What is the difference between a bacterium and a fungus?

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The other day, our microbiology professor asked us to compare bacteria and fungi, and it got me thinking about how often we confuse the two. I remembered reading in Brock’s textbook how different their cell structures, reproduction, and even roles in nature are. This breakdown really helped me understand their unique features clearly—especially why antibiotics don’t work on fungi.

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Markko 2025-06-11T07:49:05+00:00 1 Answer 3 views
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  1. fleming
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    2025-06-11T07:51:32+00:00
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    Cellular Structure

    • Bacteria: Prokaryotic organisms with relatively simple cellular organization. They lack membrane-bound organelles, including a nucleus. Bacterial cells are typically small (0.5–5 μm) and may be spherical (cocci), rod-shaped (bacilli), or spiral (spirilla/spirochetes).
    • Fungi: Eukaryotic organisms with complex cellular organization. They have membrane-bound organelles, including a true nucleus. Fungal cells are generally larger (3–50+ μm) and may exist as single cells (yeasts) or form multicellular filamentous structures called hyphae, which collectively form a mycelium.

    Cell Wall Composition

    • Bacteria: Most have cell walls containing peptidoglycan. Gram-positive bacteria have thick peptidoglycan layers, while Gram-negative bacteria have thinner peptidoglycan layers and an outer membrane with lipopolysaccharides.
    • Fungi: Cell walls primarily contain chitin, glucans, and mannoproteins. They lack peptidoglycan, which is why antibiotics like penicillin (targeting peptidoglycan) are ineffective against them.

    Genetic Material

    • Bacteria: Have a single, circular chromosome located in the cytoplasm, along with plasmids. Genome size ranges from about 0.5 to 9 million base pairs.
    • Fungi: Have multiple linear chromosomes within a nucleus. Their genomes are generally larger (8–100+ million base pairs) and also include organellar DNA in mitochondria.

    Reproduction

    • Bacteria: Reproduce asexually via binary fission. Genetic exchange occurs through conjugation, transformation, or transduction—not true sexual reproduction.
    • Fungi: Reproduce both asexually and sexually:
      • Asexual: Budding (yeasts), fragmentation, or spore production.
      • Sexual: Fusion of mating types/gametes followed by meiosis.

    Metabolism and Nutrition

    • Bacteria: Highly diverse. They can be:
      • Autotrophs (photoautotrophs or chemoautotrophs)
      • Heterotrophs (organic compound consumers)
      • Nitrogen fixers
      • Facultative in switching metabolic modes
    • Fungi: Exclusively heterotrophic. They acquire nutrients through:
      • Saprotrophy (decomposing matter)
      • Parasitism (host-derived nutrients)
      • Mutualism (e.g., mycorrhizae, lichens)

      Fungi secrete digestive enzymes externally and absorb nutrients (absorptive nutrition).

    Motility

    • Bacteria: Many are motile using flagella or gliding.
    • Fungi: Generally non-motile. Some spores may be motile (zoospores), but mature fungi do not move.

    Ecological Roles

    • Bacteria: Function as decomposers, nitrogen fixers, and key players in biogeochemical cycles. Include beneficial microbes and pathogens.
    • Fungi: Primary decomposers of lignin and cellulose. Form symbiotic relationships (e.g., mycorrhizae, lichens). Also include beneficial and pathogenic species.

    Medical Significance

    • Bacterial Infections: Usually acute and treatable with antibiotics. Examples: strep throat, TB, pneumonia, food poisoning.
    • Fungal Infections: Often chronic and treated with antifungals. Common in immunocompromised individuals. Examples: athlete’s foot, ringworm, candidiasis, aspergillosis.

    Size and Complexity

    • Bacteria: Microscopic, 0.5–5 μm diameter single cells.
    • Fungi: Range from microscopic yeasts (3–5 μm) to large multicellular organisms. The largest known is a honey fungus (Armillaria ostoyae) covering over 2,385 acres.

    Examples

    • Bacteria: Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Bacillus subtilis, Pseudomonas aeruginosa
    • Fungi: Saccharomyces cerevisiae (yeast), Agaricus bisporus (mushroom), Penicillium (penicillin source), Candida albicans, Aspergillus spp.

    In summary: Bacteria and fungi differ in their cellular structures, reproduction, metabolism, ecological functions, and medical impacts. Understanding these differences is vital across medicine, agriculture, and environmental science.

    Source: Madigan, M.T., et al. Brock Biology of Microorganisms; Deacon, J. Fungal Biology.

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