A 17 KDA OUTER-MEMBRANE PROTEIN (OMP4) FROM SERRATIA-MARCESCENS CONFERS PARTIAL RESISTANCE TO BACTERIOCIN 28B WHEN EXPRESSED IN ESCHERICHIA-COLI

A cosmid-based genomic library of Serratia marcescens N28b was introdu ced into Escherichia coli and clones were screened for a bacteriocin 2 8b insensitive phenotype. One clone was found that showed partial resi stance to bacteriocin 28b. By using Tn5tac1 insertions it was shown th at this phenotype was due to the expression in E. coli of an outer-mem brane protein of 17 kDa (Omp4). The DNA region defined by insertion mu tagenesis was sequenced and found to contain an ORF of 515 bp. The ded uced amino acid sequence has 172 residues with a theoretical molecular mass of 18.4 kDa. The protein contains an N-terminal signal sequence of 24 amino acid residues and, when compared to other enterobacterial outer-membrane proteins, most closely resembles a family of small oute r-membrane proteins of Enterobacteriaceae whose known functions appear to be related with virulence. Immunoblotting experiments showed that Omp4 is present in 15 biotypes of S. marcescens. The bacteriocin 28b r esistance phenotype conferred on E. coil by Omp4 appears to be pleiotr opic since overexpression of the Omp4-encoding gene leads to a decreas e in the amount of OmpA, OmpF and/or OmpC; OmpA and OmpF are the recep tors for bacteriocin 28b in E. coli.