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This Article Full Text (Papers in Press[PDF]) 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 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 Citing Articles via Google Scholar Google Scholar Articles by Porter, J. L. Articles by Stinear, T. P. Search for Related Content 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

¹ Monash University;
² University of Cambridge

ABSTRACT

The human pathogen Mycobacterium ulcerans produces a polyketide metabolite called mycolactone with potent immunomodulatory activity. M. ulcerans strain Agy99 has a 173 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 E. 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 & mlsA2. The combination of these two constructs permitted the two-step transfer of the entire 173 kb pMUM001 plasmid to Mycobacterium marinum; a rapid-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 delta recA mutant displayed increased susceptibility to UV killing and a decreased frequency of homologous recombination. Southern hybridization and reverse transcriptase 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 required to facilitate mycolactone production.

³ E-mail: tim.stinear{at}med.monash.edu.au