The gut of just about any organism is surely an unpleasant place, often teeming with a battery of hostile enzymes.
Yet such places in animals often harbor multiple species of bacteria. But the exact physiological processes that allow some of these bacteria to thrive, while others perish, are not fully understood.
A group of researchers at the Yale School of Public Health is moving closer to explaining this dichotomy. They used the tsetse fly, which has only a few vertically transmitted symbiotic bacteria, to understand processes that allow some bacteria to live in harmony with their host. The Yale team discovered a mechanism that is at least partially responsible for the successful relationship between the tsetse fly and its symbiotic bacterium, Sodalis glossinidius. Sodalis, which is related to some important human microbes such as E. coli, Salmonella and Yersinia, likely benefits the fly by increasing its longevity and possibly modulating immunity.
The group investigated tsetse’s response to superinfection with its native Sodalis versus closely–related E. coli K12. While Sodalis was able to proliferate in tsetse, E. coli was surprisingly pathogenic. The researchers discovered that outer membrane protein A (OmpA) plays a key role in enabling the tsetse–Sodalis symbiosis. This protein comprises a major component of the eubacterial outer membrane. Sodalis’ OmpA was found to contain polymorphisms in its exposed loop domains when compared to homologues from closely–related pathogenic microbes. These loops encode virulent domains in the pathogenic bacteria. These observations were further substantiated when tsetse were found to be resistant to an E. coli OmpA mutant strain. This reaction appears to result from tsetse’s differential immune response to the different OmpA molecules.
Researcher Brian L.Weiss said that the group also discovered that other insect symbionts have polymorphisms in their OmpA molecules that are similar to those found in Sodalis. The group intends to follow up on this work by performing further experiments that aim to clarify how different OmpA molecules interact with the host immune system.
A better understanding of the nature of symbiotic relationships—which abound in nature and are crucial to the survival of most species—could eventually have implications for people suffering from degenerative bowel diseases, such as Crohn’s, said Weiss. The research group was headed by Serap Aksoy, professor and head of the Division of Epidemiology of Microbial Diseases.
Details of the research were published in the Early Edition issue of the journal PNAS.