Ingestion / What Is Fusarium?

“Ingestion” is a column that explores food within a framework informed by aesthetics, history, and philosophy.

Fusarium is a widely distributed genus of soil-based fungi that, unlike mushrooms, does not form large fruiting bodies, prefering to grow in obscurity as it extends long, delicate filaments through the moist vegetative matter that feeds it. That is to say, Fusarium is a kind of mold. Given that most of this abundant genus is both harmless and invisible to the unaided eye, we are unaware of the fact that we frequently come in contact with it. Much like mushrooms, however, some species are noteworthy for producing highly specific poisons known as mycotoxins that can be spectacularly deleterious to human and animal health if they enter the food chain. In spite of its ubiquity and potential toxicity, Fusarium was not described until the early nineteenth century, and didn’t play a prominent role in the affairs of men. This changed in the twentieth century.

Thousands purportedly died from eating wheat contaminated with Fusarium sporotrichioides in the Soviet Union during the bitter springs of the 1940s. Totalitarianism, famine, and war not only contributed to the mass poisonings but also effaced them. What little is known is that after the forced collectivization of farms and during the war, when labor was scarce, farmers gleaned winter wheat that, under normal conditions, would have been discarded. This wheat had overwintered under the snow and had been subjected too often to thaw and frost, and had thus developed a crown blight that caused the heads to turn pink. Made into bread and distributed, the rotting grain caused a mortality rate estimated at 60%.^[1]

Alimentary toxic aleukia (the condition induced by ingesting Fusarium mycotoxins) is particularly awful. Once the acute, convulsive phase has passed, the symptoms are rather like radiation poisoning: first pain and vomiting, and then bleeding of the gums and digestive tract, and then your teeth slip painlessly, frictionlessly from your head as your white blood count falls towards zero.^[2] Death itself could take weeks. Although the poisonings were widespread, many were mistaken for typhoid and other concurrent epidemics. Stalin was not known for his transparency in matters of public health, and the exact number of fatalities remains uncertain.

Meanwhile, in the United States, Fusarium was responsible for a calamity of a more domestic scale. Starting in the early twentieth century, the widespread availability of bananas, a perishable tropical fruit, had stood as testament to the enormous economies of scale and organizational prowess of the United Fruit Company. In the overwhelming majority of cases, the banana on any given US kitchen table would have been a cultivar known as the Gros Michel, or “Big Mike.” The Big Mike was grown as a monoculture in massive plantations across Central America, under a vertically integrated business empire that controlled rail lines, fleets of refrigerated ships, and, ultimately, governments. Beginning in the 1920s, however, an untreatable fungal wilt known as Panama disease had begun to so affect the crop that availability became unpredictably constricted, and prices commensurably volatile. The 1923 hit song “Yes! We Have No Bananas” commemorated the shortages that accompanied the beginning of Big Mike’s demise. Panama disease, caused by Fusarium oxysporum, killed banana trees up and down the coast.^[3]

Once it has gained entry into the plant via the roots, Fusarium colonizes the vascular system, absorbs all the available nutrients, and, at the end of its reproductive cycle, utterly ruptures the circulatory system, leaving the plant to die of exhaustion. (In this respect, the relationship of mold to plant is not at all unlike the relationship of United Fruit Company to the Central American economies it dominated.) New plantations seeded amidst freshly cleared rainforest initially produced well, but soon after sickened and died. By the mid-1950s, the Big Mike was to all intents and purposes extinct.

The banana that replaced it, the Cavendish, had been cultivated in the Canary Islands for centuries, but was widely regarded as inferior. Smaller, duller and less tasty, its one grace was a resistance to Panama disease and it is now the ubiquitous variety. “Variety” is perhaps a misleading word. Like the Big Mike, the Cavendish is artificially reproduced through cuttings, and so every tree, and every fruit, is genetically identical. This makes the plantations extremely vulnerable to the co-evolution of parasites. In recent decades, Cavendish banana trees have also begun dying from a Fusarium wilt that appears to have originated on the island of Sumatra. There is no known way of chemically treating the disease, nor of containing its spread, and speculation has already begun as to when the last banana, as we know it, will be sold and eaten.

On the opposite side of the Atlantic, the identification of Fusarium sporotrichioides as the cause of the alimentary toxic aleukia pandemic was soon followed by the isolation of trichothecene as the lethal mycotoxin involved. Intrigued by its military applications, the Soviets had developed a flourishing biological weapons program around the mycotoxin when the Biological Weapons Convention came into effect in the early 1970s. From that point on, the use and even the possession of such weapons amounted to a serious violation of international law. The excretions of a fungus had gone from being merely toxic, to a weapon, to a potential protagonist in Cold War diplomacy. It was in this context that testimony from Hmong refugees fleeing from Laos and Cambodia proved particularly incendiary.

The Hmong reported that they had seen a poisonous yellow rain fall from the sky, a rain that burned the skin and caused its victims to vomit blood before convulsively dying. The numbers of reported deaths ranged into the hundreds, and the symptoms described fell within the broad spectrum of the Fusarium poisonings of the 1940s. Special teams were dispatched to collect evidence, and in 1981, the American secretary of state Alexander Haig, in an address to the Berlin Press Association, argued that the Soviet Union was supplying trichothecene-based chemical weapons to the Vietnamese, and that these weapons were being deployed in the ongoing war in South-east Asia. Most significantly, Haig was able to present physical evidence: samples of vegetation covered in hundreds of small, brightly colored yellow spots, up to five millimeters in diameter. These samples of “yellow rain” had tested positive to trichothecene in a laboratory at the University of Minnesota and constituted a veritable smoking gun.^[4]

Haig’s claim amounted to an accusation of a serious breach of international treaties. Such an accusation required corroboration, and samples of yellow rain were duly sent to independent laboratories around the world. A scientist in Britain, examining the samples under an ordinary optical microscope, was surprised to note that the yellow spots appeared to contain high quantities of pollen. The State Department called a press conference and announced that this new discovery only strengthened the case. Intelligence officer Gary Crocker is recorded as having said: “It contains pollen, and not windborne pollen, but pollen that would be commercially collected or is collected, if you will, by insects, the type of thing you would get in a—a honey bee would take from flowers. And they are the particular size. It happens to be the right size to be retained in the body.”^[5] The intelligence analyst Sharon Watson helpfully attempted to elucidate the significance of this:

Well I think I might just clarify a point, and that is the role of pollen in the mixture. The agent, as it comes down, is wet, and at this time the primary exposure appears to be through the skin, and the toxins are dissolved in the solvent, going through the skin very quickly. But as the agent dries, a secondary aerosol effect can be caused by kicking up this pollen-like dust that is of a particle size that will be retained in the bronchii of the lung. […] So if you could bring the compound into contact with the mucous membranes of the bronchii, then it’s a very effective way of getting it across. So there are two different ways that the compound is absorbed. It’s [a] very clever, clever mixture.^[6]

The subtlety and complexity of the alleged secret weapon was significantly increased when a scientist at the Australian Defence Scientific Service identified the pollen as belonging to trees native to South-east Asia, rather than being from flowers that might be found at a location where the Soviets were known to have an established chemical weapons program, such as Tashkent. The inflating complexity of the State Department’s argument induced the Harvard biochemist Matthew Meselson and the Yale entomologist Thomas Seeley to travel to Thailand to investigate in more detail. Searching for direct evidence of chemical weapons use near the village of Khua Moong, they found themselves caught directly in a shower of glistening lukewarm yellow droplets covering an area of several hundred square meters.^[7] There were no suspicious aircraft to be heard, or shell casings to be found, only a cloud of wild bees above the canopy. In an uncharacteristic moment of wry humor, the journal Nature later referred to these collective events as “brief but abundant defecation sorties” undertaken to cleanse the hive before the onset of the wet season.^[8] What resulted from the cleansing flights were dense swaths of yellow spots visually identical to the samples of “yellow rain” collected by US intelligence. And the trace levels of trichothecene? Well, aside from the possibility of cross-contamination in the Minnesota lab, Fusarium-afflicted sorghum is also a common problem in South-east Asia.

All this could be seen as a conventional tale of tragedy ending in farce, but it should be noted that an industrial application of Fusarium has been found, and not as poison, but as food. In the late 1960s, amid neo-Malthusian predictions of a bleak future of mass starvation and overpopulation, multinational bioscience and pharmaceutical companies turned their attention to the possibility of using single-celled organisms as a cheap source of protein. The science employed had its roots in zymotechnology, or industrial-scale fermentation, a technique that had been used to produce a kind of edible yeast-based slurry in Berlin during World War I. In 1989, the Soviet Ministry of Microbiological Industry had eight industrial plants associated with oil refineries that grew yeast in a substrate of paraffin.^[9] In general, however, the public relations challenge presented by edible bacteria grown in crude oil was held to be insurmountable, and so the majority of industrial-scale single-cell protein projects focused on producing cost-efficient animal feed.

A particular process developed by Imperial Chemical Industries known as “Pruteen” underwent extensive development before being abandoned as too costly.^[10] ICI did, however, bequeath one of their large vats, better known as an airlift fermenter, to the Rank Hovis MacDougall (RHM) research center. RHM, unlike other firms, had directed their attention to the high-margin business of producing food for humans. Their researchers were particularly interested in a strand of Fusarium that had been found growing in the dirt in a commuter village on London’s western periphery. It was non-toxic, easily grown in vitro, and high in chitin, the same protein that is found in insect exoskeletons. Out of this simple organism, RHM developed the textured meat-substitute known as Quorn. Ingeniously, instead of focusing on the microbial origins of Quorn, its manufacturers have successfully marketed it as a health food by emphasizing what it is not: meat.^[11] Flavorless and colorless, it can be easily processed to resemble other meats, including beef, chicken, and turkey. This talent for mimicry on the part of Fusarium is chiefly thanks to the shape of its hyphae—the long fibrous strands that it forms, the same strands that make it so deadly to the banana, resemble in diameter and length the muscle fibers of animals. With appropriate binders, the hyphae can be induced to form a kind of mat of interconnecting fibers, which allow it to take on the texture of meat. Emblazoned with the Vegetarian Society’s seal of approval, Quorn is now the most popular ersatzfleisch in the UK. Although the marketing material prevaricates over whether to treat Quorn as akin to a mushroom or a yogurt, it is a sterile, nutritious Fusarium mold.

The author wishes to thank Dr. Brett Summerell of the Royal Botanical Gardens, Sydney.