ABSTRACT
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-kDa bacteriolytic enzyme LytFM, originally isolated from the spent HDM growth medium, may contribute to bacteriolytic activity previously detected by zymography at 14 kDa 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 lytFM in the genomes of nine Gram-positive bacteria from surface-sterilised HDM, and the expression by these isolates of LytFM and its variants LytFM1/LytFM2. The lytFM 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 LytFM1 was detected in culture supernatants of these bacteria by mass spectrometry (MS) and ELISA, and the bacterial LytFM proteins were shown by zymography to be able to hydrolyse peptidoglycan. Our previous reports of LytFM 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 LytFM1 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.
ABSTRACT
A 14 kDa protein homologous to the γ-d-glutamyl-l-diamino acid endopeptidase members of the NlpC/P60 Superfamily has been described in Dermatophagoides pteronyssinus and Dermatophagoides farinae but it is not clear whether other species produce homologues. Bioinformatics revealed homologous genes in other Sarcopteformes mite species (Psoroptes ovis and Blomia tropicalis) but not in Tetranychus urticae and Metaseiulus occidentalis. The degrees of identity (similarity) between the D. pteronyssinus mature protein and those from D. farinae, P. ovis and B. tropicalis were 82% (96%), 77% (93%) and 61% (82%), respectively. Phylogenetic studies showed the mite proteins were monophyletic and shared a common ancestor with both actinomycetes and ascomycetes. The gene encoding the D. pteronyssinus protein was polymorphic and intronless in contrast to that reported for D. farinae. Homology studies suggest that the mite, ascomycete and actinomycete proteins are involved in the catalysis of stem peptide attached to peptidoglycan. The finding of a gene encoding a P60 family member in the D. pteronyssinus genome together with the presence of a bacterial promotor suggests an evolutionary link to one or more prokaryotic endosymbionts.
ABSTRACT
Dust mites produce bacteriolytic enzymes, one of which belongs to the NlpC/P60 superfamily comprising bacterial and fungal proteins. Whether this enzyme is derived from the mite or from mite-associated microbes is unclear. To this end, the bacteriology of mites per se, and carpet and mattress dust from a group of asthmatic children and their parents was investigated. Dust from parents' and children's mattresses yielded significantly more colony forming units compared with dust from their corresponding carpets. Zymography demonstrated some dusts contained bacteriolytic enzymes, and in nine of the twelve dust samples from three of five houses examined, a prominent bacteriolytic band was obtained that corresponded to the mite band, although in one home, other lytic bands were detected. Fifty bacterial isolates were obtained from surface-sterilised, commercially obtained Dermatophagoides pteronyssinus. 16S rRNA, tuf and rpoB gene sequencing of nine Gram-positive isolates identified them as Bacillus cereus, B. licheniformis, Staphylococcus aureus, S. epidermidis, S. capitis and Micrococcus luteus, known human skin commensals. 16S rRNA sequence homologies of four of the nine isolates identified as B. licheniformis formed a distinct phylogenetic cluster. All species secreted lytic enzymes during culture although the lytic profiles obtained differed between the rods and the cocci, and none of the bands detected corresponded to those observed in dust or mites. In conclusion, mites harbour a variety of bacterial species often associated with human skin and house dusts contain bacteriolytic enzymes that may be mite-derived. The identification of a novel cluster of B. licheniformis isolates suggests an ecological adaptation to laboratory-reared D. pteronyssinus. It remains to be determined whether the previously described mite-associated 14 K lytic enzyme is derived from a microbial source.
