Studies of an iron-regulated bacteriocin-like substance in Aeromonas sp.
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Aeromonas is a ubiquitous aquatic bacterium that causes serious infections in both cold- and warm-blooded animals, including humans. Various researchers have reported the production of an inhibitory substance that shows antimicrobial activity against different indicator bacteria. Here we present a case where an environmental isolate of Aeromonas salmonicida, designated as Aeromonas strain 92, produces a bacteriocin-like substance (BLS) that is negatively regulated by the presence of iron. Various properties associated with Aeromonas strain 92 BLS were determined and its proteinaceous nature was established. The bacteriocidal/bacteriostatic mode of action of BLS against the indicator bacterium Serratia marcescens was successfully demonstrated. A sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS-PAGE) analysis between high-iron and low-iron culture conditions and Matrix Assisted Laser Desorption Ionization – Time Of Flight (MALDI-TOF) MS/MS analysis determined that BLS is likely to be the AsaP1 protein, a metallo-endopeptidase. This protein is highly expressed during the low-iron condition and displays antimicrobial activity against several different indicator bacteria. The gene encoding AsaP1 was ligated into the pBAD202 vector and was successfully transformed into Escherichia coli competent cells. The total lysate of a transformant shows antimicrobial activity against the indicator bacterium, but the expression of recombinant AsaP1 protein under L-arabinose induction couldn’t be verified by SDS-PAGE.