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In vivo expression technology identifies a type VI secretion system locus in Burkholderia pseudomallei that is induced upon invasion of macrophages

Gil Shalom

Unit of Infection and Immunity, School of Medicine and Biomedical Sciences, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, UK

Correspondence
Mark S. Thomas
m.s.thomas{at}shef.ac.uk

The Gram-negative proteobacterium Burkholderia pseudomallei can survive and multiply within a variety of eukaryotic cells, including macrophages. This property is believed to be important for its ability to cause the disease melioidosis in a wide range of animal species, including humans. To identify determinants that are important for the ability of B. pseudomallei to survive within macrophages, in vivo expression technology (IVET) was employed. Several putative macrophage-inducible genes were identified that are likely to contribute to the virulence of B. pseudomallei, including three genes (tssH-5, tssI-5 and tssM-5) located within the same type VI secretion system cluster (tss-5), mntH, encoding a natural resistance-associated macrophage protein (NRAMP)-like manganese ion transporter, and a haem acquisition gene, bhuT. The macrophage-inducibility of the tss-5 gene cluster was confirmed by reporter gene analysis. Construction of tssH-5 and bhuT null mutants indicated that expression of the tss-5 unit and the bhu operon were not required for intramacrophage survival. A further five tss units were identified within the B. pseudomallei genome that, together with tss-5, account for approximately 2.3 % of the total genome size. The presence of six type VI secretion systems in this organism is likely to be an important factor in making this bacterium such a versatile pathogen.

Present address: Division of Microbial Diseases, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.

Supplementary material showing the organisation of tss units within proteobacterial genomes, the core components of the tss units, the tss-associated genes and a standardized nomenclature for T6SS is available with the online version of this paper.