Can microbes fight our battles for us?

So you’ve heard about probiotics; the ‘good’ bacteria in those yoghurt adverts that keep your gut healthy and your poo in great shape.

But have you heard that lobsters have bacteria that protect them against fungal infection?; and bullfrogs have mysterious microbes on their skin that defend against fatal disease? Aphids even have bacteria that protect them from parasitoid wasps laying eggs in them and chestnut trees harbour viruses that protect them from pathogenic fungi. In humans it’s even been found that breast milk contains an important community of microbes that protect against the growth of harmful bacterial species.

Microbes that protect their host organisms from infectious disease are termed defensive microbes. And they’re actually pretty common.

In the era of antibiotic resistance, where pathogens are evolving ever-increasing levels of resistance to antibiotics, people have been wondering whether we can use some of these nifty bugs to control disease. This has major implications for human health, agriculture and the conservation of endangered species threatened by disease.

One cool example is the introduction of a bacterium called Wolbachia into mosquitoes that limit the growth of various mosquito-borne parasites including Dengue Virus, Malaria, Yellow Fever, Chikungunya, West Nile Virus, filarial nematodes and even Zika virus. The bacterium is naturally found in 40-60% of all insects and was found to protect fruit flies from viral infection. Within mosquitoes, however, Wolbachia harness a great potential to abolish the transmission of mosquito-borne disease.

This is pretty awesome.

But have we thought what might happen if we fill the world with defensive microbes?

Not really.

This week I published a paper in PLOS Pathogens entitled "Harnessing the Power of Defensive Microbes: Evolutionary Implications in Nature and Disease Control" (http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1005465) discussing three questions on the evolutionary implications of defensive microbes:

1) How persistant will protection by defensive microbes be in the face of parasite resistance evolution?

2) Will defensive microbes select for hosts that don't defend themselves?

3) Will defensive microbes affect the evolution of how much a pathogen harms their host (termed virulence)?

Defensive microbes can use various mechanisms to protect their hosts from pathogens. In my paper I propose that it is these mechanisms that determine the answers to questions 1-3 and how. As we uncover more about defensive microbes in nature and how they interact with hosts and their pathogens we will likely gain invaluable knowledge of what traits make certain defensive microbes good or bad choices as disease control agents.

Watch this space.

"Harnessing the Power of Defensive Microbes: Evolutionary Implications in Nature and Disease Control" : http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1005465

Image: mosquitoes responsible for the transmission of Dengue Virus, Aedes aegypti

Image credits: Steve Morton. Scientific Imaging Service. Monash University, Australia