Using Probiotics to Prevent Disease is Common in the Animal World
Posted by Richard Conniff on January 14, 2015
I light up whenever I see a story about hoopoes, colorful Old World birds, mainly for the silly reason that they have the coolest scientific name in the animal kingdom. I think it may just be impossible to say Upupa epops without smiling. I’m pretty sure these birds must be fans of 1950s jazz.
But let’s talk about the story, which is in equal parts intriguing and kind of annoying. Scientists have discovered that hoopoe moms laying their eggs automatically apply a bacterial film that protects their offspring from various pathogens. This is cool stuff: Birds using probiotics.
The press release says that this sort of behavior has never been detected before in any bird species. It thus gives the annoying impression that this is a totally new thing in science, which is of course not so. For at least the past half dozen years, for instance, scientists have been studying how certain salamanders and frogs apply a bacterial coating that protects their eggs from the deadly chitrid fungus and other pathogens, as I wrote here in 2013.
Indeed, all the writer of the press release needed to do was read the first paragraph of the study to learn that the science of probiotics in multiple species “is one of the most exciting discoveries in ecological immunology”:
Animals using chemicals from metabolism of symbiotic bacteria against pathogenic micro-organisms and parasites is one of the most exciting discoveries in ecological immunology. Bacteria produce an extraordinary diversity of antimicrobial compounds to inhibit other micro-organisms (Ji, Beavis & Novick 1997; Riley & Wertz 2002) and, when they are in symbiotic associations with animals, such chemicals may function for hosts as defences against pathogenic micro-organisms and parasites. For instance, chemicals produced by symbiotic bacteria are known to protect ants’ gardens, wood galleries of beetles and embryos of shrimp, lobsters, squid, wasps and some salamanders from pathogenic bacteria and/or competitor fungi (Gil-Turnes, Hay & Fenical 1989; Barbieri et al. 1997, 2001; Currie et al. 1999; Kaltenpoth et al. 2005; Cardoza, Klepzig & Raffa 2006; Banning et al. 2008; Scott et al. 2008), or aphid hosts from their parasitoids (Oliver et al. 2003), which illustrate the great variety of animals that use antibiotic-producing bacteria as defence against pathogenic infection.
What’s really exciting, and could have made a far better press release, is the idea that the animal world has its own complete science of probiotic medicine, which we are only beginning to figure it out. Anyway, here’s the annoying press release.
Researchers from the University of Granada and the Higher Council of Scientific Research (CSIC) have found that hoophoes cover their eggs with a secretion produced by themselves, loaded with mutualistic bacteria, which is then retained by a specialized structure in the eggshell and which increases successful hatching. So far this sort of behaviour has only been detected in this species of birds, and it is a mechanism to protect their eggs from infections by pathogens. Through an experiment published in the Journal of Animal Ecology, scientists from several research groups precluded several female hoophoes from impregnating their eggs with this substance, which they produce themselves inside the so-called uropygial gland. The research groups involved in this project were the following: Animal Behaviour and Ecology, Microorganism-Produced Antagonistic Substances, both from the UGR, and Evolutive Ecology and the Behaviour and Conservation groups from the Dry Areas Experimental Station (Almería, CSIC)
By doing so they confirmed that the amount of pathogen bacteria that could be found inside the eggs which failed to hatch was higher in those nests in which they had experimentally precluded the females from using their secretion than in those where they were allowed to use this substance. They concluded that this secretion provides a barrier for the entry of pathogens towards the interior of the egg.
Presence of enterococci
On the other hand, not just the secretion as a whole, but particularly the bacteria that did produce bacteriocins (small antimicrobial proteins) in that secretion, the enterococci, are beneficial for the developing embryos, since successful hatches were directly related to the amount of these enterococci in the egg shells and in the secretions of the females. The more enterococci they had, the higher the rate in their successful hatching.
As UGR zoology professor, Manuel Martín-Vivaldi, one of the authors of this research underlines, during the last few years the field of evolutive ecology has acknowledged “the important role played by bacteria, not just as infectious agents capable of producing diseases, but also as allies of animals and other living creatures in their struggle against disease, due to their extraordinary capacity to synthesise compounds with antimicrobial properties”
In the case of the hoophoe’s uropygical gland, scientists have confirmed that its components are very different from those of other birds. This is to a large extent due to the action of the bacteria present in this particular gland.
This research has also revealed that hoophoes have developed an exceptional property in their eggs — which has not so far been found in any other species of bird. This consists in the presence in the surface of many small depressions that do not completely penetrate the shell, and whose function appears to be the retention of this bacteria-carrying secretion that covers the egg.
Bacteria in the eggshell
“With this experiment, we have been able to establish that if the females can use their secretion, towards the end of the incubation period, those tiny craters are full of a substance saturated with bacteria. If we preclude the use of this secretion, these tiny craters appear empty towards the end of the hatching process,” said professors Martín-Vivaldi.
These results prove that in this particular species of bird, “its reproductive strategy has evolved hand in hand with the use of bacteria which may be beneficial for the production of antimicrobial substances, which they cultivate in their gland and then apply upon eggs which are particularly endowed to retain them”
These scientists are currently working to determine the specific composition of the bacterial community within the gland, how these symbionts are acquired, and the types of antimicrobial compounds which synthesize these bacteria, capable of protecting the embryos which are undergoing development.
Further research along these lines will facilitate a better understanding of the way in which mutualistic interactions function between animals and beneficial bacteria, and also to detect new antimicrobial substances with a potential to be used in medicine of for food preservation.
This study is the result of the following two projects: “Nests, parasites and bacteria: a multidisciplinary approach to the study of adaptation for breeding in high parasitism risk environments,” funded by the Ministry of Science and Innovation, and “Biodiversity and acquisition mechanisms in the bacterial community within the uropygial gland of hoophoes (Upupa epops), funded by the Department of Innovation, Science and Business of the Junta de Andalucía (within the Programme of Incentives for Excellence in Research)
- Manuel Martín-Vivaldi, Juan J. Soler, Juan M. Peralta-Sánchez, Laura Arco, Antonio M. Martín-Platero, Manuel Martínez-Bueno, Magdalena Ruiz-Rodríguez, Eva Valdivia. Special structures of hoopoe eggshells enhance the adhesion of symbiont-carrying uropygial secretion that increase hatching success. Journal of Animal Ecology, 2014; 83 (6): 1289 DOI: 10.1111/1365-2656.12243