Identification of bacterial transporters for hydroxyalkylcysteinylglycines

The generation of malodour in the human underarm (axilla) is caused by bacterial biotransformation of specific malodour precursor molecules contained within non-odorous apocrine gland secretions. The dipeptide-conjugated thioalcohol, (S)-(1-(2-hydroxyethyl)-1-methylbutyl)-L-cysteinylglycine (Cys-Gly-3M3SH) is known to be secreted into the axilla and biotransformed into the highly volatile thioalcohol 3-methyl-3-sulfanylhexan-1-ol (3M3SH) by members of the axillary microbiota, consisting principally of the genera Corynebacterium and Staphylococcus. However, the exact bacterial species that carry out this biotransformation have not been thoroughly characterised. Additionally, the route by which malodour precursor molecules are transported across the bacterial cell membrane to the cytoplasm have not been assessed, and a general disagreement within the literature is evident regarding the intracellular catabolic fate of such molecules.

Here, malodour precursor biotransformation data is presented from a library of skin isolated corynebacteria and staphylococci which identified significant variations in thioalcohol production across individual bacterial species and strains. Three Staphylococcus species, S. hominis, S. haemolyticus and S. lugdunensis were the strongest Cys-Gly-3M3SH biotransformers whereas all Corynebacterium spp. assessed showed weak or absent catabolism of this substrate. The molecular basis of uptake and biotransformation of dipeptide-conjugated malodour precursor compounds in the model organism Escherichia coli K-12 was assessed by creating and characterising peptide transporter deficient strains, which revealed novel phenotypes for several poorly studied peptide transporters in this organism. The relevant E. coli strains were then used as a background to overexpress and characterise putative dipeptide-conjugated malodour precursor transporters from a strong malodour producing S. hominis isolate. This revealed that a general S. hominis peptide transporter mediates Cys-Gly-3M3SH uptake. An in silico analysis of putative Cys-Gly-3M3SH catabolic genes revealed a novel cystathionine β-lyase-like gene present only in those Staphylococcus species able to biotransform Cys-Gly-3M3SH, strongly suggesting an involvement in Cys-Gly-3M3SH biotransformation.

This work provides major advances in understanding the molecular basis of human axillary malodour.