Differences and Similarities Between Bacteria and Fungi

Bread goes moldy. Milk turns sour. Both are the work of microorganisms you cannot see, yet the fuzzy green patch on the bread and the invisible souring of the milk come from two completely different kinds of life. The mold is a fungus. The souring is done by bacteria. They look similar under a hand lens and share a few habits, which is exactly why students keep asking whether a fungus is just a kind of bacterium.

It is not. A bacterium and a fungus are as different from each other as a bacterium is from you. The clearest way to see this is a single fact that drives almost everything else: bacteria are prokaryotes, and fungi are eukaryotes. Once you understand what that one difference means, the rest of the table below stops being a list to memorize and starts making sense on its own. And it explains something with real consequences: why an antibiotic that wipes out a bacterial infection does absolutely nothing against a fungal one.

Bacteria are microscopic unicellular organisms found almost everywhere on the Earth. These are critical for ecosystems as they effortlessly recycle nitrogen, carbon, and sulfur. These can also cause harmful diseases to humans, animals, and plants. Some bacterial species can grow in extreme conditions like high temperature, low pH, and high pressure.

Fungi are microscopic unicellular or multicellular organisms. Most fungi inhabit soil and dead organisms and play a crucial role in mineralizing organic carbon. Fungi are opportunistic pathogens. But mainly, these decay and decompose food, dead animals, and plants.

The significant difference between bacteria and fungi is their cell; bacteria are prokaryotes, and fungi are eukaryotes. In addition, bacteria and fungi have differences in their growth requirements, cell wall components, size, morphology, colony characteristics, and treatment methods.

Although bacteria (Monera) and fungi (Mycota) have many differences, they have similarities as well. Both have a true cell wall and many beneficial roles in nature, and some species of each can cause serious disease. The rest of this article walks through where they overlap, where they differ, and why those differences matter when you are trying to identify one in the laboratory or treat an infection caused by one.

Figure: Bacteria and fungi under microscope

Similarities Between Bacteria and Fungi

• Both are microscopic. A single bacterium or a single fungal yeast cell cannot be seen with the naked eye, though a fungal colony or a mold mat certainly can.
• Both have a true, rigid cell wall. The building material is different. Bacteria use peptidoglycan; fungi use chitin, and sometimes cellulose or other polysaccharides. What they share is the principle: an external wall that gives the cell its shape and protects it from bursting. This shared feature is why both stain and behave differently from animal cells, which have no wall at all.
• Both are heterotrophs. Neither can make its own food the way a plant does. Both must take in organic carbon from their surroundings, which is why both are found wherever there is dead or living organic matter to feed on.
• Both include beneficial species. Among bacteria, Lactobacillus is used as a probiotic, Staphylococcus epidermidis forms part of the protective normal flora of the skin, and gut Escherichia coli helps its host. Among fungi, baker's and brewer's yeast (Saccharomyces cerevisiae) raises bread and ferments alcohol.
• Both include serious pathogens. Bacteria cause cholera (Vibrio cholerae) and typhoid (Salmonella enterica serovar Typhi). Fungi cause invasive disease too, such as an aspergilloma (fungus ball) formed by Aspergillus species in a damaged lung.
• Both can live as saprophytes or as parasites. Many environmental bacteria and most fungi are saprophytes, living on dead organic matter. Others are parasites that live on or in a host.
• Both need moisture, nutrients, and a suitable temperature to grow. This is why both spoil food, and why keeping food dry, cold, or sealed slows both of them down.

Difference Between Bacteria and Fungi

How to Remember

"Pro-fun": Bacteria are Prokaryotes, Fungi are eukaryotes. The word fungi contains the sound "eu-" if you say it as "eu-fun-gi." A slightly silly hook, but the pairing that matters (fungi = eukaryote) is the one students most often reverse, so anything that locks it in is worth using.

The wall tells the drug story. If you remember only one row, remember the cell wall. Bacteria build their wall from peptidoglycan, which is what penicillin attacks. Fungi have no peptidoglycan, so penicillin is useless against them; fungi are hit instead through ergosterol in their membrane. "No peptidoglycan, no penicillin" is the whole reason antibiotics and antifungals are separate drug cabinets.

Endospore versus spore, in one line: a bacterial endospore is a bunker (built to survive, then go back to being one cell), while a fungal spore is a seed (built to reproduce and spread). Same word "spore," opposite jobs.

Where Students Get Confused

"Is a fungus a type of bacterium?" No. This is the most common beginner question, and the answer is a firm no. They sit on separate branches of life. A bacterium is a prokaryote with no nucleus; a fungus is a eukaryote with a true nucleus, more closely related to plants and animals than to bacteria.

Bacterial endospore versus fungal spore. Both use the word "spore," so students assume they are the same. They are opposite in purpose. Only a few bacterial genera (such as Bacillus and Clostridium) form an endospore, and only to survive heat, drying, or starvation; the endospore later germinates back into the same single cell. Fungal spores are the normal way many fungi reproduce and spread to new places. Survival capsule versus reproductive seed.

"Why are fungi bigger than bacteria?" Because a eukaryotic cell is inherently larger and more complex than a prokaryotic one. It carries a nucleus and organelles that a bacterium does not have, so it needs more room.

Why antibiotics do not treat fungal infections. Antibacterial drugs are built to attack features bacteria have and fungi do not: the peptidoglycan wall and the 70S ribosome. Fungi have neither, so the drug has nothing to grab. Treating a fungal infection needs an antifungal, which targets ergosterol or chitin instead. Giving an antibiotic for a fungal infection does not work and can even make things worse by clearing away competing bacteria.

Both have a cell wall, so are they similar? They both have a wall, yes, but built from different materials (peptidoglycan versus chitin). The shared idea is "a wall for shape and protection." The materials, and everything that follows from them, are different.

References

• Madigan MT, Bender KS, Buckley DH, Sattley WM, Stahl DA. Brock Biology of Microorganisms. 16th ed. Pearson; 2021.
• Carroll KC, Pfaller MA, et al. Manual of Clinical Microbiology. 12th ed. ASM Press; 2019.
• Tille PM. Bailey and Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2022.