Posted by Kasra
Given the extremely large amount of bacteria in our gastrointestinal track, it is not surprising to think that the gut would be also swarming with pathogens of bacteria, that is bacteriophages as well. In their recent work published in PNAS, Barr et al. take a look at what impact these particles could have on the population of bacteria in mucosal surfaces and what could it mean for us. Their work actually turns out very interesting results.
Mucosal surfaces are the body’s points of contact with the outside. Being highly populated with bacteria, they can be suitable points of infection as well. That is why they are heavily guarded with various immune barriers and mechanisms, both innate and adaptive. Barr et al. point to a possible mechanism of protection against infection which not innate nor adaptive. They start by comparing the amounts of bacteria and bacteriophages in different mucosal and non-mucosal surfaces in various mucus producing animals. They interestingly observe that the bacteriophage to bacteria ratio in mucosal sites is way larger than those in adjacent non-mucosal sites (from average about 40fold to average about 3fold). They verify this in both invertebrates and vertebrates and thus suggest that this could be a phenomenon in all mucus-producing metazoans.
Next, they point to a previous recent study by Minot et al. who had found immunoglobulin (Ig)-like domains in the total analyzed genome of human gut viruses (or so called human gut virome). These domains that usually act as in recognition and binding (as an antibody would do); they show that the bacteriophages actually bind to mucus through these proteins. Barr et al. also show that presence of bacteriophages on a mucosal surface significantly reduces Escherichia coli invasion in vitro.
This is an incredible system where the benefit of the bacteriophages and their hosts actually match. It is not clear at this point whether the animal body would have to do something other than producing mucus to keep the bacteriophages where they are or that it is just enjoying this protection more or less free of charge.
Barr JJ, Auro R, Furlan M, Whiteson KL, Erb ML, Pogliano J, Stotland A, Wolkowicz R, Cutting AS, Doran KS, Salamon P, Youle M, & Rohwer F (2013). Bacteriophage adhering to mucus provide a non-host-derived immunity. Proceedings of the National Academy of Sciences of the United States of America PMID: 23690590
Minot S, Grunberg S, Wu GD, Lewis JD, & Bushman FD (2012). Hypervariable loci in the human gut virome. Proceedings of the National Academy of Sciences of the United States of America, 109 (10), 3962-6 PMID: 22355105