Dermatophagoides pteronyssinus lyt FM encoding an NlpC/P60 endopeptidase is also present in mite‐associated bacteria that express Lyt FM variants

The bodies and faecal pellets of the house dust mite ( HDM ), Dermatophagoides pteronyssinus , are the source of many allergenic and nonallergenic proteins. One of these, the 14‐ kD a bacteriolytic enzyme Lyt FM , originally isolated from the spent HDM growth medium, may contribute to bacteriolytic activity previously detected by zymography at 14 kD a in the culture supernatants of some bacterial species isolated from surface‐sterilised HDM . Based on previously reported findings of lateral gene transfer between microbes and their eukaryotic hosts, we investigated the presence of lyt FM in the genomes of nine Gram‐positive bacteria from surface‐sterilised HDM , and the expression by these isolates of Lyt FM and its variants Lyt FM 1/Lyt FM 2. The lyt FM gene was detected by PCR in the genomes of three of the isolates: Bacillus licheniformis strain 1, B. licheniformis strain 2 and Staphylococcus aureus . Expression of the variant Lyt FM 1 was detected in culture supernatants of these bacteria by mass spectrometry ( MS ) and ELISA , and the bacterial Lyt FM proteins were shown by zymography to be able to hydrolyse peptidoglycan. Our previous reports of Lyt FM homologues in other mite species and their phylogenetic analysis had suggested that they originated from a common mite ancestor. The phylogenetic analysis reported herein and the detection of other D. pteronyssinus proteins by MS in the culture supernatants of the three isolates that secreted Lyt FM 1 further support the hypothesis of lateral gene transfer to the bacterial endosymbionts from their HDM host. The complete sequence homology observed between the genes amplified from the microbes and those in their eukaryotic host indicated that the lateral gene transfer was an event that occurred recently.