Identification and Pathogenicity Analysis of Huaxiibacter chinensis Qf-1 in Mink (Neogale vison)

Abstract

Mink (Neogale vison) is a commercially farmed animal of global importance. However, disease outbreaks during farming not only cause significant economic losses but also substantially increase the risk of zoonotic infections. The identification and characterization of pathogenic bacteria remain a major bottleneck restricting the development of healthy and sustainable mink farming. In this study, an LB medium was used to isolate a pale-white, rod-shaped, Gram-negative bacterial strain, Qf-1, from minks with pneumonia. Based on morphological characteristics, biochemical properties, 16S rRNA gene sequencing, and average nucleotide identity (ANI) analysis, strain Qf-1 was identified as Huaxiibacter chinensis Qf-1. Under laboratory conditions, H. chinensis Qf-1 induced typical pneumonia symptoms in Kunming mice. Furthermore, whole-genome sequencing of H. chinensis Qf-1 revealed its genome to be 4.77 Mb and to contain a single chromosome and one plasmid. The main virulence genes of H. chinensis Qf-1 were primarily associated with flgB, flgC, flgG, aceA, hemL, tssC1, csgD, hofB, ppdD, hcpA, and vgrGA, functioning in motility, biofilm formation, colonization ability, and secretion systems. Our findings contribute to a better understanding of their pathogenic mechanisms, thereby laying a theoretical foundation for further investigation into the complex interactions between gut microbiota and the host.

Keywords: Huaxiibacter chinensis Qf-1; Neogale vison; culturomics; genome; pathogenicity.

Figure 1

Morphological characteristics of Qf-1. (A) Qf-1 colonies on LB culture medium (bar = 1 cm). (B) Gram staining of QF-1 (bar = 10 µm). (C) Morphology of XP-2 observed by SEM (bar = 500 nm). (D) Morphology of XP-2 observed by TEM (bar = 500 nm).

Figure 2

Growth curve and the standard growth curve of Qf-1. (A) The growth curve of Qf-1. (B) The standard growth curve of Qf-1.

Figure 3

Neighbor-joining phylogenetic tree based on 16S rRNA gene sequences. Percentage bootstrap values above 50% (1000 replicates) are shown at branch nodes. Bar = 0.020, substitutions per nucleotide position. Vibrio albus E4404^T was used as an outgroup.

Figure 4

Histopathological observation of lung tissue in Kunming mice infected with H. chinensis Qf-1. Note: Extensive hemorrhage (yellow arrows); mild edema of bronchiolar epithelial cells (red arrows); mild infiltration of granulocytes (black arrows); numerous macrophages in the alveolar spaces (gray arrows); prominent peribronchiolar and perivascular lymphocytic (blue arrows); granulocytic (orange arrows) infiltration forming ring-like patterns; and proliferation of connective tissue (green arrows). The black box indicates the magnified area shown. Bar: (A,C,E,G) = 1000 µm; (B,D,F,H) = 100 µm.

Figure 5

The genome functional annotation of H. chinensis Qf-1 against the GO and KEGG databases (A), the GO annotation of H. chinensis Qf-1; (B) the KEGG annotation of H. chinensis Qf-1.

Figure 6

Circular representation of the H. chinensis Qf-1 genome. From the inside to the outside, the first circle represents the scale; the second circle represents GCSkew; the third circle represents GC content; the fourth and seventh circles represent COGs, to which each CDS belongs; and the fifth and sixth circles represent the positions of CDS, tRNA, and rRNA on the genome.