Hcp2, a Secreted Protein of the Phytopathogen Pseudomonas syringae pv. Tomato DC3000, Is Required for Fitness for Competition against Bacteria and Yeasts

Abstract

dWhen analyzing the secretome of the plant pathogen Pseudomonas syringae pv. tomato DC3000, we identified hemolysin-coregulated protein (Hcp) as one of the secreted proteins. Hcp is assumed to be an extracellular component of the type VI secretion system (T6SS). Two copies of hcp genes are present in the P. syringae pv. tomato DC3000 genome, hcp1 (PSPTO_2539) and hcp2 (PSPTO_5435). We studied the expression patterns of the hcp genes and tested the fitness of hcp knockout mutants in host plant colonization and in intermicrobial competition. We found that the hcp2 gene is expressed most actively at the stationary growth phase and that the Hcp2 protein is secreted via the T6SS and appears in the culture medium as covalently linked dimers. Expression of hcp2 is not induced in planta and does not contribute to virulence in or colonization of tomato or Arabidopsis plants. Instead, hcp2 is required for survival in competition with enterobacteria and yeasts, and its function is associated with the suppression of the growth of these competitors. This is the first report on bacterial T6SS-associated genes functioning in competition with yeast. Our results suggest that the T6SS of P. syringae may play an important role in bacterial fitness, allowing this plant pathogen to survive under conditions where it has to compete with other microorganisms for resources.

Comparative Secretome Analysis of Ralstonia solanacearum Type 3 Secretion-Associated Mutants Reveals a Fine Control of Effector Delivery, Essential for Bacterial Pathogenicity

“…We also showed with Western blot experiments that the non-detection of some Rips using MS is not because of a non-secretion in our experimental conditions, but is because of the MS detection threshold. Detection of 60% of the R. solanacearum GMI1000 known effectors (43 out of 72 (11)) is satisfactory compared with other T3-secretome studies (51)(52)(53)(54)(55) and considering that several Rip effectors may certainly be low-abundant proteins produced at the host cell contact. We observed a direct correlation between rip gene transcription and the quantitative detection of the corresponding proteins through MS analysis.…”

Type VI secretion system effectors: poisons with a purpose

“…The phyllosphere and the rhizosphere both represent habitats colonized by diverse bacterial species that are often found clustered together 120,121 . The plant pathogen and leaf surface colonizer P. syringae DC3000 tomato has two T6SSs, one of which has been shown to be important for bacterial antagonism in vitro 49,122 . T6SS gene clusters are also common among species from the plant-associated genera Erwinia , Pantoea, and Pectobacterium , and hcp and vrgG genes in P. atrosepticum are induced by potato stem extract 123,124 .…”

Draft Genome Sequence of Pseudomonas sp. LS-2, Isolated from a Diseased Gastrodia elata Plant

“…The NCBI Prokaryotic Genome Annotation Pipeline (7) was used for genome annotation and identified 6,258 coding sequences, 67 RNA genes, and 286 pseudogenes in the strain’s genome. The genome of strain LS-2 harbored 96 potential virulence factors implicated in bacterium-plant interactions, such as flagella (8), the type III secretion system (T3SS) (9), type VI secretion system (T6SS) (8), and several effectors, like the hypersensitive response and pathogenicity (hrp) effector of T3SS (8) and hemolysin-coregulated protein (hcp) effectors of T6SS (10). …”