The closely related lantibiotics epidermin and gallidermin are produced by Staphylococcus epidermidis Tu3298 and S. gallinarum Tu3928, respectively. The epidermin biosynthetic genes involved in maturation, regulation, and immunity have been identified previously. How epidermin or gallidermin is secreted, however, has remained unclear. Here, we characterize two additional genes, epiH and epiT, as well as the homologous gallidermin genes gdmH and gdmT. EpiT and GdmT are similar to one-component ABC transporters that are involved in the secretion of proteins or peptides. EpiH and GdmH are hydrophobic proteins without conspicuous similarities to other proteins. Comparison of the gene sequences revealed that epiT is incomplete, having an internal deletion that causes a frame shift and a second deletion at the 3'-end, while gdmT is intact. Introduction of epiT and epiH into the heterologous host S. carnosus (pTepi14) bearing the maturation and regulation genes had no significant effect on the rather low level of epidermin production. The presence of the homologous gdmT and gdmH, however, resulted in a strong increase (seven- to tenfold) in the production level, which is very likely to be due to increased efficiency of epidermin secretion. Both gdmT and gdmH were necessary for this effect, indicating that the two gene products cooperate in some way. In the epidermin-producing wild-type strain Tu3298, which contains epiH and the disrupted epiT, the addition of gdmT alone led to a two-fold increase in epidermin production. Both gdmT and gdmH and the corresponding epi genes were activated by the transcriptional regulator EpiQ; this is in accordance with the presence of putative EpiQ operator sites in the promoter regions.

The biosynthetic gene clusters of the staphylococcal lantibiotics epidermin and gallidermin are distinguished by the presence of the unique genes epiH and gdmH, respectively. They encode accessory factors for the ATP-binding cassette transporters that mediate secretion of the antimicrobial peptides. Here, we show that gdmH also contributes to immunity to gallidermin but not to nisin. gdmH alone affected susceptibility to gallidermin only moderately, but it led to a multiplication of the immunity level mediated by the FEG immunity genes when cloned together with the gdmT gene, suggesting a synergistic activity of the H and FEG systems. gdmH-related genes were identified in the genomes of several bacteria, indicating an involvement in further cellular functions.Many gram-positive bacteria produce antimicrobial peptides (bacteriocins) active against other gram-positive strains. The activity of type A lantibiotics is based on pore formation in the cytoplasmic membrane. They contain unusual thioether bridges that arise from the posttranslational modification of cysteine and serine or threonine residues (for reviews, see references 2, 3, 5, and 20). The gene clusters of lantibiotics, such as nisin (produced by Lactococcus lactis), subtilin (produced by Bacillus subtilis), epidermin, and Pep5 (both produced by Staphylococcus epidermidis) comprise very similar sets of genes; the roles of most of them have been elucidated. We have previously characterized the epidermin genes for peptide synthesis (epiA) (21), maturation (epiB, -C, and -D) (9, 10, 16), processing (epiP) (4), and regulation (epiQ) (14) in the heterologous cloning host Staphylococcus carnosus. The genes epiF, -E, and -G encode the subunits of an ATP-binding cassette ABC exporter that confers on the producer immunity to epidermin by expelling the antimicrobial peptides from the cytoplasmic membrane (12, 15).The epidermin transporter gene epiT has been shown to be defective, since it is disrupted by a deletion causing a frameshift. The gdmT gene of the closely related lantibiotic gallidermin from Staphylococcus gallinarum, however, is intact and mediated a considerable increase of epidermin production when cloned in epidermin-producing strains. This effect was dependent on the presence of the adjacent gene, gdmH, indicating that GdmH acts as an accessory factor for the ATPbinding cassette transporter GdmT (18). gdmH encodes a membrane protein without similarity to proteins of known function. Homologous genes are lacking in all lantibiotic gene clusters except those of the epidermin and gallidermin determinants.GdmH contributes to producer immunity. The sensitivities to gallidermin of S. carnosus strains bearing gdmH alone or in combination with other members of the gene clusters (Fig. 1) were analyzed. Since only part of the gdmFEG operon was available, the epiFEG operon was used. The Epi and Gdm proteins have a high degree of identity, and several genes of the two gene clusters have been shown to be interchangeable (11,18). In order to combine functional FEG...

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