Fungal Futures: Ancient Egyptians, Cats, and Wonder Bread

My recent distraction from dissertation writing, concerns how we can use fungi as biocontrols to improve agricultural sustainability. Increased study in recent years shows that even the most well-characterized fungi have a new story to tell. One fungus stands above the rest not only for its foundational role in both basic and applied sciences, but also for its deep ties to human civilization. Please give a hearty welcome for our guest: Saccharomyces cerevisiae.

In this post I discuss a brief, meandering history of biocontrol in agriculture and an emergent partner in our quest to feed billions of people. More than anything though, this post is inspired by S. cerevisiae wheat elixir, otherwise known as beer.

An Egpytian painting depicting a cat killing a large snake with a blade.

Using one organism to control the populations of another organism, or biological control, is an ancient practice in human agriculture reaching back to 2,000 BCE where Egyptians allied with cats to control rodent/pest populations. I say ‘allied’ and not ‘domesticated’ because it’s not entirely clear if we actually domesticated cats, or if cats domesticated themselves. Either way, the path to an inter-species partnership was likely spurred by expansions of agriculture coinciding with the transition from hunter-gathering communities to large-scale farming operations. Large-scale agriculture is considered a major milestone in human civilization as formerly nomadic peoples began settling in fertile regions to cultivate monocultures of choice varieties. Food surplus promoted population expansion however, like a great 21st century poet declared, my agricultural milkshakes brings all the rodent boys to the yard. And indeed! Stores of grain are the ultimate milkshake for rodents.

The arrival of rodents and switch from nomadic to stationary lifestyles likely increased disease incidence in human settlements yet, as with all great stories, a hero emerged. Slinking from fields wielding 10 cosmic blades blessed by the ancestors of old, this hero was small in stature, nimble, and fierce. Our hero: the great domestic cat. These ancestors to modern day domestic cats served as agricultural sentinels by predating on the budding rodent population. In return for their rodent control services, cats became revered as holy symbols receiving plentiful food and, in some cases, palaces of their own. While cats ruled, they were not the only symbiotic hero amidst the Ancient Egyptians. Cue everyone’s favorite fungus, yeast.

Ancient Cervezas

“Civilization begins with fermentation” — William Faulkner

For the uninitiated, yeasts are fungi — a fact that eluded me for longer than I care to admit (I started in Chlamydia!). Yeasts are single-celled Eukaryotes differentiated from Prokarotes by the presence of organelles and genetic material enclosed a nucleus. These miraculous microbes represent one of the most important fungal partners in human history due to their ability to convert sugars to CO2 and alcohol through the process of fermentation. Ancient Egyptians utilized fermenting yeasts to produce their hallmark beer by crumbling half-baked bread into wheat and barley slurries. The resulting product called "heqnet" was a staple beverage for the Egpytians used for a variety of cultural ceremonies, however, our interest is pragmatic: by increasing the alcohol content in the slurry to become inhospitable to disease-causing microbes, Egpytians, and cultures around the world, could produce safe-to-drink water with their fungal partner. While it is unclear which yeast species produced ancient beer, the use of bread as a starter for fermentation implicates Baker’s yeast, known in the scientific literature as Saccharomyces cerevisiae.

Wonder Bread Fungus

S. cerevisiae’s ability to tolerate high-sugar environments and convert those sugars into gourmet products is just one of its many talents. The fungus is increasingly recognized for its uses as an agricultural amendment and biocontrol of agricultural disease-causing agents (Ali et al., 2024). As an example, a 2008 study from researchers in Egypt (Shalaby & El-Nady, 2008) (we’re coming full circle now) applied yeast extracts to the seedlings, leaves, and soil of beet plants to test the effects of seedling germination and bioactivity against the fungal pathogen of beets, Fusarium oxysporum.

Two bar plots side by side comparing the effects of S. cerevisiae on seedling germination % and the inhibition of three common plant pathogens.

At its core, the study demonstrates the utility of S. cerevisiae in agriculture through both a bio-stimulant effect and for its bioactivity against of phytopathogen F. oxysporum. I have one last example to bring us full circle: In a 2014 study of wheat, Egyptian researchers (Hammad & Ali, 2014) tested yeast extract as mechanism to increase the plant’s tolerance to drought conditions. Their study is fascinating in their findings that wheat can be ‘rescued’ from the effects of extreme drought conditions when treated with S. cerevisiae extract.

Graph that plots the increasing number of publications (left, y-axis) and citations (right-y-axis) since 1995 of studies concerning “biocontrol” and “S. cerevisiae”.

Fungal Futures of S. cerevisiae

A quick search on Web of Science using the key words “S. cerevisiae” and “biocontrol” underscores recency of our explorations in this realm with the mentioned studies representing some of our earlier endeavors. I could go on about how researchers are testing S. cerevisiae with a variety of plants from cucumbers to potatoes, each time revealing that this little yeast knows its way around a plant but your time is precious and my own heqnet provisions are running low.

Advancements in synthetic biology and bioengineering of fungi open the door to ask how we can manipulate these fungi to further enhance their biocontrol applications. I will try and discuss these advancements in the future but, no matter where these yeasts take us, they will always find a home in my refrigerator. Ultimately, the rise in both the number of studies and their citations in recent years for just this species indicates, to me, that the fungal renaissance has taken hold and we are certainly better for it. While our history with S. cerevisiae is ancient, I hope you leave with an appreciation for the impending age of fungal biotechnology.

References

Ali, A., Ölmez, F., Zeshan, M. A., Mubeen, M., Iftikhar, Y., Sajid, A., Abid, M., Kumar, A., Divvela, P. K., & Solanki, M. K. (2024). Yeast-based solutions in controlling plant pathogens. Biocatalysis and Agricultural Biotechnology, 58, 103199. https://doi.org/10.1016/j.bcab.2024.103199

Hammad, S. A. R., & Ali, O. A. M. (2014). Physiological and biochemical studies on drought tolerance of wheat plants by application of amino acids and yeast extract. Annals of Agricultural Sciences, 59(1), 133–145. https://doi.org/10.1016/j.aoas.2014.06.018

Shalaby, M. E.-S., & El-Nady, M. F. (2008). Application of Saccharomyces cerevisiae as a biocontrol agent against Fusarium infection of sugar beet plants. Acta Biologica Szegediensis, 52(2), Article 2.