We All Contain Multitudes

I just finished reading another book that might go on my purchase list, I Contain Multitudes by Ed Yong. The author, a distinguished science-writer, does a magnificent job immersing the reader in the strange and wonderful world of microbes. This book is even better than Gut, an engaging exploration of the tiny and amazing creatures in our gut. Yong does cover the fascinating world of gut microbes, but his book is larger in scope. The vignettes alternate between sweeping vistas and carefully chosen tales of particular actors – Wolbachia makes its appearance in many places.

While microbes are fascinating in themselves, their interaction with larger creatures including mammals such as ourselves is even more interesting! I learned about the razor edge in which our co-evolutionary symbiosis with microbes could well turn into dysbiosis (a new word I learned!) as nature unfolds in ways that cannot be easily predicted. What makes it hard to predict is that we, by this I mean ‘we’ in multitude, form a complex ecosystem sitting in another larger and yet more complex ecosystem. Like maroshka dolls. And yes, there are bacteria within other bacteria. Yong discusses some interesting examples where tiny creatures that have occupied a niche within another organism over evolutionary time have interesting genomes – many of them stripped down to the bare essentials.

Insects are prominent examples in Yong’s book. That’s because some of the wildest and most bizarre relationships between microbes and larger organisms come from the world of insects. I learned that after a “beewolf digs her burrow, and before she adds an egg, she presses her antennae against the soil and squeezes a white paste out of them, like toothpaste from a tube. She then shakes her head from side to side to daub this secretion against the burrow’s ceiling. The paste is an exit sign: it tells the young beewolf where to start digging when it is ready to leave the burrow.” But what is more interesting is that the paste was full of antibiotic-producing bacteria. Without this, the young wasps all died from fungal infections. The tsetse fly, known for causing sleeping sickness, provides microbes to offspring still in the body of its parent. Yong describes it as “an insect that’s trying very hard to be a mammal. Rather than laying eggs, it gives birth to live young. And rather than hedging its bets with a horde of offspring, it devotes its energies to a single grub, which it raises inside a uterus and feeds with a milk-like fluid [full of microbes].”

Many other strange creatures are described, for example, the hydra that easily regenerates its lost limbs and can even survive being turned inside out. These tiny and seemingly simple creatures, come with their own microbiomes – protectors from infections of all kinds that would otherwise torment a creature that essentially consists of only a thin layer of epithelial cells. The aphid survives on tree sap. How does it get the other half of the required amino acids? Turns out that microbes help build what it is needed, in cooperation with its host. The weird giant tube worms found at scaldingly hot (well over 200 degrees Celcius) acidic hydrothermal vents on the ocean floor – you’d think no life would even survive there – thrive in droves even though they have no mouth or gut. Turns out there are loads of bacteria that help with chemosynthesis, drawing energy from sulfur-containing compounds.

One thing that struck me is the speed at which evolution can shape microbe populations. We large lumbering beasts change much more slowly; we might be adapting poorly to an environment that is changing so much more quickly than we can handle. If not for quick-adapting microbes, we might have much more trouble with food digestion, our immune-defense mechanism, and more. The fact that we all contain multitudes that co-evolve, for better or for worse, may be one of our most important discoveries and also one with the greatest potential for advancing human health. Yong provides a number of fascinating examples at the cutting edge of synthetic biology, detailing both their promise and the inherent difficulties of such approaches. “[The] microbiome [involves] large, changing networks of connected, interacting parts. To control a microbiome is to sculpt an entire world – which is as hard as it sounds… This is why attempts at world-shaping have so far led to a few magnificent successes, but also many puzzling setbacks.”

Reading this book momentarily made me consider switching fields and becoming a biologist. There was even a vignette on Oxalobacter, the bacterium that eats oxalate and therefore could potentially reduce the most common type of kidney stone, calcium oxalate. Then again, that’s also chemistry! (And I managed to incorporate calcium oxalate and calcium carbonate as a theme into my final General Chemistry problem set for the semester! And this was before reading Yong’s example.)