The Benefits of Being Small
There are many benefits to being small. Why, for example, are animals and plants made of so many tiny cells instead of being made of one big one?
Well, being made of lots of little components allows for greater diversification. It’s the difference between having a staff of several trillions versus trying to perform all the work of that crew on your own. Being large requires a lot of energy to perform many different tasks. The duties of the cells in your gut or kidney are very different from those carried out by cells in your brain or heart. And thank goodness for that – a regularly pulsating small intestine, or the formation of memory inside your liver doesn’t sound so fun. My liver would be full of many sad and regrettable memories. So, being small allows for the development of diversity. Also, consider the activity of one blob, 5”11’ of height and 160lbs of weight to its name (in my case). Controlling and concerting all the metabolic activities of one huge unit would require a huge amount of constant effort, and take a very long time. Every cell in our bodies is required to perform metabolic tasks of huge variety – both in levels of complexity and complicatedness. Metabolism, on top of copying and transcribing and translating DNA into proteins and all the other countless biochemical activities undertaken, is no mean feat. Being small also increases the available surface to take in critical substances and expel those which need to be expelled. In addition, there’s a huge turnover in our bodies of its smallest component parts – cells don’t live very long, but they are swiftly and efficiently replaced (sometimes, a little too swiftly, and a little too inefficiently, leading to the production of tumors). The life span of cells is highly dependent on the cell type and the nature of the work assigned to them – in the liver, your cells may be replaced every 300 days. Skin cells are recycled, potentially, every two weeks. Red blood cells are replaced, on average, every four months. White blood cells hang out for around a year. Brain cells, on the other hand, will last you your whole life and are not replaced when they die. So you’d best look after them. There are, comparatively speaking, very few cells in your body older than ten years.
Microbes, in comparison, are mostly unicellular, and are small in the traditional tangible sense of the word. Although, this being biology, there is always a fairly spectacular exception to the rule. Most fungi are multicellular, and a specific fungal being who lives in the Blue Mountains of Oregon is considered to be the largest living thing on Earth. This member of the Armillaria genus is over 2 miles across. But, there are unicellular fungi too: all yeasts, for example*. All the described efficiencies of being small are transcribed onto unicellular microbes, furthermore, they demonstrate an astonishing, unfathomable range of metabolic capacities. They can eat eat arsenic, live in hydrothermal vents, live in stomach acid. They exist at the very bottom of our oceans, where they survive, among other challenges, huge mechanical pressure by slowing their metabolism down to a rate of almost nothing. They proliferate in asphalt lakes of tar, radioactive waste, the Dead Sea, the Dry Valleys or Antarctica, in terrestrial caves 12 miles down. In addition, every living thing is colonized by microbes. In every environment they are found, microbes thrive. They thrive.
However, this remarkable survivability is usually mediated by their interactions with other microorganisms, and eventually larger beings. Microbes know when it’s in their best interest to diversify outside the constraint of their immediate being. Anabaena is a very charismatic genus of cyanobacteria that grows in long chains. These filaments are comprised mostly of vegetative cells, which perform photosynthesis and assorted metabolic tasks required by the cell to grow and reproduce. Interspersed throughout are a different kind of cell, heterocysts, which process otherwise biologically unavailable nitrogen, making it accessible to greater trophic spheres. Heterocysts are still Anabaena….only different. It is this compartmentalization of tasks which has allowed Anabaena and other genera alike to become so evolutionarily successful and adaptive.
Many microorganisms in the environment also form consortia that we call biofilms. Biofilms are complex and complicated heterogeneous structures, full of incommensurable individual unicellular and multicellular beings. They are microbial communities stacked on top of microbial communities. Being a card-carrying member of a biofilm affords physical protection, and community solutions to many varied tasks, metabolic and otherwise. Such consortia can be very old, or very young, they can be large or small. Some biofilms are made of one kind of bacterium (largely in laboratory, engineered or clinical settings). In these situations, left unchecked, biofilms can clog your sewer lines, kill animals, or bring down a plane. In association with larger organisms, bacteria can perform astonishingly beautiful and poetic feats. The Hawai’ian bobtail squid has such a relationship with the bacterium we call Aliivibrio fischeri. While the squid provides the bacterium with nutrition to survive, in return A. fischeri colonizes the squids light organ and produces bioluminescence. The light organ is very similar to an animal’s eye – it has a lens, reflective tissue and an analogous iris. When the light organ emits luminescence to the rest of the world, it’s very close to the quality of the light from the moon and the stars at night – so, for any opportunistic predator swimming underneath a squid, looking up at night, the squid is camouflaged. At dawn, the vast majority of the bacteria in the squid are ejected, only to repopulate during the day so that the squid has a full complement by nightfall. But how do the bacteria know when to start shining?
It’s a population threshold based mechanism, and it’s mediated by a type of bacterial communication called ‘quorum sensing’. Each bacterium releases molecules called an autoinducer that diffuse in and out of bacterial cells present in the squid’s light organ. The more bacteria present, the more autoinducers released. Once the concentration of autoinducers in the light organ reaches a certain level, every single V. fischeri cell alters their gene expression, and begins to emit light. This microbe does not live in the squid’s cells – instead it inhabits a nest that has been specially crafted for the very purpose of allowing it free ingress and egress in order to support the life of the squid, and for it to be supported in turn. This relationship was brokered over evolutionary timescales, and it is wholly susceptible to bacterial community effort and communication. The Hawai’ian bobtail squid and A. fischeri are partners for life, mutually, and dynamically.
Being small and feeling small are not the same thing: they’re two sides, good and bad, of the same coin. There’s a choice to be made between feeling insignificant, and recognizing that every living thing is part of a massive network of biology, physiology, and thought. Don’t ever forget that we, as human people, are a sum far greater than our pasts and our attempts to make amends for past mistakes. We all have a rich and deserved role in the present, and the future for hundreds of years to come, as one small component in something overwhelmingly huge.
*Yup, yeasts are fungi. See Saccharomyces cerevisae, the species responsible for many of the aforementioned bad liver memories due to its role in brewing. It’s also used in baking (‘baker’s yeast’) and a range of other commercial applications, was a crew member of the Living Interplanetary Flight Experiment, is a helpful model in the study of aging, and its name translates to ‘sugar fungus’.
Below is a portrait of your humble author, that a friend of mine painted with bioluminescent bacteria. This was a rare and priceless honor for me. L-R: original photo, painting under normal light, me glowing, me REALLY glowing