Illustration of Enterobacteriaceae, a family of bacteria that includes the gut-dwelling species ... [+]
Scientists suggest that light could be used to manipulate the metabolism of gut bacteria to prolong our lifespans.
The approach would involve a technique called 'optogenetics', where cells are engineered to have genes that respond to light, meaning you can then control an organism's genetic activity — even its behavior — through light.
Optogenetics allows you to switch certain genes on or off at will, so some scientists believe it could be used to activate metabolic processes within gut bacteria that would benefit the health of their human hosts, which might help extend your lifespan.
That potential application has now been demonstrated in a proof-of-concept study led by synthetic biologist Jeffrey Tabor of Rice University and ageing researcher Meng Wang at Baylor College of Medicine in Houston, Texas. In a paper titled 'Optogenetic control of gut bacterial metabolism to promote longevity', the pair found that they could use different colors of light to turn-on specific genes in the bacterium E. coli inside the intestine of a nematode worm, Caenorhabditis elegans.
The genes are involved in producing a metabolite called 'colanic acid'. In an earlier study, Wang showed that worms would live up to 45% longer if their gut contained bacteria that were genetically engineered to make extra colanic acid.
Colanic acid promotes longevity by helping mitochondria, the energy-generating 'power stations' inside cells. Mitochondria become less efficient with age, but colanic acid seems to enable the generators to function more efficiently again.
Light-responsive bacteria can be seen inside a worm's gut thanks to red and green fluorescent ... [+]
In the latest research, Tabor's team created E. coli that would only produce colanic acid when exposed to green light. The success of using optogenetics was highlighted by linking colanic-acid genes to those for two fluorescent proteins. Under a microscope, the bacteria would glow from green fluorescent protein (GFP) or a red fluorescent protein (Cherry) when treated with light, which showed that the bacterial cells were indeed producing colanic acid.
When treated with green light, the gut bacteria produced more colanic acid and their worm hosts lived slightly longer (an increase of up to 3 days, around 30%). The extent of such life extension depended on the strength of the dose. As Wang says, "The stronger the light, the longer the lifespan."
The community of microorganisms that colonize a human body — the 'microbiome' — affects health, and studies have shown that bacteria in our gut microbiomes influence our susceptibility to a wide range of conditions — everything from obesity and diabetes to cancer and cardiovascular disease.
As your gut bacteria are effectively part of your inner metabolism, controlling them through optogenetics could reduce your risk of certain conditions. While it can be hard to target a particular part of the body — such as your gut — using approaches such as drugs, a beam of light could switch-on life-enhancing genes in modified microbes at a specific time and place within your digestive system.
"The goal, the thing you really want, is gut bacteria you can eat that will improve health or treat disease," says Tabor. "Light is really the only signal that has enough precision to turn on bacterial genes in the small versus the large intestine, for example, or during the day but not at night."
