Integrated circuits: how transcriptional silencing and counter-silencing facilitate bacterial evolution

Will, W. Ryan; Navarre, William W.; Fang, Ferric C.

doi:10.1016/j.mib.2014.10.005

Cited by 59 publications

(61 citation statements)

References 76 publications

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“…All of these studies point out that a functional SPI-6 T6SS is expressed during in vivo infection and further suggest that H-NS silencing should be counteracted under these conditions. Derepression of H-NS-silenced genes, known as countersilencing, can occur by competition with sequence-specific DNA binding regulators or by disruption of H-NS nucleoprotein filaments by DNA bending (53,85). A number of transcriptional activators, including PhoP, SlyA, and LeuO, have been shown to antagonize H-NS silencing in E. coli and S. Typhimurium (86)(87)(88)(89)(90)(91).…”

Section: Discussionmentioning

confidence: 99%

H-NS Silencing of the Salmonella Pathogenicity Island 6-Encoded Type VI Secretion System Limits Salmonella enterica Serovar Typhimurium Interbacterial Killing

et al. 2015

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The secretion of bacterial toxin proteins is achieved by dedicated machineries called secretion systems. The type VI secretion system (T6SS) is a widespread versatile machine used for the delivery of protein toxins to both prokaryotic and eukaryotic cells. In Salmonella enterica serovar Typhimurium, the expression of the T6SS genes is activated during macrophage or mouse infection. Here, we show that the T6SS gene cluster is silenced by the histone-like nucleoid structuring H-NS protein using a combination of reporter fusions, electrophoretic mobility shift assays, DNase footprinting, and fluorescence microscopy. We further demonstrate that derepression of the S. Typhimurium T6SS genes induces T6SS-dependent intoxication of competing bacteria. Our results suggest that relieving T6SS H-NS silencing may be used as a sense-and-kill mechanism that will help S. Typhimurium to homogenize and synchronize the microbial population to gain efficiency during infection. During the course of infection, bacteria produce and secrete bacterial toxins. Secretion of these toxin proteins is achieved by dedicated, specialized machineries called secretion systems. The type VI secretion system (T6SS) is required for the virulence of several Gram-negative pathogens. In Vibrio cholerae, the T6SS translocates VgrG1, a toxin that carries a domain responsible for actin cross-linking in eukaryotic cells (1-4). However, the role of the T6SS is not limited to virulence toward eukaryotes; an increasing number of reports demonstrate that the T6SS is also involved in interbacterial intoxication (5-10). With bacteriocins and contact-dependent inhibition (CDI), the T6SS is therefore involved in shaping bacterial communities (11-14) by delivering antibacterial toxins, including murein hydrolases, DNases, and phospholipases, directly into the target recipient bacterial cell (5, 6, 15; for recent reviews see references 14, 16 and 17). The attacker cell is protected from these toxins by the coproduction of cognate proteins that confer immunity (15, 18). The T6SS therefore confers a growth advantage to bacteria in mixed cultures and has been suggested to be important in environmental niches where bacterial competition for nutrients is critical for survival or for the uptake of DNA for transformation and acquisition of new traits (14, 19). However, while the role of the T6SS in interbacterial competition has been evidenced and characterized under laboratory conditions, its role in shaping bacterial communities of the microbiota is not yet clearly elucidated.At the molecular level, the T6SS is assembled from 13 proteins, called core components, that form a transenvelope apparatus anchoring a cytoplasmic tubular structure to the membrane (20-24). Based on structural homologies with bacteriophage tail components, this tubular structure has been proposed to be constituted of an inner tube assembled by stacked hexameric rings of the Hcp protein, resembling the tail tube of bacteriophages, tipped by the VgrG protein (21,(25)(26)(27)). The current model descr...

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Section: Discussionmentioning

confidence: 99%

H-NS Silencing of the Salmonella Pathogenicity Island 6-Encoded Type VI Secretion System Limits Salmonella enterica Serovar Typhimurium Interbacterial Killing

et al. 2015

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“…Thus, widespread repression of transcription by H-NS represents an opportunity to activate transcription of genes in a highly specific manner. This is a common strategy for regulating virulence genes, and is likely to evolve rapidly since many promoter architectures can be accommodated and any DNA-binding protein can activate transcription in this manner [56,57]. Given the wide variety of mechanisms by which H-NS can repress transcription, it is likely that many mechanisms of anti-repression have yet to be discovered.…”

Section: Discussionmentioning

confidence: 99%

H-NS and RNA polymerase: a love–hate relationship?

Landick¹,

Wade²,

Grainger³

2015

Current Opinion in Microbiology

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“…In contrast, many organisms contain several HLPs, suggesting that these proteins have diversified more extensively than any other XS regulators (Supplementary Tables S1 and S4). In fact, in organisms having more than one HLP there is evidence that these proteins have multiple roles, even that of counteracting the repressive role of H-NS (reviewed in Will et al, 2015). For instance, Ler, a transcriptional regulator of enteropathogenic and enterohemorrhagic E. coli pathovars virulence genes, belongs to the HLP family and has been shown to overcome H-NS repression in optimal inducing conditions by competing for binding sites in the promoter regions (Winardhi et al, 2014).…”

Section: H-ns-like Proteins (Hlps)mentioning

confidence: 99%