A method for displaying a recombinant polypeptide on the surface of a host cell, said method comprising the steps: (a) providing a host cell transformed with a nucleic acid fusion operatively linked with an expression control sequence, said nucleic acid fusion comprising: (i) a portion encoding a signal peptide, (ii) a portion encoding the recombinant polypeptide to be displayed, (iii) a portion encoding a transmembrane linker, and (iv) a portion encoding the transporter domain of an EhaA protein, and (b) culturing the host cell under conditions wherein the nucleic acid fusion is expressed and the expression product comprising the recombinant polypeptide is displayed on the surface of the host cell, wherein the host cell is a Gram negative bacterium, with the proviso that the Gram negative bacterium is not E. coli, and wherein the transporter domain of the EhaA protein (iv) consists of a sequence selected from the group consisting of: (a) an amino acid sequence comprising SEQ ID NO:19, (b) sequences which are at least 95%, at least 98 %, or at least 99% identical to the sequence of (a), and (c) a sequence encoded by a sequence selected from (i) a nucleotide sequence comprising SEQ ID NO:18, (ii) a nucleotide sequence encoding SEQ ID NO:19, (iii) nucleotide sequences comprising a sequence being at least 95%, at least 98 %, or at least 99% identical to SEQ ID NO:18 or/and a nucleotide sequence encoding SEQ ID NO:19, and (iv) nucleotide sequences which encode the polypeptides encoded by (i), (ii) or/and (iii) within the scope of the degeneracy of the genetic code. (a) providing a host cell transformed with a nucleic acid fusion operatively linked with an expression control sequence, said nucleic acid fusion comprising: (i) a portion encoding a signal peptide, (ii) a portion encoding the recombinant polypeptide to be displayed, (iii) a portion encoding a transmembrane linker, and (iv) a portion encoding the transporter domain of an EhaA protein, and (i) a portion encoding a signal peptide, (ii) a portion encoding the recombinant polypeptide to be displayed, (iii) a portion encoding a transmembrane linker, and (iv) a portion encoding the transporter domain of an EhaA protein, and (b) culturing the host cell under conditions wherein the nucleic acid fusion is expressed and the expression product comprising the recombinant polypeptide is displayed on the surface of the host cell, (a) an amino acid sequence comprising SEQ ID NO:19, (b) sequences which are at least 95%, at least 98 %, or at least 99% identical to the sequence of (a), and (c) a sequence encoded by a sequence selected from (i) a nucleotide sequence comprising SEQ ID NO:18, (ii) a nucleotide sequence encoding SEQ ID NO:19, (iii) nucleotide sequences comprising a sequence being at least 95%, at least 98 %, or at least 99% identical to SEQ ID NO:18 or/and a nucleotide sequence encoding SEQ ID NO:19, and (iv) nucleotide sequences which encode the polypeptides encoded by (i), (ii) or/and (iii) within the scope of the degeneracy of the genetic code. (i) a nucleotide sequence comprising SEQ ID NO:18, (ii) a nucleotide sequence encoding SEQ ID NO:19, (iii) nucleotide sequences comprising a sequence being at least 95%, at least 98 %, or at least 99% identical to SEQ ID NO:18 or/and a nucleotide sequence encoding SEQ ID NO:19, and (iv) nucleotide sequences which encode the polypeptides encoded by (i), (ii) or/and (iii) within the scope of the degeneracy of the genetic code.