Pranay Lal - Invisible Empire: The Natural History of Viruses

Lets get this out of the way first:What, exactly, is a microbe? Quite simply: any life form that can only be seen under a powerful lens or microscope. And how many microbes exist in the world? If you were to say a trillion to the power of trillion, chances are you will still be well short of the actual number, which is likely to be inestimable, perhaps even unimaginable. Consider this: the ongoing COVID-19 pandemic (short for coronavirus disease 2019) started out as a tiny speck in the airway of a wild animal before it passed through hundreds of millions of human lungs, trailing havoc in its path. At the time of writing this, there have been nearly 122 million recorded cases of COVID-19 in the world. A British mathematician has, however, estimated that all of the worlds circulating SARS-CoV-2 (short for severe acute respiratory syndrome coronavirus 2, the causative agent of COVID-19) virus could easily fit inside the confines of a single can of cola!

From what we know, only an infinitesimally small fraction of microbes make us sick, even fewer have the power to kill us. Most simply pass through us, and a few use us as a suitable substrate to make more of their kind. They usually dont bother us in the least and some, in fact, many, actually do us good.

In every pinch of undisturbed soil, in every drop of water, there live a billion bacteria and ten times that number of viruses. Every lungful of breath we take contains about a thousand microbes. Most of them are unknown to us. Into this mysterious universe of microbes, come the scientists diving deep, like Captain Nemo, stooped over modern microscopes. They sit gazing at a wondrous world to explore the lives of predators and prey, producers and parasites. Some of the microbes are solitary, a few are in conjugal bliss or are colonisers; many are barely minutes old, the rest are mature, dying or already dead. Each speck of life you see under a microscope has a well-defined role, and in their plurality, they make up habitats no less complex than that of a multi-storeyed tropical forest. The crucial difference is that life in the microbial world plays out several times faster. Microbes come in tantalising forms and often in geometry-defying shapes. They can be translucent and iridescent, twitching or fleeting as one watches them; a plethora of awesome diversity in just a thimbleful of pond water or in soil taken from under leaf litter.

There is no singular world of microbes. Every ecosystem has its own set of curious microbial communitiesfrom the freezing ice of Antarctica to the hot sands of the Sahara, in the placid pond in your neighbourhood to deep-sea volcanic vents. They are everywhere. The surface of a pond teems with numerous photosynthetic organisms. Delve just a foot deeper and the character of organisms changes, while the benthic bottom of the pond and its sediments may have nothing in common with what is on top. A change of seasons or even the time of day can alter the proportions and number of microbes present. Microbial diversity shifts across the surface of the Earth as a consequence of the same three forces that Charles Darwin highlighted to explain the diversity of plants and animals environment, dispersal and diversification. Microbes mirror the same geographic patterns of diversity as those found in larger organisms, with the variety of microbes (or bacterial species richness) twice as large in the warmer tropics than it is at the frigid Poles.

Microbes come in bewildering shapes, are deeply complex, and in terms of sheer numbers are unmatched by any other life form. Try this for sizeit is estimated that there are 100 million times as many bacteria in the oceans (1.3 1029) as there are stars in the known universe. There are more microbes in natural water than in the soil around it, or in the air above. Even on dry land, their numbers are immense and surpass the imagination. The average number of microbes in a single teaspoon of soil (109) is as large as the human population of Africa. The human jowl alone, on average, has more than 6 billion microbes that can be made up of more than 600 separate species. A single gram of the stale-smelling yellow grimy film on our teeth, good old plaque, has approximately 1011 bacteria, which is about the same number as that of all the humans that have ever lived.

Under a microscope, a pinch of moist soil (1) from the edge of a pond reveals wondrouscreatures. A 2-millimetre worm-like nematode wriggles like a giant amidst the soil debris. About 4/5 of all animals on Earth are nematodesthere are 57 billion nematodes forevery human on earth. A single gram of soil can house up to several hundreds of these tinybacteria-feeding worms. If you dive deep using your lens, between grains of soil where thereare pockets of water you can see protozoa, like the translucent slipper-shaped