What’s It All About, Algae?

These sun-powered green dynamos are so much more than pond scum.

Mature and daughter colonies of volvox (Chlorophyta, or green algae) found in freshwater. Individual alga have an eye spot, which helps direct the colony toward light, and two strands of cytoplasm, which bind the individual alga together, making the colony almost a multi-celled organism.


Excerpted from SLIME: How Algae Created Us, Plague Us, and Just Might Save Us by Ruth Kassinger. Copyright © 2019 by Ruth Kassinger. Used by permission of Houghton Mifflin  Harcourt. All rights reserved.

Algae are Earth’s authentic alchemists. Using sunlight for power, they take the dross of carbon dioxide and, with water and a scintilla of minerals, turn it into organic matter. Even better, as they work their combinatorial magic, they burp oxygen. Take a breath: At least 50 percent of the oxygen you inhale is made by algae. What is waste to them is priceless to all respiring animals. Without algae, we would gasp for air.

There is no shortage of algae. The oceans are blanketed in a dense but invisible six-hundred-foot-thick layer of them. Swallow a single drop of seawater, and you could easily down several thousand of these unseen beings. They are the essential food of the microscopic grazing animals at the bottom of the marine food chain. If all algae died tomorrow, then all familiar aquatic life—from tiny krill to whales—would quickly starve.

In fact, if algae hadn’t evolved 2.7 billion years ago and oxygenated the atmosphere, multicellular creatures would never have graced the oceans. It was a species of green algae that, 500 million years ago, acclimated to life on land and evolved into all of Earth’s plants. Without plants to eat, the first marine animals that wriggled out of the water 360 million years ago would never have survived or continued to evolve and diversify into all the land-living creatures we know today. If, several million years ago, our ancestor hominins hadn’t had access to fish and other algae-eating aquatic life—and thus to certain key nutrients—we would never have evolved our outsize brains. Without algae, we couldn’t know that all of life depends on algae.

Algae’s influence extends long after their death. Their microscopic, carbonaceous corpses—those that don’t become food for aquatic animals and bacteria—drift down through the ocean like a steady snowfall. On the ocean floor, they silently accumulate, their carbon remains sequestered for eons. By transferring carbon dioxide from the atmosphere to long-term storage, algae help keep our planet from becoming an unbearable hothouse. About fifty million years ago, when the Arctic was last ice-free year-round, a million-year burst of algae growth cooled the atmosphere to help create the icy conditions we see today.
Phycologists—scientists who study algae—have identified some 72,000 species, but there may be ten times as many yet to be named. Today, algae are in every earthly habitat, unseen under ice in Antarctica, blooming pink on the snows of the Sierra Nevada, in desert sand, inside rocks, on trees, and in the fur of three-toed sloths (who eat them). They live symbiotically inside corals, which cannot survive without their partners. Coral reefs are home to 25 percent of the world’s fish species and provide economic support to hundreds of millions of people. Now they’re dying at a shocking, heartbreaking rate because warming oceans disrupt the critical relationship between algae and their hosts.

So, what exactly are algae? There is no exact answer. Algae is not a precise term, not a taxonomic category like the kingdom Animalia or the genus Homo or the species Homo sapiens. Algae (and the singular alga) is a catchall term, a name for a group of diverse organisms. There are three types, in order of their evolution. The smallest, most ancient of them are the single-celled, internally simple blue-green algae, now generally known as cyanobacteria (or, more familiarly, cyanos). Next are the invisible, single-celled but internally complex microalgae. Together, cyanobacteria and microalgae are sometimes referred to as phytoplankton, from the ancient Greek, meaning “plant drifters.” Finally—and flavorfully—are the visible seaweeds, or macroalgae. Whether a cyanobacterium a tenth of the width of a human hair or a giant kelp more than 150 feet tall, algae share certain characteristics. Almost all of them photosynthesize, and the few species that don’t, once did.

Algae are also defined by what they are not. They are not plants, even though plants also photosynthesize. Until the twentieth century, algae were considered members of the kingdom Plantae. An understandable inclusion: many seaweeds look like plants, and colonies of microalgae growing on damp soil can look like mosses. Nonetheless, algae are fundamentally different from plants. They inhabit a kind of prelapsarian world where, floating in water with little or no effort, they bask in the Sun’s energy and bathe in water-borne nutrients that easily pass through their cell walls into their cytoplasm. You will never find algae dressed in flowers, wafting scents, or sporting seeds and berries. But because algae have no petals or nectar, no pistils or stamens, no bark to keep them from drying out, and no wood to hold them upright, they channel far more of the Sun’s energy into replication. They are dozens of times more productive than plants at making the carbohydrates, proteins, vitamins, and oils—as well as accumulating the minerals—that we value.

You can get algae’s nutritional benefits—especially their healthy omega-3 oils—directly by eating seaweeds. Every year, more than twenty-five million tons of seaweed, with a value of more than $6 billion, are harvested from gigantic watery farms in East Asia or plucked from the rocks off New England, Atlantic Canada, and northern European coasts. Seaweeds make up about 10 percent of Japanese and Korean diets, and their sales are growing worldwide. In the United States, various kinds of dried seaweeds are found on the shelves of grocery stores from Costco to Whole Foods, and they are sold just as widely in Europe. It’s easy to see why seaweeds are so popular: not only are many highly nourishing, many contain savory umami, one of the five basic tastes our tongues perceive.

Most of the algae we eat are macroalgae, but a number of companies are tinkering with microalgae and cyanobacteria, figuring out how best to process and market them for human consumption. Even if you don’t choose to eat algae directly, you may reap their nutritional benefit when you eat seafood. Wild sea animals that dine on algae accumulate algae’s omega-3 oils, so you benefit secondhand. But today, half the fish we eat are grown using aquaculture, where they are increasingly fed with corn and soy. Could we feed fish with microalgae and maintain their nutritional profile? A company in Brazil grows algae in steel vats for just that purpose.

Algae are a hidden part of our lives. You can find them in the kitchen: in ice cream to prevent ice crystals from forming, in chocolate milk to keep the cocoa suspended, in salad dressings to keep the components mixed, and in many other foods. Your tap water may have been filtered at the water treatment plant with live algae that remove nitrogen and phosphorus or with fossil algae that strain out particulate matter. Your fruits and vegetables may have been grown in soil supplemented with algae. You can find algae in the bathroom, where they thicken your lotions, keep your hair conditioner emulsified, gel your toothpaste, and coat your daily tablets. And you can now wear algae on your feet: a Mississippi company is making the soles of running shoes from pond scum.

Florida has been particularly hard-hit in recent years by algae “blooms,” as seen in 2016 under the Ocean Boulevard Bridge to Sewell’s Point in Martin County near Port St. Lucie.

As useful as algae can be, there can be too much of a good thing. In our era of global warming and unabated fertilizer runoff, rampant algae overgrowth is taking over more of our lakes and bays. Some of these algae “blooms” are merely unsightly, but others poison animals, including us. Florida has been particularly hard-hit in recent years. In 2018, the governor declared a state of emergency in seven counties as millions of dead fish washed up along the Gulf Coast and hospital visits for respiratory illnesses caused by airborne toxins jumped 50 percent.

Algae needn’t produce toxins to kill. Indirectly, they create aquatic “dead zones,” areas with little dissolved oxygen where nothing can live. There are now more than four hundred major dead zones around the world, covering tens of thousands of square miles, and they’re expanding every year.

Algae’s ability to multiply threatens lives and livelihoods, but can we somehow harness that prodigious productivity for the benefit of the environment? Like firefighters who create back burns to fight forest fires, a Florida company is battling a plague of algae with more algae. As the world’s vehicles, factories, and power plants continue to pour carbon dioxide into the atmosphere, there may be a role for algae in that cleanup as well. Algae are scarcer in the Southern Ocean than in the others; scientists are investigating how we might expand their numbers and thereby pull more carbon dioxide from the atmosphere and sequester it on the ocean floor. 

While there are few reasons to feel hopeful about the environment, the power of algae is one of them. Algae certainly will plague us in ever-increasing numbers, but still they are a source of hope. They can help remediate the waters we pollute. And, if push comes to calamitous shove, as the climate warms, iron-supplemented  algae may help scrub an atmosphere overloaded with carbon dioxide.

In May 2018, researchers led by Uwe Arnold at the Technical University of Munich published their work on a low-cost technique for converting algae grown with flue gas into lightweight, flexible-but-strong carbon fibers. The fibers, increasingly used in aircraft, vehicles, and construction to replace steel, aluminum, and concrete, are currently made from petroleum using processes that have a heavy carbon footprint. Carbon fibers are extremely durable, so if we can make them from algae, we can lock up CO2 for millennia. 

Algae can yield more biofuel per acre than plant-based biofuels—about 1,500 gallons of fuel per acre, per year—and is similar in composition to today’s transportation fuels. ExxonMobil and Synthetic Genomics in La Jolla, CA have a basic research program to develop advanced bio-fuels from algae.

Algae store energy as oil, much as potato plants store their energy as sugar in tubers. For about ten years now, scientists and engineers have been growing algae in artificial ponds, harvesting their oils, and converting them into transportation fuels. The U.S. Navy has already powered ships and planes with algae fuel. The price of algae is falling, but it is still too high to compete with subsidized fossil fuels. However, new bioengineering, harvesting, and conversion technologies can reduce production costs. Because about 12 percent of CO2 emissions from transportation comes from jets, algae jet fuel would have a significant impact in slowing climate change.

The European Synchrotron Radiation Facility reported in Science in September 2017 that a team of international researchers have discovered an enzyme in Chlorella that allows it to convert some of its fatty acids into hydrocarbons using only light energy. And, in November 2018, Japanese researchers reported the discovery of a “switch” that controls an alga’s ability to accumulate starches. By inactivating a certain enzyme, the researchers boosted the rate of accumulation tenfold. Both developments could lead to major advances in biofuels.

Beef cattle eating bull kelp on the beach on King Island (Tasmania). Adding kelp to the feed to ruminant livestock significantly reduces levels of methane.

Animal scientists have discovered that adding a soupçon of seaweed to the feed of ruminant livestock—cows, sheep, and goats—reduces levels of methane. The planet’s 2.5 billion farm ruminants emit methane that, according to the Food and Drug Administration, is equivalent to 7.1 billion tons of carbon dioxide per year. That’s nearly 18 percent of man-made carbon dioxide emissions—as much as we put into the atmosphere from burning transportation fuel.

Methane production starts in an animal’s first stomach chamber (its rumen), where bacteria ferment the tough carbohydrates in grasses. For years, scientists have been looking for feed additives that would prevent the bacteria from producing the gas, but until recently, nothing worked, at least not for long. Cows or their bacteria adapted to every new additive. About ten years ago, scientists at James Cook University in  Australia began experimenting with adding seaweed to cows’ feed to see if they could reduce methane emissions. While all the seaweeds they tested had a positive effect, the high dosages required upset the bovines’ digestion. Then the scientists tried Asparagopsis taxiformis, a macroalgae that looks something like a pink underwater fern. In the lab, adding just a little of this seaweed—2 percent of feed—to artificial cow stomachs reduces methane output so much that it becomes virtually undetectable.

The magic is performed by bromoform (CHBr3), a compound in seaweeds that protects them from bacterial infection. Bromoform also prevents methane-producing bacteria from completing the final step in digestion that creates gas. In experiments in Australia, sheep fed a little Asparagopsis produced 85 percent less methane. Preliminary reports from experiments at the University of California, Davis indicate that cows fed a diet  that includes just 1 percent seaweed produce 50 percent less methane, and the reduction is immediate. And taste-testers perceived no difference between samples from cows fed with and without seaweed.

Asparagopsis could be a big win for the environment. It also may be a win for animal farmers. Because cows expend energy to manufacture methane, animals fed Asparagopsis have more calories to direct to making proteins or milk, compounds that are more useful to their growth and our nutrition.

The seaweed could also be a win for developing countries. No one yet cultivates it, but the researchers expect it can be grown on long lines, much as carrageenan farmers in East Asia cultivate Eucheuma cottonii. A new seaweed industry would be a major economic benefit for Indonesia, the Philippines, and other tropical countries. And, if the seaweeds are grown where fertilizer runoff now feeds algal blooms and creates dead zones, they could help remediate those waters by soaking up the excess nutrients. It’s early days yet, but Asparagopsis is promising.

“The Dutch Weed Burger is a 100% plant-based hamburger, with seaweed as THE tastemaker,” according to the company’s founder, Lisette Kreischer.

Algae has long been a part of the human diet, and we’ll be eating more of it in the future—and not just as seaweeds. Companies may start investing in algae as an animal protein substitute. Growing animals for food is a remarkably inefficient way of nourishing people: Large animals eat many times the plant protein that they ultimately yield in meat. According to David Pimentel, professor emeritus at Cornell University, if all the grain currently fed to livestock in the United States were instead consumed directly by humans, we could feed nearly 800 million people. The good news is that the market for “faux meat” is expanding. Nestlé predicts that by 2020, $5 billion of plant-based meats will be sold in the U. S.; Tyson Foods forecasts that by 2045, 20 percent of meat products sold in the U. S. will be plant-based. While plants are currently the source of most of the protein in these products, algae—which produce protein even more efficiently and with far less impact on the environment—can be a part of the story.

Proteins are not just for eating. Every year, pharmaceutical companies create tens of billions of dollars’ worth of “recombinant pharmaceuticals,” protein-based drugs that are produced in laboratories by genetically altered cells. The cells—once primarily E. coli bacteria but increasingly mammalian cells—have added genes that instruct their natural protein-making machinery to express foreign proteins. These recombinant drugs include vaccines and medications that treat cancer, hormone deficiencies, and autoimmune and viral diseases. Some 400 recombinant protein-based drugs are currently used in medical treatments and nearly 1,500 are under development. 

Neither bacterial nor mammalian cells, however, are ideal factories for making all proteins. While bacteria are easily engineered and efficiently produce many simple, small proteins, they lack the sophisticated assembly processes of eukaryotes. The problem is that proteins are made of amino acids that are bonded, coiled, and folded into complex three-dimensional structures, and bacteria can’t perform all the steps to form the most elaborate shapes that humans need. On the other hand, while mammalian cells are capable of translating genetic instructions into the most sophisticated proteins, they are slow to reproduce and finicky about their living conditions, which makes large-scale production difficult and expensive. The average annual price of monoclonal antibody therapies made from mammalian cells is $100,000. In addition, using mammalian cells entails the risk of introducing cancer-causing gene sequences and infectious virus particles into the medication.

Several companies are looking to microalgae as an additional production platform. As eukaryotes, they have those advanced protein-making mechanisms that mammalian cells have, but they are less fussy, reproduce quickly, and they can’t be infected with human pathogens. Bioengineers don’t target the DNA in their nuclei, but in their chloroplasts; chloroplasts have the simple, circular chromosomes bequeathed to them by their cyanobacterial ancestors. In sum, in microalgae bioengineers get the best of all worlds: less complicated prokaryotic genes to alter with sophisticated eukaryotic machinery to translate genetic instructions into complex proteins.

A few companies are now working to make cheaper, safer, algae-based recombinant drugs. San Diego-based Triton Algae Innovations, Ltd., funded in part by a grant from the National Science Foundation, has created green algae that make a colostrum-like protein with the unique properties of human breast milk, which could be incorporated into infant formula. Lumen Bioscience, a Seattle startup supported with a grant from the National Institutes of Health, is working on an oral malaria vaccine that can tolerate higher temperatures, a useful property in countries where refrigeration is not always available. The list of recombinant protein medications in production grows daily; microalgae may be able to reduce their cost dramatically.

Algae. When you hear the word, you’ll certainly still think of pond scum. Algae blooms are growing ever larger and lasting longer, threatening health and livelihoods. But I hope you’ll also think of the world’s most powerful engines, the sun-powered green dynamos that constantly convert a noxious gas and water into the valuable stuff of life. I hope that from time to time you’ll recall (using your algae-bolstered brain) how algae created—and constantly refresh—our oxygen-rich atmosphere. Remember that every fish in the sea depends on algae and that every plant on land is a sophisticated alga.

There will be no single, quick fix to our intertwined environmental crises, and it will take many small measures that have a significant effect in the aggregate. A 10 percent reduction in carbon dioxide emissions here; a 15 percent reduction in methane emissions there; a 5 percent drawdown of atmospheric carbon in the future—pretty soon you’re talking about real environmental relief. 

Algae: They created us, sustain us, and, if we’re both clever and wise, they can help save us.


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These sun-powered green dynamos are so much more than pond scum.