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Riemerella anatipestifer Type IX Secretion System Is Required for Virulence and Gelatinase Secretion.

ABSTRACT: Riemerella anatipestifer (RA), a major causative agent of septicemia anserum exsudativa in domesticated ducklings, has a protein secretion system known as the type IX secretion system (T9SS). It is unknown whether the T9SS contributes to the virulence of RA through secretion of factors associated with pathogenesis. To answer this question, we constructed an RA mutant deficient in sprT, which encodes a core protein of the T9SS. Deletion of sprT yielded cells that failed to digest gelatin, an effect that was rescued via complementation by a plasmid encoding wild-type sprT. Complement-mediated killing was significantly increased in the deletion mutant, suggesting that proteins secreted by the T9SS are necessary for complement evasion in RA. Liquid chromatography-tandem mass spectrometry analysis revealed that RAYM_01812 and RAYM_04099 proteins containing a subtilisin-like serine protease domain and exhibiting extracellular gelatinase activity were secreted by the T9SS. Animal experiments demonstrated that the virulence of mutant strain ?sprT strain was attenuated by 42,000-fold relative to wild-type RA-YM. Immunization with the ?sprT protected ducks from challenge with RA-YM, suggesting that the former can be used as a live attenuated vaccine. These results indicate that the T9SS is functional in RA and contributes to its virulence by exporting key proteins. In addition, subtilisin-like serine proteases which are important virulence factors that interact with complement proteins may enable RA to evade immune surveillance in the avian innate immune system.

SUBMITTER: Guo Y

PROVIDER: S-EPMC5742166 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Riemerella anatipestifer Type IX Secretion System Is Required for Virulence and Gelatinase Secretion.

Guo Yunqing Y Hu Di D Guo Jie J Wang Tao T Xiao Yuncai Y Wang Xiliang X Li Shaowen S Liu Mei M Li Zili Z Bi Dingren D Zhou Zutao Z

Frontiers in microbiology 20171219

Riemerella anatipestifer (RA), a major causative agent of septicemia anserum exsudativa in domesticated ducklings, has a protein secretion system known as the type IX secretion system (T9SS). It is unknown whether the T9SS contributes to the virulence of RA through secretion of factors associated with pathogenesis. To answer this question, we constructed an RA mutant deficient in sprT, which encodes a core protein of the T9SS. Deletion of sprT yielded cells that failed to di ...[more]

PMID: 29312236

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Project description:Riemerella anatipestifer is a major bacterial pathogen that causes septicemic and exudative diseases in domestic ducks. In our previous study, we found that deletion of the AS87_01735 gene significantly decreased the bacterial virulence of R. anatipestifer strain Yb2 (mutant RA625). The AS87_01735 gene was predicted to encode a nicotinamidase (PncA), a key enzyme that catalyzes the conversion of nicotinamide to nicotinic acid, which is an important reaction in the NAD(+) salvage pathway. In this study, the AS87_01735 gene was expressed and identified as the PncA-encoding gene, using an enzymatic assay. Western blot analysis demonstrated that R. anatipestifer PncA was localized to the cytoplasm. The mutant strain RA625 (named Yb2?pncA in this study) showed a similar growth rate but decreased NAD(+) quantities in both the exponential and stationary phases in tryptic soy broth culture, compared with the wild-type strain Yb2. In addition, Yb2?pncA-infected ducks showed much lower bacterial loads in their blood, and no visible histological changes were observed in the heart, liver, and spleen. Furthermore, Yb2?pncA immunization of ducks conferred effective protection against challenge with the virulent wild-type strain Yb2. Our results suggest that the R. anatipestifer AS87_01735 gene encodes PncA, which is an important virulence factor, and that the Yb2?pncA mutant can be used as a novel live vaccine candidate.Riemerella anatipestifer is reported worldwide as a cause of septicemic and exudative diseases of domestic ducks. The pncA gene encodes a nicotinamidase (PncA), a key enzyme that catalyzes the conversion of nicotinamide to nicotinic acid, which is an important reaction in the NAD(+) salvage pathway. In this study, we identified and characterized the pncA-homologous gene AS87_01735 in R. anatipestifer strain Yb2. R. anatipestifer PncA is a cytoplasmic protein that possesses similar PncA activity, compared with other organisms. Generation of the pncA mutant Yb2?pncA led to a decrease in the NAD(+) content, which was associated with decreased capacity for invasion and attenuated virulence in ducks. Furthermore, Yb2?pncA immunization of ducks conferred effective protection against challenge with the virulent wild-type strain Yb2. Altogether, these results suggest that PncA contributes to the virulence of R. anatipestifer and that the Yb2?pncA mutant can be used as a novel live vaccine candidate.

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Riemerella anatipestifer Type IX Secretion System Is Required for Virulence and Gelatinase Secretion.

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<i>Riemerella anatipestifer</i> Type IX Secretion System Is Required for Virulence and Gelatinase Secretion.

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