A Newly Discovered Mycobacterial Pathogen Isolated from Laboratory Colonies of Xenopus Species with Lethal Infections Produces a Novel Form of Mycolactone, the Mycobacterium ulcerans Macrolide Toxin

Abstract

Mycobacterium ulcerans, the causative agent of Buruli ulcer, produces a macrolide toxin, mycolactone A/B, which is thought to play a major role in virulence. A disease similar to Buruli ulcer recently appeared in United States frog colonies following importation of the West African frog, Xenopus tropicalis. The taxonomic position of the frog pathogen has not been fully elucidated, but this organism, tentatively designated Mycobacterium liflandii, is closely related to M. ulcerans and Mycobacterium marinum, and as further evidence is gathered, it will most likely be considered a subspecies of one of these species. In this paper we show that M. liflandii produces a novel plasmid-encoded mycolactone, mycolactone E. M. liflandii contains all of the genes in the mycolactone cluster with the exception of that encoding CYP140A2, a putative p450 monooxygenase. Although the core lactone structure is conserved in mycolactone E, the fatty acid side chain differs from that of mycolactone A/B in the number of hydroxyl groups and double bonds. The cytopathic phenotype of mycolactone E is identical to that of mycolactone A/B, although it is less potent. To further characterize the relationship between M. liflandii and M. ulcerans, strains were analyzed for the presence of the RD1 region genes, esxA (ESAT-6) and esxB (CFP-10). The M. ulcerans genome strain has a deletion in RD1 and lacks these genes. The results of these studies show that M. liflandii contains both esxA and esxB.

Evolution of Mycobacterium ulcerans and Other Mycolactone-Producing Mycobacteria from a Common Mycobacterium marinum Progenitor

“…MURD152 is a 2.8-kb DNA fragment deleted from M. ulcerans strain Agy99 (ST17) that spans esxA and esxB, genes encoding key components of the ESX-1 secretion apparatus and virulence factor (4,34). The MURD152 deletion PCR assay confirmed earlier findings that showed that esxA and esxB are absent from M. ulcerans strains from Africa, Australia, and Malaysia but present in other MPM (19,26 (32).…”

“…The recent discovery of MPM that are phenotypically distinct from M. ulcerans in diseased fish and frogs has highlighted the possibility that pMUM is being transferred among different mycobacterial species (19,26). In this report, we show by a systematic genetic approach that all MPM are very closely related to each other and have evolved, not by multiple exchanges of pMUM, but from a common M. marinum progenitor that acquired the plasmid.…”

“…Limited sequence comparisons of hsp65, the 16S rRNA gene, the 16S-23S rRNA gene internal transcribed sequence spacer, and rpoB gene fragments showed that this mycobacterium shared greater than 98% nucleotide identity with M. ulcerans and M. marinum (37). In a subsequent investigation, the frog mycobacterium was shown to contain a version of the M. ulcerans pMUM plasmid and to produce a new mycolactone, mycolactone E (13,19). It was also given the unofficial epithet Mycobacterium liflandii (19).…”

“…In a subsequent investigation, the frog mycobacterium was shown to contain a version of the M. ulcerans pMUM plasmid and to produce a new mycolactone, mycolactone E (13,19). It was also given the unofficial epithet Mycobacterium liflandii (19). In 2005, another new mycobacterium, isolated during an epizootic of mycobac-teriosis from diseased striped bass (Morone saxatilis) in Chesapeake Bay, was also shown to contain IS2404 and IS2606 and to share Ͼ98% nucleotide sequence identity with M. ulcerans, M. marinum, and Mycobacterium shottsii (28).…”

Transfer, stable maintenance and expression of the mycolactone polyketide megasynthase mls genes in a recombination-impaired Mycobacterium marinum

“…It has recently been discovered that mycolactones are produced not only by M. ulcerans but also by a variety of very closely related, pMUM-bearing mycobacteria, collectively referred to as mycolactone-producing mycobacteria (MPM) (Mve-Obiang et al, 2005;Ranger et al, 2006;Yip et al, 2007). Interestingly, different MPM produce mycolactone structural variants that differ in the composition of the acyl side-chain.…”