Deep-Sea microbial-host interactions might hold keys to deadly pandemic diseases (like COVID-19)

by Anshika Singh: The whole world is going through a tough time and everyone is interested in finding answers to only one question: when will this pandemic end and what can be done in the future to keep this from happening again?

Different researchers have come up with various concepts such as herd immunity, protection of wild habitats, bans on wildlife trade and consumption to prevent spill over. In a nutshell, everyone is now understanding the concept of ONE HEALTH and how important it is to maintain ecosystem balance.  The SARS-CoV2 (COVID-19) pandemic has also taught us how important it is to explore models that can help us to understand immune response to an unknown pathogen.

In this line, there has been a very interesting study conducted by a group of scientists in the central Pacific Ocean in the Phoenix Islands in Kiribati, 1650 miles (2655 kilometers) from Hawaii [1]. They found that marine pathogens (certain marine bacteria) are completely unidentified by human immune cells, despite the presence of the typical bacterial cell wall component lipopolysaccharide (LPS) which is, otherwise, detectable by our immune system. Some pathogens such as the rodent bacterium causing plague, Yersinia pestis, also escape the host immune system by modifying their LPS [1]. It is very interesting to note that these deep-sea pathogens that have never been in close contact with humans can go undetected by our immune system, thus escaping potential human immune response. These deep-sea bacteria were found to be gram-negative and from the genus Mortitella [1]. A closer look at their cell walls helped the scientists to discover the reasons for their invisibility to the human immune system [1].  Deep-sea bacteria had LPS with longer chains that helped them to go undetected from mammalian LPS receptors, thus escaping the immune responses and causing “immuno-silencing”. This finding has shaken the fundamental notion in immunology that suggests that the human immune system has evolved to detect and respond to any pathogen [1]. It suggests that there can be some pathogens from extreme environments such as deep-sea, hydrothermal vents and polar ices that can escape our immune responses and could infect us if we come in contact with them.

Although the findings were alarming, these bacteria were found harmless to humans. However, it does intrigue scientists to carry out more deep-sea research to understand how the local host defense system acts against these pathogens. The interaction between deadly microbes and host defense mechanisms is a decisive factor for the survival of many deep-sea animals (especially bottom dwellers). They rely on cell‐mediated and humoral reactions to overcome the pathogens that naturally occur in the marine environment. Several studies have suggested that deep-sea creatures such as anglerfishes, sponges, mussels, shrimps, and oysters can hold answers to many of our diseases as these animals have evolved special immune response to cope with the hostile environmental challenges. For instance, anglerfishes showed unique behaviour of sexual parasitism where they allow fusion of male tissues for reproductive success [3]. Males are often found to have compromised innate immunity to allow successful fusion and reproduction. Understanding how the anglerfishes can maintain a healthy life despite non-existing innate immunity can allow for the exploration of immunosuppression in humans and designing better treatments for organ transplant recipients in the future.  Similarly, sponges from different but closely related species are also able to fuse, thus serving as a good model system to understand innate immunity [4].  Mussels, shrimps and oysters show unique immune responses against deep sea pathogens, providing us useful insights into their unique pattern recognition receptors (PRRs) [5-6].

Many gene products and signalling pathways share striking similarities between mammals and marine invertebrate innate immune reactions, suggesting conserved mechanisms during the course of evolution [7]. They can serve as a useful model system to understand how to boost up the immune system against new pathogens.

References:

1. Gauthier, A. E., Chandler, C. E., Poli, V., Gardner, F. M., Tekiau, A., Smith, R., … & Kagan, J. C. (2021). Deep-sea microbes as tools to refine the rules of innate immune pattern recognition. Science Immunology, 6(57).
2. Ba Abduallah, M. M., & Hemida, M. G. (2021). Comparative analysis of the genome structure and organization of the Middle East respiratory syndrome coronavirus (MERS‐CoV) 2012 to 2019 revealing evidence for virus strain barcoding, zoonotic transmission, and selection pressure. Reviews in Medical Virology, 31(1), 1-12.
3. Swann, Jeremy B., Stephen J. Holland, Malte Petersen, Theodore W. Pietsch, and Thomas Boehm. “The immunogenetics of sexual parasitism.” Science 369, no. 6511 (2020): 1608-1615.
4. Müller, W. E., Koziol, C., Müller, I. M., & Wiens, M. (1999). Towards an understanding of the molecular basis of immune responses in sponges: the marine demosponge Geodia cydonium as a model. Microscopy research and technique, 44(4), 219-236.
5. Bettencourt, Raul, Inês Barros, Eva Martins, Inês Martins, Teresa Cerqueira, Ana Colaço, Valentina Costa et al. “An insightful model to study innate immunity and stress response in deep-sea vent animals: Profiling the mussel Bathymodiolus azoricus.” Organismal and Molecular Malacology 8 (2017): 161-187.
6. Bachère, E., Gueguen, Y., Gonzalez, M., De Lorgeril, J., Garnier, J., & Romestand, B. (2004). Insights into the anti‐microbial defense of marine invertebrates: the penaeid shrimps and the oyster Crassostrea gigas. Immunological reviews, 198(1), 149-168.
7. Hoffmann, Jules A., and Jean-Marc Reichhart. “Drosophila innate immunity: an evolutionary perspective.” Nature immunology 3, no. 2 (2002): 121-126.