than the wild type. These mutants were sub jected to both negative-staining and thin-section electron microscopy. P. stuartii PR100, with 42% O acetylation of peptidoglycan compared w ith 52% O acetylation in the wild type, appeared as irregular rods. In direct contrast, P, stuartii strains PR50,LM3 and PR51, with increase d levels of peptidoglycan O acetylation (65 and 63%, respectively), ap peared as coccobacilli and chain formers, respectively. Membrane blebb ing was also observed with the chain-forming strain PR51. Thin section ing of this mutant indicated that it was capable of proper constrictio n and separation, P. stuartii PM1, when grown to mild-exponential phas e, did not have altered peptidoglycan O-acetylation levels, and cellul ar morphology remained similar to that of wild-type strains. However, continued growth into stationary phase resulted in a 15% increase in p eptidoglycan O acetylation concomitant with a change of some cells fro m a rod-shaped to a coccobacillus-shaped morphology. The fact that the se apparent morphological changes were directly related to levels of O acetylation support the view that this modification plays a role in t he maintenance of peptidoglycan structure, presumably through the cont rol of autolytic activity.