Dermatophagoides pteronyssinus lytFM encoding an NlpC/P60 endopeptidase is also present in mite‐associated bacteria that express LytFM variants

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‐ 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.

Origins of peptidases

“…In family G2, the bacterial homologues are mostly from Firmicutes, and in families S73 and S74, from Proteobacteria. Families C40, M23, M60 and N10 also have eukaryote and/ or archaean homologues, presumably the result of horizontal gene transfers, but only the C40 peptidase LytFM from the house dust mite (Dermatophagoides pteronyssinus) has been characterized [32]. The only peptidase family that contain homologues from dsDNA virus and eukaryotes (in addition to those listed above for mimiviruses) is C19.…”

The protozoanTrichomonas vaginalistargets bacteria with laterally-acquired NlpC/P60 peptidoglycan hydrolases

“…Consistent with relatively ancient LGT event(s) into the Trichomonas lineage, analyses of GC% profile variation of the nine scaffolds encoding the nine TvNlpC/P60 genes, we observed that seven genes were located in segments with average GC% composition characteristic of the T. vaginalis genome (~31-32 GC%) and were not located close to segmentation points (S1 Table and S6 Fig). This is in contrast to the relatively recent candidate LGT likely derived from a bacterial donor from the urogenital tract identified on a ~53 kbp T. vaginalis genome sequence scaffold [35]. A segment of ~34 kbp encodes 27 proteins highly similar (range: 79–98% identity) and with long stretches of gene synteny with the bacteria Peptoniphilus harei .…”

“…One gene derived from a ground water metagenome [33], member of the major bacterial TM6 lineage (accession KKP35888.1), was included as it clustered within a well-supported clan that included the sequence from the free-living protist Acantamoeba castellanii , a published candidate LGT for this species [34] (Fig 1). Additional published NlpC/P60 candidate LGTs in eukaryotes were also considered including genes from Fungi and mites [35], providing a far more appropriate phylogenetic framework to investigate the tempo and mode of LGT for all nine TvNlpC/P60 sequences compared to published analyses, which only considered one TvNlpC/P60 sequence and bacterial sequences [14,18].…”

Characterisation of three novel β-1,3 glucanases from the medically important house dust mite Dermatophagoides pteronyssinus (airmid)

“…The unexpected discovery of an endo-β-1,3 glucanase in the Antarctic springtail, Cryptopygus antarcticus was explained by horizontal gene transfer (HGT) (Song et al, 2010). Thus, the presence of β-1,3 glucanases in the genome of D. pteronyssinus may also point to acquisition by HGT, as HGT has been seen previously in this species (Tang et al, 2017).…”