The galU gene is required for in vivo survival of pseudomonas plecoglossicida in large yellow croaker (Larimichthys crocea)

Disruption of a kasB homolog gene (kasB) causes attenuation of cell invasion and virulence of Nocardia seriolae

Nocardia seriolae is the primary aetiological agent of nocardiosis in fish, which causes mass mortality in freshwater and marine fish. β-ketoacyl-ACP synthase (KAS) is one of the essential enzymes in the synthesis of mycolic acids (MASs) in Mycobacterium spp. and has been chosen as the target for therapeutic intervention in mycobacterial diseases. In the present study, a kasB homologue gene (kasB) was identified in the genome of N. seriolae, and the gene-deficient mutant (ΔkasB) was generated based on a clinical isolate, XSYC-Ns. Compared to the wild-type (WT) strain, the ΔkasB showed a measurably growth defect in vitro but retained the acid-fastness in acid-fast staining. Observation of the cell ultrastructure showed some alterations in the cell wall of the ΔkasB strain. Compared to its original strain, the cell wall lipid layer seemed sparser, and a wider electron-transparent zone was observed in the cell wall of ΔkasB strain. Moreover, the ΔkasB strain showed impaired ability of cell invasion as well as intracellular survival in the cell line originating from the head-kidney of the large yellow croaker (LYC-hK), compared to its original strain. In addition, the deficiency of ΔkasB significantly attenuated the virulence of N. seriolae in largemouth bass. The present study suggested that the ΔkasB gene might be involved in the synthesis of extracellular cell-wall lipids in N. seriolae and play a crucial role in its pathogenicity.

Identification of large yellow croakers (Larimichthys crocea) scavenger receptor genes: Involvement in immune response to Pseudomonas plecoglossicida infection and hypoxia-exposure experiments

Scavenger receptors (SRs) are pattern recognition receptors involved in the innate immune defense against pathogen infection in fish. However, there has not been much research done on teleosts. In this study, 18 members of the SR gene family were found in large yellow croaker. The identification of the SR gene family showed that the protein length of SR members in large yellow croaker were quite different, and most SR genes were distributed in nuclear and endoplasmic. The evolutionary relationship, exon/intron structure and motif analysis revealed that members of the SR gene family were highly conserved. The results of the expression profiles after Pseudomonas plecoglossicida infection and hypoxia-exposure demonstrated that SR members were involved in inflammatory reactions. Especially, COLEC12 and SCARF1 exhibited substantial changes in response to both P. plecoglossicida and hypoxia stress, indicating their possible immunological functions. The result of this study revealed that SR genes played a vital part in the innate immune response of large yellow croaker, and would give important details for a deeper comprehension of the SR gene family's regulation mechanism under various conditions in large yellow croaker.

Pseudomonas plecoglossicida fliP gene affects the immune response of Epinephelus fuscoguttatus ♀×Epinephelus lanceolatus ♂ to infection

Pseudomonas plecoglossicida is a pathogen that causes visceral white spot disease in a variety of teleosts. The protein encoded by fliP gene is involved in the assembly of bacterial flagella, which plays a vital role in bacterial pathogenicity. However, the roles of the fliP gene on the host immune response remain unclear. Here, we compared the pathogenicity of fliP gene-deleted (ΔfliP) strain, fliP gene-complemented (C-ΔfliP) strain and wild-type (NZBD9) strain of P. plecoglossicida to hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂), and explored the impacts of fliP gene on the immune response of hybrid grouper to P. plecoglossicida infection by using RNA-seq. In this study, the grouper in the ΔfliP strain-infected group had a 30% higher survival rate than those in the NZBD9 strain-infected group. In addition, the deletion of fliP gene decreased bacterial load in the spleen, intestine, liver as well as head kidney of hybrid grouper and the tissues damage were weakened. Moreover, the infection of hybrid grouper spleen by the ΔfliP strain induced 1,189 differential expression genes compared with the counterpart infected by NZBD9 strain. KEGG enrichment analysis showed that 9 immune-related pathways, 5 signal transduction pathways, and 3 signaling molecules and interaction pathways were significantly enriched. qRT-PCR analysis revealed that the ΔfliP strain mainly up-regulated the expression of inflammation related genes (IL-6, IL-12, IL-1β, IL-10, CXCL8, CXCL10) and immune regulation related genes (TLR2, P65, MyD88, P85, AKT), but down-regulated the expression of cell death related genes (FoxO1, Bim, PLK2 and LDHA) during infection. Based on the above results, fliP gene contributed to the pathogenicity of P. plecoglossicida to hybrid grouper (E. fuscoguttatus ♀ × E. lanceolatus ♂), deletion of fliP gene promoted the inflammation and immune response of hybrid grouper to P. plecoglossicida infection, which accelerating host clearance of pathogen and reducing tissue damages.

Contribution of GalU to biofilm formation, motility, antibiotic and serum resistance, and pathogenicity of Salmonella Typhimurium

Introduction

Salmonella Typhimurium is the leading cause of foodborne illnesses in China, resulting in major epidemics and economic losses in recent years. Uridine diphosphate-glucose pyrophosphorylase galU plays an important role in thebiosynthesis of the bacterial envelope. Herein, we evaluated the role of galU in S. Typhimurium infection in chicken.

Methods

A galU gene mutant was successfully constructed by red homologous recombination technology, and biological characteristics were studied.

Results

The galU mutant strain had a rough phenotype;was defective in biofilm formation, autoagglutination, and motility; exhibited greater sensitivity to most antibiotics, serum, and egg albumen; and had lowercapacity for adhesion to chicken embryo fibroblasts cell line (DF-1). The galU mutant showed dramatically attenuated pathogenicity in chicken embryos (100,000-fold), BALB/c mice (420-fold), and chicks (100-fold).

Discussion

The results imply that galU is an important virulence factor in the pathogenicity of S. Typhimurium, and it may serve a target for the development of veterinary drugs, providing a theoretical basis for the prevention and control of S. Typhimurium.