Microbiology beyond the micrometer

by Reed Stubbendieck (@bactereedia)

Figure 1. Light Microscope from the late 1800s. Photo credit: Reed Stubbendieck, Personal Collection.

If I asked you what the signature tool of a microbiologist is, you would likely respond: the microscope (Fig. 1). Not only do the field and instrument share the prefix micro (from Greek mikrós, meaning “small”), but the development of microscopy established the field of microbiology. In the mid-seventeenth century, Robert Hooke and Antonie van Leeuwenhoek built the first microscopes. Using his microscope, Hooke provided the first description of a microorganism when he reported on the fruiting bodies of fungi and coined the term “cell” in reference to the structures that he observed in cork. Meanwhile, van Leeuwenhoek was the first individual to observe protozoa and bacteria, which he called “wee animalcules”.

Born from the observations of Hooke and van Leeuwenhoek, generations of microscopists have used the microscope to study the structure and substructures of cells, observe proteins in motion, and diagnose diseases, among many more applications (Some of which I’m sure Scott will explore in future posts). Thus, since the inception of microbiology, it has been difficult to disentangle the field and the instrument. However, microbes are not confined to the micrometer scale and hidden beyond our eyesight. In this post, I would like to highlight some examples of microbes that you likely encounter in your daily life and are visible with your naked eye.

Figure 2. Mushroom fruiting bodies. Photo taken in East-Central Texas by Reed Stubbendieck.

Some of the most obvious examples of macroscopic microbes are fungi and include the beautiful mushrooms that bloom near the trunks of trees in our yards and forests (Fig. 2). But given that antibiotics are one of my primary research interests, I’d be remiss if I didn’t highlight the humble bread mold Penicillium. Who among us hasn’t kept a loaf of bread for a little too long, only to discover an unexpected fuzzy blue-green growth (Fig. 3A)? Likely, we write off the loss, toss the loaf, and head to the grocery store to acquire more bread. However, this contaminant is among the most important microbes ever discovered! In 1928, spores from this mold contaminated a Petri plate in Alexander Fleming’s laboratory and produced a region where bacteria were unable to grow (called a “zone of inhibition”) (Fig. 3B). Later on in 1940, Fleming’s observations inspired the chemists Ernst Chain, Howard Florey, and Norman Heatley to develop methods to mass produce the active agent from the mold. The result of their work was the antibiotic penicillin (Fig. 3C), which was likely the single most important advancement in modern medicine. Not a bad cost for a missed sandwich.

Figure 3. The bread mold Penicillium produces antibiotics. (A) Moldy bread covered in Penicillium. Note: this is a stock photo and not a picture of my own bread (B) Penicillium inhibits the growth of the pathogen Staphylococcus aureus on Petri plates. (C) Core structure of penicillin. The R group is variable and distinguishes different types of penicillins. Photo credits: Panel A: Wikipedia user Henry Mühlpfordt  under the GNU Free Documentation License, Version 1.2. Panel B: Christine L. Case, Ed.D.

While antibiotics treat our infections, the yeast Saccharomyces cerevisiae helps feed the body and soul. To simplify an introductory course in biochemistry, when yeast consumes sugars but is starved for oxygen, it produces carbon dioxide gas and ethanol as byproducts of its metabolism. We use the former to make our bread rise and the latter to give our booze its buzz (Fig. 4A). But that’s not all, together the interactions of yeast and bacteria give sourdough bread its signature tangy acidic taste (Fig. 4B), form the biofilms that make up the rinds of cheese (Fig. 4C), and provide starters for Kombucha tea (Fig. 4D) (see here for more information).

Figure 4. Fermented beverages and foods. (A) Homebrewed wheat beer in fermenter showing Krausen, the foamy head that consists of yeasts and wort protein, at the air-liquid interface. (B) Sourdough starter showing carbon dioxide bubbles after feeding. (C) The rinds of cheese wheels are a mixed bacterial and fungal biofilm. (D) Kombucha tea with pellicle at the air-liquid interface. Photo credits: Panels A and B: Reed Stubbendieck. Panel C: Wikipedia user Myrabella under a CC BY-SA 3.0 license. Panel D: Graciously provided by anonymous.

Outside the kitchen, microbes also live together symbiotically and produce amazing structures. For example, the lichens that cover rocks, tree trunks (Fig. 5A) and gravestones (Fig. 5B) are made up of algae, cyanobacteria, ascomycete fungi, and even yeasts living together! Within nature, symbiosis is the name of the game.

Figure 5. Lichens. (A) Lichen covering a tree trunk in Wisconsin. (B) Lichens growing on a gravestone. Photo credits: Panel A: Reed Stubbendieck. Panel B: Brian Robert Marshall under a CC BY-SA 2.0 license.

One of my favorite symbiotic systems is studied by my current laboratory and involves  fungus farming ants, the fungus they cultivate (called the cultivar), and a symbiotic bacteria called Pseudonocardia. These ants cut leaves and other plant material (depending on the ant species), but the ants do not eat the leaves. Instead, the ants feed the leaves to their fungal crop, which they consume it as their sole food source. Because the fungal cultivar is maintained asexually with limited opportunities for genetic recombination, it is not genetically diverse and is susceptible to pathogen infection. One pathogenic fungus is called Escovopsis and it is only found within the fungal gardens. The Escovopsis can overgrow and consume the fungal crop. To prevent this infection, the ants use grooming behaviors and form a symbiotic relationship with bacteria called Pseudonocardia, which produces antifungals that inhibit the growth of Escovopsis but are not harmful towards the fungal cultivar. The ants have evolved specialized structures to house and feed the Pseudonocardia on their exoskeletons and some ants, such as Acromyrmex sp. cf. octospinosus, can become totally covered by their symbiotic bacteria (Fig. 6)!

(Note, I will almost certainly cover the relationship between fungus-farming ants and Pseudonocardia in more detail in a future post.)

Figure 6. Symbiosis between ants and bacteria. Acromyrmex sp. cf. octospinosus worker ant covered in white symbiotic bacteria. Note the chewed leaves in the fungal crop. Photo credits: Alex Wild, purchased for use on this website.

Finally, should you find yourself in orbit over Earth, please find comfort in the knowledge that you can still revel in the beauty of our microbial world. Satellite photographs from NASA have captured images of massive blooms of algae in our planet’s oceans and seas!

Figure 7. Algae bloom over the Barents Sea. This photograph showing a large algal bloom was taken by the NASA Aqua satellite in 2011.

This post has barely covered the diversity of microbes in our world, but I hope it has convinced you to leave the microscope behind and look for examples of microbes in your daily life. Check your showers for the pink-colored Serratia marcescens, observe a lovely mushroom on your lawn, or  overturn a rock and find a lichen. I would love for you to share your pictures with me! Use the hashtag #macromicrobiology and be sure to tag @bactereedia and @SciSidequests in your post.


If you’re interested in checking out more beauty in the microbial world, I highly recommend the book Life at the Edge of Sight by Scott Chimileski and Roberto Kolter and the corresponding museum exhibit at the Harvard Museum of Natural History.