What is the difference between a bacterium and a cyanobacterium?

Question

I remember reading about cyanobacteria while prepping for a lab quiz, and I got a bit confused because they were called bacteria but also seemed plant-like. Turns out, cyanobacteria are actually a special group of bacteria that can photosynthesize like plants. This answer breaks it all down clearly—same family, but some serious differences. Great for clearing up the mix-up.

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Alicia 2025-06-13T13:52:13+00:00 1 Answer 2 views
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  1. fleming
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    2025-06-13T13:55:10+00:00
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    Relationship

    Cyanobacteria as a Subset of Bacteria: Cyanobacteria (formerly called “blue-green algae”) constitute a phylum (Cyanobacteria) within the domain Bacteria. They are true prokaryotes, lacking membrane-bound organelles and a nucleus.

    Key Similarities (Features Shared with Other Bacteria)

    1. Prokaryotic Cell Structure: Like all bacteria, cyanobacteria lack membrane-bound organelles and a true nucleus. Their genetic material is located in the nucleoid region of the cell.
    2. Cell Size: Typically microscopic, with dimensions similar to other bacteria (generally 1–10 μm).
    3. Cell Wall Structure: Possess a peptidoglycan cell wall, characteristic of bacteria. They are generally considered Gram-negative in cell wall structure, having an outer membrane beyond the peptidoglycan layer.
    4. Reproduction: Reproduce asexually through binary fission or multiple fission.
    5. Ribosomes: Contain 70S ribosomes, typical of prokaryotes.

    Key Differences (Features Distinguishing Cyanobacteria from Most Other Bacteria)

    1. Photosynthesis:
      • Cyanobacteria: Perform oxygenic photosynthesis, similar to plants and algae. They contain chlorophyll a and use water as an electron donor, producing oxygen as a byproduct.
      • Most Other Bacteria: Are not photosynthetic, or if they are (like purple and green bacteria), they perform anoxygenic photosynthesis using different pigments and electron donors, not producing oxygen.
    2. Photosynthetic Apparatus:
      • Cyanobacteria: Contain thylakoid membranes where photosynthetic pigments are arranged, similar to chloroplasts in plants and algae. These are internal membrane systems distinct from the plasma membrane.
      • Most Other Bacteria: Photosynthetic bacteria typically have their photosynthetic apparatus in the plasma membrane or in invaginations of it, not in specialized thylakoids.
    3. Pigments:
      • Cyanobacteria: Contain chlorophyll a (like plants) and phycobilins (phycocyanin, allophycocyanin, and sometimes phycoerythrin), which give many species their characteristic blue-green or sometimes red color.
      • Most Other Bacteria: Photosynthetic bacteria contain bacteriochlorophylls and carotenoids, but not chlorophyll a or phycobilins.
    4. Carbon Fixation:
      • Cyanobacteria: Use the Calvin cycle for carbon fixation, similar to plants.
      • Most Other Bacteria: May use various carbon fixation pathways, including the Calvin cycle, reverse TCA cycle, or other alternatives.
    5. Cellular Differentiation:
      • Cyanobacteria: Some filamentous species can differentiate specialized cells:
        • Heterocysts: Thick-walled cells specialized for nitrogen fixation
        • Akinetes: Resistant resting cells that can survive adverse conditions
        • Hormogonia: Motile filaments involved in dispersal
      • Most Other Bacteria: Generally show less complex cellular differentiation, though some groups (like Streptomyces) do form specialized structures.
    6. Ecological Role:
      • Cyanobacteria: Primary producers in many ecosystems, contributing significantly to global oxygen production and carbon fixation. Some are important nitrogen fixers.
      • Most Other Bacteria: Fill diverse ecological roles as decomposers, pathogens, symbionts, etc., but rarely serve as primary producers.
    7. Evolutionary Significance:
      • Cyanobacteria: Ancestors of cyanobacteria gave rise to chloroplasts in plants and algae through endosymbiosis. They were responsible for oxygenating Earth’s atmosphere during the Great Oxygenation Event approximately 2.4–2.0 billion years ago.
      • Most Other Bacteria: Have different evolutionary histories and impacts.
    8. Habitat:
      • Cyanobacteria: Predominantly aquatic (freshwater and marine) or found in moist terrestrial environments. Some can survive in extreme environments like hot springs or desert crusts.
      • Most Other Bacteria: Found in virtually all habitats on Earth, with various adaptations to specific environments.

    Examples

    • Cyanobacteria: Nostoc, Spirulina/Arthrospira, Microcystis, Prochlorococcus, Synechococcus
    • Other Bacteria: Escherichia coli, Bacillus subtilis, Streptococcus pneumoniae, Pseudomonas aeruginosa, Clostridium botulinum

    Practical Significance

    1. Environmental Impact:
      • Cyanobacteria can form harmful algal blooms in nutrient-rich waters, producing toxins (cyanotoxins) that affect humans, wildlife, and ecosystems.
      • Some cyanobacteria fix atmospheric nitrogen, contributing to soil fertility and supporting plant growth.
    2. Biotechnology:
      • Certain cyanobacteria (like Spirulina) are cultivated as nutritional supplements or potential biofuel sources.
      • Cyanobacterial pigments have applications in food coloring and fluorescent markers.
    3. Research:
      • Cyanobacteria serve as model organisms for studying photosynthesis, nitrogen fixation, and the evolution of chloroplasts.

    While cyanobacteria are true bacteria (prokaryotes), they possess unique characteristics that distinguish them from most other bacterial groups, particularly their ability to perform oxygenic photosynthesis using chlorophyll a and phycobilins in specialized thylakoid membranes. These features reflect their distinct evolutionary history and ecological roles, including their crucial contribution to Earth’s oxygenation and their ancestral relationship to chloroplasts in plants and algae.

    Source:
    Whitton, B.A., & Potts, M. (Eds.). The Ecology of Cyanobacteria: Their Diversity in Time and Space
    Madigan, M.T., et al. Brock Biology of Microorganisms

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