David Wallechinsky - The Book of Lists

This common black mould, most often found on rotting vegetation, played a key role in the collapse of a major industry. Until the early 1920s, Italy produced about 90% of the world’s citric acid, using low-grade lemons. Exported mainly to the US as calcium citrate, this citric acid was a costly ingredient — about a dollar a pound — used in food, pharmaceutical and industrial processing. When American chemists discovered that A. niger , the most ordinary of moulds, secreted citric acid as it grew in a culture medium, they seized the opportunity to perfect citric-acid production using the easily grown mould. Charles Pfizer & Co., of Brooklyn, New York, became known as the ‘world’s largest lemon grove’ — without a lemon in sight. Hardworking acres of A. niger were soon squirting out such quantities of citric acid that by 1923 the price was down to 25¢ per pound and the Italians were out of business.

A purplish-black, spur-shaped mass, C. purpurea is a formidable and even frightening fungus that has long plagued mankind. But in addition to its horrible effects, C. purpurea also has valuable medical uses if the greatest care is taken to use tiny amounts. The fungus is a powerful muscle contractor and can control bleeding, speed up childbirth and even induce abortion. It is also the source of the hallucinogenic LSD-25. In doses larger than microscopic, C. purpurea — commonly called ergot — produces ergotamine poisoning, a grisly condition known in the Middle Ages as St Anthony’s fire. There is still no cure for this hideous, often fatal disease caused by eating fungus-infected rye. The victim suffers convulsions and performs a frenzied ‘dance’. This is often accompanied by a burning sensation in the limbs, which turn gangrenously black and fall off. Some victims of medieval ergotism went insane and many died. In AD994 more than 40,000 people in two French provinces died of erogotism, and in 1722 the powerful fungus forced Peter the Great of Russia to abandon his plan to conquer Turkey when, on the eve of the Battle of Astrakhan, his entire cavalry and 20,000 others were stricken with ergotism. The last recorded outbreak of ergot poisoning was in the French village of Pont-Saint-Esprit in 1951.

The humble bread mould N. crassa provided the means for scientists to explore the most exciting biological discovery of the twentieth century: DNA. As anyone with an old loaf of bread in the bread box knows, N. crassa needs only a simple growing medium and it has a short life cycle. With such co-operative qualities, this reddish mould enabled George Beadle and Edward Tatum to win the Nobel Prize in Medicine/Physiology in 1958 for discovering the role that genes play in passing on hereditary traits from one generation to the next. By X-raying N. crassa , the researchers produced mutations of the genes, or components of DNA, and then found which genes corresponded with which traits.

A few dots of a rather pretty bluish-green mould were Dr Alexander Fleming’s first clue to finding one of the most valuable lifesaving drugs ever developed. In 1928 he noticed that his petri dish of staphylococcus bacteria had become contaminated with symmetrically growing, circular colonies of P. notatum . Around each speck, all the bacteria were dead. Fleming further found that the mould also killed pneumonia, gonorrhea and diphtheria germs — without harming human cells. The unassuming bluish-green mould was beginning to look more interesting, but Fleming could not isolate the active element. Not until 1939 did Howard Florey and Ernst Chain identify penicillin, a secretion of the growing mould, as the bacteria-killer. The first important antibiotic, penicillin revolutionised treatment of many diseases. Fleming, Florey and Chain won the Nobel Prize in Physiology/Medicine in 1945 for their pioneering work with the common fruit mould that yielded the first ‘miracle drug’.

According to an old legend, a French shepherd forgot his lunch in a cave near the town of Roquefort and when he found it weeks later, the cheese had become blue-veined and was richly flavoured. No one knew why this happened until American mycologists discovered the common blue mould P. roquefortii in 1918. All blue cheeses — English stilton, Italian gorgonzola, Norwegian gammelost, Greek kopanisti and Swiss paglia — derive their tangy flavour from the energetic blue mould that grows rapidly in the cheese, partially digesting it and eventually turning the entire cheese into mould. Of course, it’s more appetising to say that P. roquefortii ripens the cheee instead of rotting it, but it’s the same process.

The political history of the world changed as a result of the unsavoury activity of P. infestans , a microscopically small fungus which reduced Ireland to desperate famine in 1845. Hot, rainy July weather provided perfect conditions for the white fungus to flourish on the green potato plants — most of Ireland’s food crop — and the bushes withered to brown, mouldy, stinking clumps within days. The entire crop was devastated, causing half a million people to starve to death, while nearly two million emigrated, mostly to the United States. P. infestans dusted a powdery white death over Ireland for six years. The fungus spread rapidly and just one bad potato could infect and ruin a barrel of sound ones. British Prime Minister Robert Peel tried to get Parliament to repeal tariffs on imported grain and while the MPs debated, Ireland starved. Relief came so slowly and inadequately that Peel’s government toppled the next year, in 1846.

A soft, downy mildew infecting American-grown grapes was responsible for nearly ruining the French wine industry. In 1872 the French unwittingly imported P. viticola on grafting stock of wine grapes grown in the United States. Within 10 years, the mild-mannered mildew had quietly decimated much of France’s finest old vineyards. But in 1882 botanist Pierre-Marie-Alexis Millardet discovered a miraculous cure for the ravages of P. viticola . He noticed that Médoc farmers painted their grape leaves with an ugly paste of copper sulphate, lime and water — to prevent theft. Called Bordeaux mixture, this paste was the first modern fungicide. The vineyards of France recovered as the entire world sighed with relief.

9. MERCHANT OF DEATH ( Saccharomyces cerevisiae )

Ordinary brewers’ yeast, S. cerevisiae , used to leaven bread and make ale, was once employed as a wartime agent of death. During WWI, the Germans ran short of both nitroglycerin and the fat used in its manufacture. Then they discovered that the usually friendly fungus S. cerevisiae could be used to produce glycerin, a necessary ingredient in explosives. Fermenting the fungus together with sucrose, nitrates, phosphates and sodium sulphite, the Germans produced more than 1,000 tons of glycerin per month. According to some military sources, this enabled them to keep their war effort going for an additional year.

A lowly mould found in dirt and manure piles, S. griseus nevertheless had its moment of glory in 1943, when Dr Selman Waksman discovered that it yields the antibiotic streptomycin, which can cure tuberculosis. Waksman went to the United States in 1910 as a Russian refugee and by 1918 he had earned his doctorate in soil microbiology. He had worked with S. griseus before, but not until a crash programme to develop antibiotics (a word coined by Dr Waksman himself) was launched did he perceive the humble mould’s possibilities for greatness. Streptomycin was first used successfully on human beings in 1945, and in 1952 Dr Waksman was awarded the Nobel Prize in Physiology/Medicine.