Interactions between Lipopolysaccharide and Peptide Bacteriocin BacSp222 Influence Their Biological Activities

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Pro-inflammatory factors from bacteria, such as lipopolysaccharide (LPS) and antimicrobial peptides, play crucial roles in host-pathogen interactions.
• Understanding the interplay between different bacterial molecules is essential for developing novel therapeutic strategies.

Purpose of the Study:

• To investigate the interaction between lipopolysaccharide (LPS) from Gram-negative bacteria and the bacteriocin peptide BacSp222 from *Staphylococcus pseudintermedius*.
• To determine how this interaction affects their respective biological activities in vitro and in vivo.

Main Methods:

• In vitro assays measuring tumor necrosis factor (TNF) and nitric oxide (NO) production by monocyte-macrophage cells.
• In vivo studies using *Galleria mellonella* larvae to assess immune response (hemolymph phenoloxidase activity).
• Gel filtration and isothermal microcalorimetry to analyze molecular complex formation and interactions.

Main Results:

• Co-treatment with LPS and BacSp222 significantly reduced TNF and NO production compared to LPS alone, suggesting BacSp222 interferes with LPS-induced TLR4 stimulation.
• In *Galleria mellonella* larvae, co-injection of LPS and BacSp222 resulted in lower hemolymph phenoloxidase activity than individual treatments.
• Electrostatic interactions between LPS micelles and BacSp222 led to complex formation, reduced LPS aggregate size, and altered biological activities of both molecules.

Conclusions:

• LPS and BacSp222 interact electrostatically to form a complex, thereby modulating their pro-inflammatory and immune-modulating functions.
• This molecular interaction offers a potential mechanism for mitigating excessive inflammatory responses triggered by bacterial components.
• The findings highlight the complex interplay between different bacterial molecules and their impact on host immunity.