The secret of long life? Dine on the kids’ doo-doo

If you’re a turquoise killifish, that is.

In the last couple of weeks, researchers in Germany have released the findings of a remarkable study in which they were able to dramatically increase the longevity of middle-aged fish by replacing the contents of their gut microbiome with microbes taken from younger fish of the same species.

We’re reporting on this with the minor caveat that the paper has only been published in preprint form, so it hasn’t yet been peer-reviewed. However, a recent piece about the research in Nature quotes a developmental biologist and geneticist from the Buck Institute for Research on Aging, in Novato, California (not involved in the study) as saying: “The paper is quite stunning. It’s very well done.”

So, what can we tell you about it?

Well, the researchers involved were based at the Max Planck Institute for Biology of Ageing, in Germany.

And the particular species of fish they studied was the turquoise killifish, originally a native of Zimbabwe and Mozambique, but often bred specifically for studies in aging.

The turquoise killifish, or Nothobranchius furzeri to give it its full scientific name, is the shortest-lived vertebrate that can be bred in captivity.

You’d imagine that the last thing you’d need as a creature with such a brief life is a name that takes you all day to say, but we suspect Nothobranchius furzeri itself didn’t really get much say in what it was called.

Exactly how brief is this eight-syllabled creature’s life?

Well, when bred in captivity, a killifish generally lives to be between just four and eight months of age.

It becomes sexually mature within three to four weeks, and its fertility peaks between eight and ten weeks.

At nine-and-a-half weeks, a poor old killifish is considered veritably middle-aged.

Now if, like us, you’re agog to know why such a short-lived creature could have evolved in the first place, it’s because their natural habitat is in what are known as ephemeral ponds (sometimes also called “vernal” pools, where vernal means Spring) that form during rainy seasons.

But how the heck do fish manage to show up in temporary ponds in the first place?

Amazingly, the eggs of most types of killifish (and there are almost 1,300 different species) can survive periods of partial dehydration, so they are able to lie dormant in almost dried-out pond bottoms from one year to the next.

In fact, apparently, it’s even possible to send killifish eggs through the mail without water, just like seeds.

Clearly, when you’re studying longevity in vertebrates, it helps enormously to focus on creatures that normally live only briefly because, as a researcher, you get to see your results before you, yourself, die.

The Greenland shark, for example, would be a less-than-ideal subject, as it appears to live for at least 200 years, which would make for very long-winded experiments, not to mention rather large fish tanks.

The researchers in Germany found a clever way to “transplant” the microbiome from six-week-old killifish into middle-aged (nine-and-a-half week old) killifish, having first established that the gut microbiome of killifish become less diverse as the fish age, as is also known to be the case in rats and humans.

The scientists began by treating the middle-aged fish with an overnight cocktail of antibiotics, which essentially sterilized their guts.

The fish were then placed in a tank of sterile water into which the gut contents of young killifish had been introduced.

Now, middle-aged killifish aren’t exactly big on eating kid poop (who is, frankly?), but since there was no other chow around, they were inclined to probe and bite at it, in order to learn whether it was in fact their lunch, disguised as something else. In the process, they ended up ingesting microbes.

And that’s where things began to get very interesting.

The researchers recorded the lifespans of the fish who’d received the transplants, alongside those of control groups.

One of these control groups went through the same antibiotic sterilizing process, but were then fed middle-aged fish feces.

The median lifespan of those getting young poop was a massive 41% longer than those who received middle-aged poop.

And it was 37% longer than fish who’d received the antibiotic treatment alone. (The researchers discovered that antibiotics on their own did have a slight positive effect on longevity.)

In fact, at 16 weeks old, the gut microbiomes of the killifish who’d received transplants from young fish still resembled those of these younger fish.

And, pretty stunningly, these 16 week old fish — who were old aged in killifish terms — were apparently darting around their tank more frequently than other elderly fish, exhibiting energy levels and aquatic acrobatics more like six-week old fish.

A bit spookily, past research by other scientists showed that piping young rat blood into an older rodent can increase the senior’s longevity, but this is the first study to suggest that transplanting a young microbiome into an older recipient can extend life.

Naturally, the German researchers say it’s way too soon to consider the possible implications of this study in terms of human life extension, but it has prompted a Canadian scientist to wonder if an individual’s microbiome, sampled and “banked” early in life, might extend the lifespan when subsequently reintroduced.

The mind boggles.

The Max Planck Institute scientists say it’s not really clear how microbes influence lifespan, though they do suggest one possibility could be that immune systems wear out with age, allowing harmful microbes to outcompete more beneficial bacteria.

If this is the case, a microbiome transplant might effectively “reset” a middle-aged fish’s microbiome.

Not unnaturally, the researchers are keen to move on from killifish to investigate other species.

So will they now be transporting poop from 12-year-old humans into 40-year-olds?

Not quite.

Their next target?

The fruit fly.


More reading

Killifish

Regulation of Life Span by the Gut Microbiota in The Short-Lived African Turquoise Killifish

The Poop of Young Fish Can Help Older Ones Live Longer

Vernal pool

‘Young poo’ makes aged fish live longer

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