A deep-sea pathogenic Bacillus subtilis isolate employs different strategies to escape the killing of teleost and murine complements

• Published in: Developmental and comparative immunology Vol. 119; p. 104037
• Main Authors: Gu, Han-jie, Li, Mo-fei, Sun, Li
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.06.2021; Elsevier Science Ltd
• Subjects: Animals; Bacillaceae Infections - blood; Bacillaceae Infections - immunology; Bacillaceae Infections - microbiology; Bacillus subtilis; Bacillus subtilis - immunology; Bacillus subtilis - isolation & purification; Bacillus subtilis - pathogenicity; Blotting, Western; Cell walls; Chemotactic response; Complement; Complement activation; Complement component C3; Complement system; Complement System Proteins - immunology; Deep sea; Deep sea environments; Enzyme-Linked Immunosorbent Assay; Fish Diseases - immunology; Fish Diseases - microbiology; Flounder - blood; Flounder - immunology; Flounder - microbiology; Host-Pathogen Interactions - immunology; Hydrothermal Vents - microbiology; Immune evasion; Immune Evasion - immunology; Lysozyme; Mice; Mice, Inbred BALB C; Phagocytes; RAW 264.7 Cells; Serum resistance; Virulence - immunology; Complement activation; Serum resistance; Immune evasion; Bacillus subtilis
• ISSN: 0145-305X; 1879-0089
• DOI: 10.1016/j.dci.2021.104037

Bacillus subtilis subsp. subtilis G7 was isolated from a deep-sea hydrothermal vent and is pathogenic to pathogenic to fish (Japanese flounder) and mice. G7 is able to survive in host sera and phagocytes. In this study, we investigated the underlying mechanism of G7 serum resistance. We found that (i) the remaining complement activity was very low in G7-incubated flounder serum but high in G7-incubated mouse serum; (ii) cleaved C3 and C5 components were detected on flounder serum-incubated G7 but not on mouse serum-incubated G7; (iii) abundant uncleaved C5 was localized in G7-incubated mouse, but not flounder, serum; (iv) G7-incubated flounder, but not mouse, serum exhibited strong chemotactic activity; (v) pre-treatment with low-dose lysozyme abolished the serum resistance of G7. Hence, G7 activates flounder complement but is protected from complement-mediated destruction by its cell wall structure, while G7 prevents the activation of mouse complement. These results indicate that G7 employs different mechanisms to avoid the complement killing of different hosts. •G7 activates flounder complement leading to the cleavage of C3 and C5.•The cell wall of G7 confers protection against the killing by flounder complement.•G7 prevents the activation of mouse complement via unknown mechanism.•G7 employs different mechanisms to evade the complement killing of different hosts.