Sushi and Stramenopiles3 April 2019
Three and a half years ago, in a first year Genetics and the Evolution of Life lecture, I had an academic epiphany. The lecture itself was not one that you would expect to convert an aspiring speech pathologist into a marine biologist: the lecturer had inherited this section of the course from an academic who retired the previous year and had about as much idea of what was going on as we did. Blocks of lurid yellow text covered blue backgrounds, and the same slide of ‘Snowball Earth’ kept inexplicably popping up with zero explanation. But something shone through the less than stellar delivery that ignited a spark of passion in me.
The lecture was on protists, a broad group of life ranging from tiny marine microbes to massive brown kelps. If you take all complicated life (which is not prokaryotic like bacteria), everything that is not a plant, animal or fungus is a protist. It’s a grab bag group of left-over lineages that are not more genetically related to each other than everything else, they’re just less appreciated. While there are some macroscopic protists, seaweeds for example, a vast majority of them can only be seen under a microscope and thus go unobserved and unappreciated by people every day.
So, what is so fascinating about these weird organisms? Firstly, they are everywhere: snow, soil, sand, the guts of termites, the ocean and freshwater. When corals bleach, they’re kicking out the dinoflagellate protists that live inside of them and give them their colour. Lichens, the crusts you sometimes see on rocks, trees and railway platforms, are a fungus that has either a protist or bacterium living alongside it. Even dead protists leave their mark, with the calcium carbonate skeletons of single cells called coccolithophores building up over millions of years into chalk deposits like the White Cliffs of Dover.
Some protists are of big concern to human health: Malaria, the terrible parasite whose death toll reached 435,000 in 2017 according to the World Health Organisation, is a protist. Along with Toxoplasma gondii, the brain parasite famous for being transferred from cats to humans, it is in the group Apicomplexa that is somewhat closely related to the dinoflagellates you find inside corals. Giardia is a bug-eyed looking protist that causes an unpleasant diarrhoeal disease which, while on exchange in Canada, I heard referred to as ‘beaver fever’.
But it’s not all bad. Seaweed such as nori (in the genus Pyropia, which you’ll find wrapped around your sushi rolls), are an important part of many diets around the world and are rich in fibre and protein as well as many nutrients including iodine, calcium and magnesium. Protists also produce a range of products that we as humans use every day. Carrageenan and Agar (vegan gelatine) are produced by red seaweeds and used as gelling, thickening and stabilising agents in food and other products, like toothpaste. Agarose, a purer form of Agar, is used in biochemistry and microbiology.
However, the real reason I fell in love with protists is simply because of how beautiful they are. Look at a drop of pond water under the microscope and you will find a forest teeming with life, hundreds of tiny cells surviving and interacting. Ciliates rhythmically beat their hair (cilia) as they dart between long green filaments of cyanobacteria or green algae, seeking out bacteria or algal prey. Boat-shaped pennate diatoms glide smoothly along the surface, encased in cell walls made of glass, while golden brown dinoflagellates whirl in a corkscrew spiral so quickly they are nearly a blur. Amoebae spread out thin like glistening pancakes and countless tiny colourless flagellates zip in and out of view. It is like the entire range of colour, symmetry and shapes available to mother nature (or rather, the force of evolution), the origins of all the complexity that makes up humans and the rest of our complex world, can be observed in only a millilitre or so of murky water.
My small glimpse into that world changed my life. The past three and a half years have seen me change my major, hassle a series of unsuspecting academics for mentorship and advice, and go all the way to the east coast of Canada for a single course on microbial protists. I have unleashed the full brunt of my enthusiasm on innocent students taking Marine Botany. I have learnt to do biology on computers and have analysed the proteins from a cell in a whole new class of life. When honours work gets too much and the imposter syndrome kicks in, I head upstairs and look at my cultures under the microscope. Watching a sea of little green ovals (Pedinophytes) wriggle in lazy circles reminds me of the sense of wonder I first felt in that lecture about these strange beautiful organisms that can teach us so much about life on earth.