Riemerella anatipestifer UvrC is required for iron utilization, biofilm formation and virulence.

UvrC is a subunit of excinuclease ABC, which mediates nucleotide excision repair (NER) in bacteria. Our previous studies showed that transposon Tn4531 insertion in the UvrC encoding gene Riean_1413 results in reduced biofilm formation by Riemerella anatipestifer strain CH3 and attenuates virulence of strain YZb1. In this study, whether R. anatipestifer UvrC has some biological functions other than NER was investigated. Firstly, the uvrC of R. anatipestifer strain Yb2 was in-frame deleted by homologous recombination, generating deletion mutant ΔuvrC, and its complemented strain cΔuvrC was constructed based on Escherichia coli - R. anatipestifer shuttle plasmid pRES. Compared to the wild-type (WT) R. anatipestifer strain Yb2, uvrC deleted mutant ΔuvrC significantly reduced biofilm formation, tolerance to H2O2- and HOCl-induced oxidative stress, iron utilization, and adhesion to and invasion of duck embryonic hepatocytes, but not its growth curve and proteolytic activity. In addition, animal experiments showed that the LD50 value of ΔuvrC in ducklings was about 13-fold higher than that of the WT, and the bacterial loads in ΔuvrC infected ducklings were significantly lower than those in Yb2-infected ducklings, indicating uvrC deletion in R. anatipestifer attenuated virulence. Taken together, the results of this study indicate that R. anatipestifer UvrC is required for iron utilization, biofilm formation, oxidative stress tolerance and virulence of strain Yb2, demonstrating multiple functions of UvrC.RESEARCH HIGHLIGHTSDeletion of uvrC in R. anatipestfer Yb2 significantly reduced its biofilm formation.uvrC deletion led to reduced tolerance to H2O2- and HOCl-induced oxidative stress.The iron utilization of uvrC deleted mutant was significantly reduced.The uvrC deletion in R. anatipestifer Yb2 attenuated its virulence.

DEAD Box Protein DhR1 Is a Global Regulator Involved in the Bacterial Fitness and Virulence of Riemerella anatipestifer.

DEAD box proteins perform diverse cellular functions in bacteria. Our group previously reported that the transposon Tn4531 insertion in Riean_0395 (designated dhR1), which encodes a putative DEAD box helicase, attenuated the virulence of R. anatipestifer strain YZb1. Here, we show that, compared to the wild-type (WT) R. anatipestifer strain Yb2, the growth or survival of the ΔdhR1 mutant in tryptic soy broth (TSB) was significantly decreased in response to cold, pH, osmotic stress, ethanol, Triton X-100, and oxidative stress, and the dhR1 deletion significantly reduced biofilm formation and the adhesion capacity to Vero cells, whereas the growth of ΔdhR1 was less impaired in iron-limited TSB. Moreover, the virulence of ΔdhR1 in ducklings was attenuated by about 80-fold, compared to the WT. In addition, a transcriptome analysis showed that the dhR1 deletion in the strain Yb2 affected the expression of 58 upregulated genes and 98 downregulated genes that are responsible for various functions. Overall, our work reveals that the deletion of DhR1 results in a broad effect on the bacterial fitness, biofilm formation, iron utilization, and virulence of R. anatipestifer, which makes it a global regulator. IMPORTANCE R. anatipestifer infection has been a continued and serious problem in many duck farms, but little is known about the mechanism underlying the pathogenesis of R. anatipestifer and how R. anatipestifer adapts to the external environment and thereby persists in duck farms. The results of this study demonstrate that the DEAD box protein DhR1 is required for the tolerance of R. anatipestifer to cold, pH, and other stresses, and it is also necessary for biofilm formation, iron utilization, and virulence in ducklings, demonstrating multiple functions of DhR1.

MicroRNA-223 Inhibits Soybean Glycinin- and ß-Conglycinin-Induced Apoptosis of IPEC-J2 Cells by Targeting NLRP-3 in the IEL/IPEC-J2 Co-culture System.

The apoptosis of intestinal porcine epithelial cells induced by soybean antigen protein allergy is one of the most important mechanisms responsible for enteritis. MicroRNAs (miRNAs) affect the cellular and physiological functions of all multicellular organisms. We hypothesize that microRNA-223 inhibits soybean glycinin- and ß-conglycinin-induced apoptosis of intestinal porcine enterocytes (IPEC-J2) by targeting the NLR family pyrin domain containing 3 (NLRP-3). Using the intestinal interepithelial lymphocyte (IEL)/IPEC-J2 co-culture system as an in vitro model, we investigate the role of microRNA-223 in the regulation of soybean glycinin- and ß-conglycinin-induced apoptosis. In co-cultured IEL/IPEC-J2 cells incubated with glycinin or ß-conglycinin, microRNA-223 decreased NLRP-3, ASC, caspase-1, caspase-3, FAS, BCL-2, and APAF-1 expressions in IPEC-J2 cells; decreased cytokine and cyclooxygenase-2 levels; significantly increased cell activity; and inhibited apoptosis. These data supported a novel antiallergic mechanism to mitigate the sensitization of soybean antigenic protein, which involves the upregulation of microRNA-223-targeting NLRP-3.

PaR1 secreted by the type IX secretion system is a protective antigen of Riemerella anatipestifer.

Riemerella anatipestifer mainly infects domestic ducks, geese, turkeys, and other birds, and causes considerable economic losses to the global duck industry. Previous studies have shown that concentrated cell-free culture filtrates of R. anatipestifer induce highly significant protection against homologous challenge. In this study, 12 immunogenic proteins were identified in the culture supernatant of R. anatipestifer strain Yb2 with immunoproteomic analysis. Of these, three immunogenic proteins, AS87_RS06600 (designated "PaR1" in this study), AS87_RS09020, and AS87_RS09965, which appeared in more than three spots on the western-blotted membrane, were expressed in Escherichia coli and purified. Animal experiments showed that the recombinant PaR1 (rPaR1) protein protected 41.67% of immunized ducklings against challenge with virulent Yb2, whereas rAS87_RS09020 or rAS87_RS09965 did not, and that ducklings immunized once with rPaR1 were 20, 40, and 0% protected from challenge with R. anatipestifer strains WJ4 (serotype 1), Yb2 (serotype 2), and HXb2 (serotype 10), respectively. In addition, rPaR1 immunized rabbit serum showed bactericidal activity against strain Yb2 at a titer of 1:8. These results indicate that rPaR1 of strain Yb2 protects against homologous challenge. Amino acid homology analysis show that PaR1 is a non-serotype-specific protein among different R. anatipestifer serotypes. Furthermore, PaR1 is mainly secreted outside the cell through the T9SS. Overall, our results demonstrate that R. anatipestifer PaR1 is a non-serotype-specific protective protein secreted by the T9SS.