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

Abstract

In vivo expression technology identifies a type VI secretion system locus in Burkholderia pseudomallei that is induced upon invasion of macrophages 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. INTRODUCTIONMelioidosis is the name given to any infection caused by Burkholderia pseudomallei, a saprophytic, Gram-negative bacillus found in wet soil and pooled water, particularly in south-east Asia and northern Australia (White, 2003). It is principally acquired following inoculation of lesions in the skin by contaminated soil and water, with the highest incidence of the disease occurring during the rainy and monsoon seasons (Dance, 1991;White, 2003). Another important route of infection is inhalation of contaminated particles. The clinical spectrum of melioidosis ranges from an acute fulminant septicaemia to chronic localized infections, often affecting the lung, and is usually characterized by abscess formation. No vaccines are available, and antibiotic therapy is problematic due to the intrinsic high resistance of B. pseudomallei to many antibiotics. The overall mortality of melioidosis patients is 50 % (White, 2003).Certain features of melioidosis suggest that B. pseudomallei is a facultative intracellular pathogen. These include the occurrence of long periods of latency (a recent case report suggests this can be as long as 62 years), relapses due to recrudescence of a persistent primary infection, and the activation of a cellular immune response during melioidosis (Chaowagul et al., 1993;Ngauy et al., 2005). Consistent with this, B. pseudomallei has been shown to survive and multiply within non-phagocytic cells, macrophages and free-living amoebae (Pruksachartvuthi et al., 1990;Jones et a...

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies

“…The haem acquisition system of Burkholderia cenocepacia is reported to be similar to the huvA-hmuSTUV system of Burkholderia pseudomallei (Shalom et al, 2007), with an operon comprising five genes bhuRSTUV predicted to encode the outer membrane haem receptor, a shuttle protein and components of the haem permease (Thomas, 2007). We have reported the uptake of haemin by Burkholderia cenocepacia in the absence of siderophore secretion, confirming the ability of these pathogens to exploit this host iron source in the CF lung (Tyrrell et al, 2015).…”

Quantification of type VI secretion system activity in macrophages infected with Burkholderia cenocepacia

“…1a). The predicted functions of the T6SS genes are listed in Table S2, and whenever possible the genes are named according to the proposed standard nomenclature for T6SS core components, tss (for T6SS gene) or tag (T6SS-associated gene) (Shalom et al, 2007). Each of the genes in the T6SS cluster was systematically deleted in B. cenocepacia atsR (DatsR) and the mutants were investigated for T6SS-related phenotypes.…”

Suppression of Host Innate Immune Response by Burkholderia pseudomallei through the Virulence Factor TssM

“…One of these loci designated the Burkholderia secretion apparatus (bsa) gene cluster shares homology with the Salmonella typhimurium inv/spa/prg T3SS and is required for cellular invasion and escape from endocytic vesicles (26). This bacterium also possesses six type VI secretion system (T6SS) clusters, and the T6SS-5 has been reported to be important for the invasion of macrophages (27). Several lines of experimental evidence suggest that B. pseudomallei is able to modulate the innate immune response.…”