AN EXTRACELLULAR FACTOR REGULATING EXPRESSION OF THE CHROMOSOMAL AMINOGLYCOSIDE 2'-N-ACETYLTRANSFERASE OF PROVIDENCIA-STUARTII

The chromosomal anc(2')-Ia gene in Providencia stuartii encodes a hous ekeeping 2'-N-acetyltransferase [AAC(2')-Ia] involved in the acetylati on of peptidoglycan. In addition, the AAC(2')-Ia enzyme also acetylate s and confers resistance to the clinically important aminoglycoside an tibiotics gentamicin, tobramycin, and netilmicin. Expression of the na c(2')-Ia gene was found to be strongly influenced by cell density with a sharp decrease in aac(2')-Ia mRNA accumulation as cells approached stationary phase, This decrease was mediated by the accumulation of an extracellular factor, designated AR (for acetyltransferase repressing )-factor. AR-factor was produced in both minimal and rich media and ac ted in a manner that was strongly dose dependent, The activity of AR-f actor was also pH dependent, with optimal activity at pH 8.0 and above , Biochemical characterization of conditioned media from P. stuartii h as shown that AR-factor is between 500 and 1,000 Da in molecular size and is heat stable, In addition, AR-factor was inactivated by a variet y of proteases, suggesting that it may be a small peptide.