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This Article Full Text Full Text (PDF) Supplementary data All Versions of this Article: mic.0.027029-0v1 155/6/1923    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Google Scholar Articles by Porter, J. L. Articles by Stinear, T. P. PubMed PubMed Citation Articles by Porter, J. L. Articles by Stinear, T. P. Agricola Articles by Porter, J. L. Articles by Stinear, T. P.

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

Timothy P. Stinear^1,

¹ Department of Microbiology, Monash University, Clayton 3800, Victoria, Australia
² Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, UK
³ School of Chemistry, Monash University, Clayton 3800, Victoria, Australia

The human pathogen Mycobacterium ulcerans produces a polyketide metabolite called mycolactone with potent immunomodulatory activity. M. ulcerans strain Agy99 has a 174 kb plasmid called pMUM001 with three large genes (mlsA1, 51 kb; mlsA2, 7.2 kb; mlsB, 43 kb) that encode type I polyketide synthases (PKS) required for the biosynthesis of mycolactone, as demonstrated by transposon mutagenesis. However, there have been no reports of transfer of the mls locus to another mycobacterium to demonstrate that these genes are sufficient for mycolactone production because in addition to their large size, the mls genes contain a high level of internal sequence repetition, such that the entire 102 kb locus is composed of only 9.5 kb of unique DNA. The combination of their large size and lack of stability during laboratory passage makes them a challenging prospect for transfer to a more rapidly growing and genetically tractable host. Here we describe the construction of two bacterial artificial chromosome Escherichia coli/Mycobacterium shuttle vectors, one based on the pMUM001 origin of replication bearing mlsB, and the other based on the mycobacteriophage L5 integrase, bearing mlsA1 and mlsA2. The combination of these two constructs permitted the two-step transfer of the entire 174 kb pMUM001 plasmid to Mycobacterium marinum, a rapidly growing non-mycolactone-producing mycobacterium that is a close genetic relative of M. ulcerans. To improve the stability of the mls locus in M. marinum, recA was inactivated by insertion of a hygromycin-resistance gene using double-crossover allelic exchange. As expected, the recA mutant displayed increased susceptibility to UV killing and a decreased frequency of homologous recombination. Southern hybridization and RT-PCR confirmed the stable transfer and expression of the mls genes in both wild-type M. marinum and the recA mutant. However, neither mycolactone nor its predicted precursor metabolites were detected in either strain. These experiments show that it is possible to successfully manipulate and stably transfer the large mls genes, but that other bacterial host factors appear to be required to facilitate mycolactone production.

Correspondence
Timothy P. Stinear
tstinear{at}unimelb.edu.au

Present address: Department of Microbiology and Immunology, University of Melbourne, Royal Parade, Parkville 3010, Australia.

Two supplementary figures, showing circular maps of pMUM001 and the E. coli/Mycobacterium BAC shuttle vectors, and ion traces from LC-MS-MS analysis, and two supplementary tables listing oligonucleotides used to construct and test M. marinum M recA and oligonucleotides used to screen for pMUM001, are available with the online version of this paper.