The opportunistic pathogenStenotrophomonas maltophiliautilizes a type IV secretion system for interbacterial killing

AbstractBacterial type IV secretion systems (T4SS) are a highly diversified but evolutionarily related family of macromolecule transporters that can secrete proteins and DNA into the extracellular medium or into target cells. They have been long known to play a fundamental role in bacterial conjugation and virulence of several species. It was recently shown that a subtype of T4SS harboured by the plant pathogenic bacteriumXanthomonas citritransfers toxins into other bacteria cells resulting in cell death. In this study, we show that a similar T4SS from the multi-drug-resistant global opportunistic pathogenStenotrophomonas maltophiliais proficient in killing competitor bacterial species. T4SS-dependent duelling betweenS. maltophiliaandX. citriwas observed by time-lapse fluorescence microscopy. A bioinformatic search of theS. maltophiliaK279a genome for proteins containing a C-terminal domain (XVIPCD) conserved inX. citriT4SS effectors identified eleven putative effectors secreted by theS. maltophiliaT4SS. Six of these effectors have no recognizable domain except for the XVIPCD. We selected one of these new effectors (Smlt3024) and its cognate inhibitor (Smlt3025) for further characterization and confirmed that Smlt3024 is indeed secreted in a T4SS-dependent manner byS. maltophiliawhen in contact with a target bacterial species. Expression of Smlt3024 in the periplasm ofE. coliresulted in greatly reduced growth rate and cell size, which could be counteracted by co-expression with its cognate periplasmic inhibitor, Smlt3025. This work expands our current knowledge about the diverse function of T4SSs subtypes and increases the panel of effectors known to be involved in T4SS-mediated interbacterial competition. Further elucidation of the mechanism of these antibacterial proteins could lead to the discovery of new antibacterial targets. The study also adds information about the molecular mechanisms possibly contributing to the establishment ofS. maltophiliain different biotic and abiotic surfaces in both clinical and environmental settings.Author SummaryCompetition between microorganisms for nutrients and space determines which species will emerge and dominate or be eradicated from a specific habitat. Bacteria use a series of mechanisms to kill or prevent multiplication of competitor species. Recently, it was reported that a subtype of type IV secretion system (T4SS) works as a weapon to kill competitor bacterial species. In this study, we show that an important human opportunistic pathogen,Stenotrophomonas maltophilia, harbours a T4SS that promotes killing of competitor species. We also identified a series of new toxic proteins secreted byS. maltophiliavia its T4SS to poison competitor species. We showed that two different bacterial species that harbour a bacteria-killing T4SS can kill each other; most likely due to differences in effector-immunity protein pairs. This work expands our current knowledge about the bacterial arsenal used in competitions with other species and expands the repertoire of antibacterial ammunition fired by T4SSs. In addition, the work contributes with knowledge on the possible mechanisms used byS. maltophiliato establish communities in different biotic and abiotic surfaces in both clinical and environmental settings.

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Effectors of the Stenotrophomonas maltophilia Type IV Secretion System Mediate Killing of Clinical Isolates of Pseudomonas aeruginosa

mBio ◽

10.1128/mbio.01502-21 ◽

2021 ◽

Author(s):

Megan Y. Nas ◽

Jeffrey Gabell ◽

Nicholas P. Cianciotto

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Stenotrophomonas Maltophilia ◽

Opportunistic Pathogen ◽

Lung Infection ◽

Secretion System ◽

Type Iv Secretion ◽

Type Iv Secretion System ◽

Content Type ◽

Type Iv

S. maltophilia is an increasingly important opportunistic pathogen. Inherently resistant to many antibiotics, S. maltophilia is often associated with lung infection, being, among other things, a complicating factor in cystic fibrosis patients.

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The opportunistic pathogen Stenotrophomonas maltophilia utilizes a type IV secretion system for interbacterial killing

PLoS Pathogens ◽

10.1371/journal.ppat.1007651 ◽

2019 ◽

Vol 15 (9) ◽

pp. e1007651 ◽

Cited By ~ 9

Author(s):

Ethel Bayer-Santos ◽

William Cenens ◽

Bruno Yasui Matsuyama ◽

Gabriel Umaji Oka ◽

Giancarlo Di Sessa ◽

...

Keyword(s):

Stenotrophomonas Maltophilia ◽

Opportunistic Pathogen ◽

Secretion System ◽

Type Iv Secretion ◽

Type Iv Secretion System ◽

Type Iv

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Brucella suppress innate immunity by down-regulating STING expression in macrophages

10.1101/2019.12.31.891051 ◽

2020 ◽

Author(s):

Mike Khan ◽

Jerome S. Harms ◽

Yiping Liu ◽

Jens Eickhoff ◽

Jin Wen Tan ◽

...

Keyword(s):

Innate Immunity ◽

Damage Control ◽

Bacterial Species ◽

Secretion System ◽

Type Iv Secretion ◽

Innate Immune ◽

Type Iv Secretion System ◽

Chronic Infections ◽

Type Iv ◽

The Impact

AbstractBrucellosis, caused by Brucella bacteria species, remains the most prevalent zoonotic disease worldwide. Brucella establish chronic infections within host macrophages despite triggering cytosolic innate immune sensors, including Stimulator of Interferon Genes (STING), which potentially limit infection. In this study, STING was required for control of chronic Brucella infection in vivo. However, early during infection, Brucella down-regulated STING mRNA and protein. Down-regulation occurred post-transcriptionally, required live bacteria, the Brucella type IV secretion system, and was independent of host IRE1-RNase activity. Rather, Brucella induced a STING-targeting microRNA, miR-24-2. Furthermore, STING downregulation was inhibited by miR-24 anti-miRs and in mirn23a locus-deficient macrophages. Failure to suppress STING expression in mirn23a−/− macrophages correlated with diminished Brucella replication, and was rescued by exogenous miR-24. Anti-miR-24 potently suppressed replication in wild type, but much less in STING−/− macrophages, suggesting most of the impact of miR-24 induction on replication occurred via STING suppression. In summary, Brucella sabotages innate immunity by miR-24-dependent suppression of STING expression; post-STING activation “damage control” via targeted STING destruction may enable establishment of chronic infection.Author summaryCytosolic pattern recognition receptors, such as the nucleotide-activated STING molecule, play a critical role in the innate immune system by detecting the presence of intracellular invaders. Brucella bacterial species establish chronic infections in macrophages despite initially activating STING. STING does participate in the control of Brucella infection, as mice or cells lacking STING show a higher burden of Brucella infection. However, we have found that early following infection, Brucella upregulates a microRNA, miR-24, that targets the STING messenger RNA, resulting in lower STING levels. Dead bacteria or bacteria lacking a functional type IV secretion system were defective at upregulating miR-24 and STING suppression, suggesting an active bacteria-driven process. Failure to upregulate miR-24 and suppress STING greatly compromised the capacity for Brucella to replicate inside macrophages. Thus, although Brucella initially activate STING during infection, the ensuing STING downregulation serves as a “damage control” mechanism, enabling intracellular infection. Viruses have long been known to target immune sensors such as STING. Our results indicate that intracellular bacterial pathogens also directly target innate immune receptors to enhance their infectious success.

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Type IV Secretion System Is Not Involved in Infection Process in Citrus

International Journal of Microbiology ◽

10.1155/2014/763575 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 10

Author(s):

Tiago Rinaldi Jacob ◽

Marcelo Luiz de Laia ◽

Leandro Marcio Moreira ◽

Janaína Fernandes Gonçalves ◽

Flavia Maria de Souza Carvalho ◽

...

Keyword(s):

Cell Envelope ◽

Positive Control ◽

Secretion System ◽

Infection Process ◽

Type Iv Secretion ◽

Target Cells ◽

Type Iv Secretion System ◽

In Planta ◽

Type Iv

The type IV secretion system (T4SS) is used by Gram-negative bacteria to translocate protein and DNA substrates across the cell envelope and into target cells.Xanthomonas citrisubsp.citricontains two copies of the T4SS, one in the chromosome and the other is plasmid-encoded. To understand the conditions that induce expression of the T4SS inXcc, we analyzed,in vitroandin planta, the expression of 18 ORFs from the T4SS and 7 hypothetical flanking genes by RT-qPCR. As a positive control, we also evaluated the expression of 29 ORFs from the type III secretion system (T3SS), since these genes are known to be expressed during plant infection condition, but not necessarily in standard culture medium. From the 29 T3SS genes analyzed by qPCR, onlyhrpAwas downregulated at 72 h after inoculation. All genes associated with the T4SS were downregulated onCitrusleaves 72 h after inoculation. Our results showed that unlike the T3SS, the T4SS is not induced during the infection process.

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The Impact of Bartonella VirB/VirD4 Type IV Secretion System Effectors on Eukaryotic Host Cells

Frontiers in Microbiology ◽

10.3389/fmicb.2021.762582 ◽

2021 ◽

Vol 12 ◽

Author(s):

Katja Fromm ◽

Christoph Dehio

Keyword(s):

Current Knowledge ◽

Secretion System ◽

Effector Proteins ◽

Type Iv Secretion ◽

Host Cells ◽

Type Iv Secretion System ◽

Type Iv ◽

Wide Range ◽

Host Signaling ◽

The Impact

Bartonella spp. are facultative intracellular pathogens that infect a wide range of mammalian hosts including humans. The VirB/VirD4 type IV secretion system (T4SS) is a key virulence factor utilized to translocate Bartonella effector proteins (Beps) into host cells in order to subvert their functions. Crucial for effector translocation is the C-terminal Bep intracellular delivery (BID) domain that together with a positively charged tail sequence forms a bipartite translocation signal. Multiple BID domains also evolved secondary effector functions within host cells. The majority of Beps possess an N-terminal filamentation induced by cAMP (FIC) domain and a central connecting oligonucleotide binding (OB) fold. FIC domains typically mediate AMPylation or related post-translational modifications of target proteins. Some Beps harbor other functional modules, such as tandem-repeated tyrosine-phosphorylation (EPIYA-related) motifs. Within host cells the EPIYA-related motifs are phosphorylated, which facilitates the interaction with host signaling proteins. In this review, we will summarize our current knowledge on the molecular functions of the different domains present in Beps and highlight examples of Bep-dependent host cell modulation.

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Inhibition of Type IV Secretion Activity and Growth of Helicobacter pylori by Cisplatin and Other Platinum Complexes

Frontiers in Cellular and Infection Microbiology ◽

10.3389/fcimb.2020.602958 ◽

2020 ◽

Vol 10 ◽

Author(s):

Clara Lettl ◽

Franziska Schindele ◽

Giambattista Testolin ◽

Alexander Bär ◽

Tobias Rehm ◽

...

Keyword(s):

Helicobacter Pylori ◽

Dna Binding ◽

Platinum Complexes ◽

Secretion System ◽

Type Iv Secretion ◽

Growth Media ◽

Target Cells ◽

Type Iv Secretion System ◽

Type Iv ◽

H Pylori

Type IV secretion systems are protein secretion machineries that are frequently used by pathogenic bacteria to inject their virulence factors into target cells of their respective hosts. In the case of the human gastric pathogen Helicobacter pylori, the cytotoxin-associated gene (Cag) type IV secretion system is considered a major cause for severe disease, such as gastric cancer, and thus constitutes an attractive target for specific treatment options against H. pylori infections. Here, we have used a Cag type IV secretion reporter assay for screening a repurposing compound library for inhibitors targeting this system. We found that the antitumor agent cisplatin, a platinum coordination complex that kills target cells by formation of DNA crosslinks, is a potent inhibitor of the Cag type IV secretion system. Strikingly, we found that this inhibitory activity of cisplatin depends on a ligand exchange reaction which incorporates a solvent molecule (dimethylsulfoxide) into the complex, a modification which is known to be deleterious for DNA crosslinking, and for its anticancer activity. We extended our analysis to several analogous platinum complexes containing N-heterocyclic carbene, as well as DMSO or other ligands, and found varying inhibitory activities toward the Cag system which were not congruent with their DNA-binding properties, suggesting that protein interactions may cause the inhibitory effect. Inhibition experiments under varying conditions revealed effects on adherence and bacterial viability as well, and showed that the type IV secretion-inhibitory capacity of platinum complexes can be inactivated by sulfur-containing reagents and in complex bacterial growth media. Taken together, our results demonstrate DNA binding-independent inhibitory effects of cisplatin and other platinum complexes against different H. pylori processes including type IV secretion.

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Members of a Legionella pneumophila Family of Proteins with ExoU (Phospholipase A) Active Sites Are Translocated to Target Cells

Infection and Immunity ◽

10.1128/iai.02060-05 ◽

2006 ◽

Vol 74 (6) ◽

pp. 3597-3606 ◽

Cited By ~ 83

Author(s):

Susan M. VanRheenen ◽

Zhao-Qing Luo ◽

Tamara O'Connor ◽

Ralph R. Isberg

Keyword(s):

Legionella Pneumophila ◽

Secretory Pathway ◽

Secretion System ◽

Type Iv Secretion ◽

Phospholipase A ◽

Target Cells ◽

Type Iv Secretion System ◽

Type Iv ◽

System A ◽

Translocated Proteins

ABSTRACT Legionella pneumophila replicates within alveolar macrophages, causing a severe pneumonia termed Legionnaires' disease. The bacterium resides within a vacuole that escapes immediate transport to the host lysosome. Instead, the vacuole interacts with the early secretory pathway to establish an environment suitable for rapid multiplication. A type IV secretion system is central to the pathogenicity of the bacterium, and many protein substrates that are translocated by this system to the host cell have been identified. One of these, VipD, was found to interrupt the late secretory pathway when overproduced in Saccharomyces cerevisiae. We independently identified VipD in a previous study and have further characterized this protein as well as its three paralogs. The vipD gene belongs to a family of L. pneumophila open reading frames that are predicted to contain a phospholipase A domain with sequence similarity to the type III-secreted toxin ExoU from Pseudomonas aeruginosa. Similarly to other known translocated proteins of L. pneumophila, VipD is strongly induced in early stationary phase, a time when the bacterium is most virulent. Detergent extraction studies of infected macrophages confirm that VipD is translocated into host cells via the type IV secretion system. A second assay for translocation revealed that two paralogs of VipD, VpdA and VpdB, also have translocation signals recognized by the type IV system. A strain lacking VipD and its three paralogs grew at wild-type rates in murine macrophages, although secondary mutations that cause growth defects in strains lacking VipD accumulate. The quadruple mutant displayed a growth advantage in the amoebal host Dictyostelium discoideum, indicating that the protein family may modulate intracellular growth in a complex fashion. VipD is mildly toxic when overproduced in eukaryotic cells, and the toxicity is partially dependent on the putative phospholipase active site. VipD and its paralogs therefore define a family of translocated proteins that may assist in the establishment of a vacuole suitable for bacterial replication through functioning as a phospholipase.

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