The zebrafish and its gut symbiont, Aeromonas veronii, provide a powerful model for understanding host-microbe mutualism. Specifically, the bacterium produces a novel immunomodulatory protein, AimA, crucial for peaceful coexistence. This discovery highlights the importance of incorporating host-microbe interactions into comparative physiology research.
Aeromonas veronii, a bacterium residing in the zebrafish gut, produces a unique molecule, AimA (Aeromonas immune modulator A), to suppress the host’s immune response, fostering a mutually beneficial relationship. This intricate interaction exemplifies the complex interplay between host and microbe, underscoring the need for its inclusion in the comparative physiologist’s toolkit.
AimA: A Key to Understanding Host-Microbe Mutualism
Symbiotic relationships, particularly those in the gut, are essential for host health and well-being. While research has often focused on host benefits, understanding microbial contributions is crucial. The study by Rolig et al. (2018) sheds light on this aspect using the zebrafish- Aeromonas veronii model.
A. veronii is a persistent symbiont throughout the zebrafish lifecycle, playing vital roles in immunity, gut development, and pancreatic function. Rolig et al. demonstrated that a specific strain, Hm21, produces AimA, a molecule that dampens the inflammatory response of neutrophils, the first responders of the immune system.
Unraveling the Mechanism of Immune Modulation
AimA’s amino acid sequence is novel, but its 3D structure resembles Lipocalin-2, a protein secreted by human neutrophils. This structural similarity suggests a competitive mechanism for receptor binding on immune cells, supported by experiments where mouse Lipocalin-2 interfered with AimA’s protective effects.
Further investigation revealed that AimA is crucial for A. veronii colonization and host health. Bacteria lacking AimA and its paralog, AimB, failed to colonize the zebrafish gut, leading to increased neutrophil numbers and inflammation. However, adding purified AimA restored colonization and normalized neutrophil levels.
Broadening the Scope of Comparative Physiology
This study underscores that mutualistic factors, like AimA and the polysaccharide produced by Bacteroides fragilis, are critical for establishing and maintaining symbiotic relationships. AimA’s anti-inflammatory properties and unique structure also hold potential therapeutic value.
The zebrafish-Aeromonas model provides a valuable tool for dissecting the molecular mechanisms underlying host-microbe interactions. By incorporating these interactions into their toolbox, comparative physiologists can gain a more comprehensive understanding of organismal function and adaptation. This research emphasizes the importance of basic research using simple animal models to unravel complex biological phenomena. Future studies exploring the broader implications of AimA and similar molecules could revolutionize our understanding of host-microbe symbiosis and its impact on health and disease.
Conclusion: A Call for a Holistic Approach
The discovery of AimA highlights the intricate interplay between host and microbe, emphasizing the need for a more holistic approach in comparative physiology. By integrating host-microbe interactions into their research, scientists can gain a deeper understanding of organismal function, adaptation, and the evolution of symbiotic relationships. The zebrafish- Aeromonas model provides a powerful platform for future studies exploring the complex dynamics of host-microbe mutualism.
