Classification of Bacteria on the Basis of Nutrition with examples


An essential component of understanding the large diversity of microorganisms that live in our world is bacterial classification. By classifying bacteria according to their nutritional requirements, we learn a great deal about their metabolic capacities and ecological functions. This article attempts to investigate how bacteria are categorized based on nutrition, illuminating the numerous varieties and their importance in varied contexts.

Autotrophic Bacteria

A group of microorganisms known as autotrophic bacteria is capable of synthesizing their own organic compounds from inorganic materials. They differ from heterotrophic bacteria, which depend on external organic resources for nutrition, by this process, known as autotrophy. The distinctive feature of autotrophic bacteria is the use of inorganic carbon as the main source of carbon for growth.

Photosynthetic Autotrophic  Bacteria

Oxygenic Photosynthetic Bacteria

  • Cyanobacteria, a group of autotrophic microorganisms that produce oxygen through the process of photosynthesis. 
  • these bacteria use the light energy to transform carbon dioxide into organic chemicals.
  • Chlorophyll pigments are used in oxygenic photosynthesis to capture light energy and start the electron transport chain, which results in the generation of oxygen as a byproduct.
  • A variety of ecosystems, including freshwater, marine, and even symbiotic interactions with plants, are habitat to cyanobacteria.
  • Examples: Cyanobacteria, Prochlorococcus

Anoxygenic Photosynthetic Bacteria

  • The type of autotrophic microorganisms that can use light energy to synthesize organic molecules is called anoxygenic photosynthetic bacteria.
  • They do not produce oxygen as a byproduct, in contrast to oxygenic photosynthetic bacteria. The pigments bacteriochlorophylls, bacterioviridins, or bacteriorhodopsins are just a few of the pigments used by anoxygenic photosynthetic bacteria to absorb light energy and fuel their metabolic processes.
  • These bacteria may survive in a variety of environments, including the anaerobic habitats present in aquatic sediments, hot springs, and even animal digestive tracts.
  • Examples: Purple sulfur bacteria, Green non-sulfur bacteria

Chemolithotrophic Autotrophic Bacteria

A group of microorganisms known as chemolithotrophic autotrophic bacteria or chemolithoautotrophic bacteria obtains their energy from the oxidation of inorganic substances. Instead of using light or organic molecules as an energy source, these bacteria use a variety of inorganic substrates. They can survive and even thrive in conditions without organic matter, like sulfur-rich hot springs or deep-sea hydrothermal vents.

Sulfur-Oxidizing Bacteria

  • Sulfur-oxidizing bacteria are chemolithotrophic autotrophs that oxidize inorganic sulfur compounds such as thiosulfate (S2O3-), elemental sulfur (S0), and hydrogen sulfide (H2S).
  • They carry out these oxidation reactions using specialized enzymes like sulfur oxygenases or thiosulfate reductases.
  • Sulfur-oxidizing bacteria contribute to the transformation of sulfide minerals into sulfate and are essential for sulfur cycling in both marine and terrestrial environments. They play a vital part in biogeochemical cycles.
  • Examples: Thiobacillus, Beggiatoa

Iron Oxidizing Bacteria

  • Iron-oxidizing bacteria are chemolithotrophic autotrophs that get their energy from oxidizing ferrous iron (Fe2+).
  • These bacteria have special enzymes called rusticyanins or proteins that resemble rusticyanins, which promote the oxidation of iron.
  • Acidic mine drainage and iron-rich soils are two examples of habitats where iron-oxidizing bacteria are frequently found.
  • They have an impact on the creation of iron-rich deposits and are crucial to the iron cycle.
  • Examples: Gallionella, Leptothrix

Nitrogen fixing Bacteria

  • Nitrogen-fixing bacteria are chemolithotrophic autotrophs with the ability to fix nitrogen in the atmosphere (N2) to produce ammonia (NH3).
  • This process is critical to the nitrogen cycle because it allows nitrogen to be incorporated into organic molecules.
  • In symbiotic partnerships with plants like legumes, nitrogen-fixing bacteria live inside specialized structures called nodules and supply the plant with an essential source of nitrogen for growth.
  • Examples: Rhizobium, Azotobacter

Heterotrophic bacteria

Heterotrophic bacteria are a wide group of microorganisms that get their carbon and energy from organic sources. They cannot create their own organic compounds, unlike autotrophic bacteria, so they must obtain nutrients from external organic materials. They then break these complex organic molecules down into simpler compounds to produce energy and create cellular components.

Aerobic heterotrophic bacteria

Saprophytic Bacteria

  • Aerobic heterotrophic bacteria that specialize in digesting decaying organic substances are called saprophytic bacteria.
  • They are essential for recycling of organic materials and the cycling of nutrients in ecosystems.
  • Extracellular enzymes secreted by saprophytic bacteria help break down complex organic materials into simpler molecules that may be easily absorbed and used by the bacterium for growth and energy production.
  • These bacteria are prevalent in soil, water, and other organic debris-rich habitats.
  • Examples:  E. coli, Spirochaeta

Parasitic bacteria

  • Parasitic bacteria are heterotrophic microorganisms that rely on living hosts for their nutritional requirements.
  • They take nutrition from their host’s tissues or fluids by infecting other species such as plants, animals, or even other bacteria as hosts. Invading host cells, resisting host immune defenses, and obtaining nutrition for their own survival and reproduction are all strategies used by parasitic bacteria.
  • The pathogens that cause illnesses including cholera, Lyme disease, and tuberculosis are examples of parasitic bacteria.
  • Examples are Mycobacterium tuberculosis, Salmonella enterica

Anaerobic Heterotrophic Bacteria

Fermentative Bacteria

  • A group of anaerobic heterotrophs known as fermentative bacteria use fermentation, a metabolic activity that enables them to produce energy in the absence of oxygen.
  • These bacteria use organic substances as electron acceptors and donors to create molecules high in energy, such as adenosine triphosphate (ATP).
  • Depending on the particular fermentative pathway used by the bacteria during fermentation, different end products, such as organic acids, alcohols, or gases, are frequently produced during the process.
  • The gastrointestinal tracts of animals and the sediments of environments devoid of oxygen are only two examples of the many anaerobic habitats where fermentative bacteria can be found.
  • Examples: Clostridium, Lactobacillus

Sulfate-Reducing Bacteria

  • Anaerobic heterotrophic sulfate-reducing bacteria use sulfate (SO4-) as an electron acceptor during respiration.
  • Because they transform sulfate into sulfide (S2), which can be used by other sulfur-oxidizing bacteria, these bacteria are essential to the sulfur cycle.
  • Sulfate-reducing bacteria are frequently discovered in low oxygen environments, such as marine sediments, anaerobic sludge, or hydrothermal vents.
  • Some sulfate-reducing microorganisms are also pathogenic, meaning they can harm both people and animals.
  • Examples: Desulfovibrio, Desulfotomaculum

Mixotrophic bacteria

Autotrophic and heterotrophic type of metabolism are combined in a unique nutritional approach used by mixotrophic bacteria. These adaptable microbes can use both inorganic and organic carbon sources to meet their growth and energy requirements. Mixotrophic bacteria can adapt to changing environmental conditions and increase their chances of survival by switching between various nutritional modes.

Types of Mixotrophic Bacteria

Photoheterotrophic bacteria

  • Mixotrophic bacteria that can use light as an energy source but rely on organic carbon compounds as their main carbon source are known as photoheterotrophic bacteria.
  • Similar to photosynthetic autotrophic bacteria, these bacteria use phototrophic pigments to gather light energy, but they also rely on organic molecules to obtain carbon and nutrients.
  • Aquatic ecosystems are one setting where photoheterotrophic bacteria are common and where they contribute significantly to the carbon cycle.
  • Examples: Rhodobacter, Rhodospirillum

Chemoheterotrophic Bacteria

  • Chemoheterotrophic bacteria are mixotrophs that use organic carbon sources for growth and metabolism and obtain energy from the oxidation of organic molecules like sugars or organic acids.
  • Due to their numerous metabolic pathways, these bacteria can convert complex organic molecules into simpler ones that can be used for energy production.
  • Numerous ecosystems, including soil, water, and the microbiomes of plants and animals, are rich in chemoheterotrophic bacteria.
  • Examples: Escherichia coli, Pseudomonas aeruginosa

Oligotrophic bacteria

Oligotrophic bacteria have developed particular characteristics to survive in conditions with less nutrients. They have mechanisms to scavenge and preserve vital nutrients, making them extremely effective at utilizing nutrients. In comparison to copiotrophic bacteria, oligotrophic bacteria frequently have smaller cell sizes, more streamlined genomes, and slower metabolic rates, which allow them to use scarce resources effectively.

Adaptations of Oligotrophic Bacteria to Low-Nutrient Environments

Oligotrophic bacteria use a variety of adaptations to survive in environments with few nutrients. These include the creation of specialized transport systems to gather limited nutrients, the synthesis of extracellular enzymes to effectively breakdown organic materials, and the construction of biofilms to improve nutrient uptake. To survive extended periods of food deprivation, oligotrophic bacteria can also create dormant forms, such as endospores.

Examples: Pelagibacter ubique, Prochlorococcus

Copiotrophic Bacteria,

Microorganisms known as copiotrophic bacteria grow in nutrient-rich habitats that are distinguished by a surplus of organic carbon and other nutrients. Compared to oligotrophic bacteria, they frequently have bigger cell sizes, better biomass yields, and more varied metabolic capabilities. Copiotrophic bacteria are frequently found in a variety of habitats, including rich soils, wastewater treatment facilities, and locations exposed to organic pollutants.

Adaptations of Copiotrophic Bacteria to High-Nutrient Environments

Copiotrophic bacteria have developed a variety of modifications to take advantage of situations rich in nutrients. They have developed regulatory mechanisms to quickly adapt to variations in nutrition availability, and they contain a variety of extracellular enzymes to effectively break down complicated chemical compounds. Copiotrophic bacteria perform crucial roles in the breakdown of organic matter and the cycling of nutrients. They have the ability to quickly colonize and dominate nutrient-rich settings.

Examples: Escherichia coli, Bacillus subtilis

Fastidious Bacteria

A group of microorganisms known as fastidious bacteria has extremely specific and demanding nutritional requirements. Fastidious bacteria have specialized nutritional requirements and frequently need sophisticated and enriched culture conditions in order to develop, unlike other bacteria that can grow on a variety of media. They are often fastidious in terms of pH, temperature, and oxygen conditions as well. Due to their unique niches or symbiotic relationships with other organisms, some bacteria may have evolved this dependency on particular nutrients.

Examples: Haemophilus influenzae (requires hemin and NAD), Neisseria gonorrhoeae (requires specific growth factors)

Symbiotic Microorganisms

Symbiotic bacteria interact in ways that can be advantageous or harmful for both organisms These other species can be other bacteria, plants, animals, or even other symbiotic bacteria. They frequently stay in certain host tissues or organs where they perform essential functions or take advantage of resources to ensure their own survival and reproduction. Symbiotic bacteria have developed ways to connect and communicate with their hosts, enabling them to form and sustain these relationships.

Mutualistic Symbiotic Bacteria

Plants with rhizobia and legumes

Rhizobia are bacteria that produce nodules on the roots of legume plants and are mutualistic. Rhizobia in these nodules use nitrogen fixation to turn ambient nitrogen into ammonia, which the plants need as a source of nitrogen. Rhizobia receives nutrients and carbohydrates from the plants in exchange. Rhizobia may access a carbon supply that is rich in energy due to this mutualistic interaction, which also improves the growth and nitrogen nutrition of leguminous plants.

Examples: Rhizobium leguminosarum, Bradyrhizobium japonicum

Gut Microbiota and Humans

A diverse community of mutualistic bacteria that are present in the human gut are essential to the health of the host. These microorganisms help the body digest food, produce vitamins, metabolize bile acids, and control immunological function. Together, the gut microbiota and people have evolved over time, with the bacteria taking advantage of the gut’s nutrient-rich environment while the host received numerous advantages.

Examples: Bacteroides fragilis, Escherichia coli

Pathogenic Symbiotic Bacteria

Intracellular Pathogens

Some symbiotic bacteria can create intracellular infections in host cells, which can result in harmful effects. To enter host cells, avoid immune reactions, and take advantage of host resources, these bacteria have evolved sophisticated systems. Bacteria like Salmonella are examples of intracellular pathogens since they may enter host cells and multiply there, resulting in illnesses like typhoid fever.

Examples: Mycobacterium tuberculosis, Salmonella enterica

Extracellular Pathogens

extracellular symbiotic bacteria can cause disease By colonization and multiplying in host tissues or bodily fluids.  They develop virulence factors that give them the ability to get across the host’s defenses and damage the tissues of the host. Bacteria like Streptococcus pneumoniae, which may cause pneumonia and other illnesses, are an example of an extracellular pathogen.

Examples: Streptococcus pneumoniae, Staphylococcus aureus

Commensal Bacteria

Bacteria known as commensal bacteria survive with other organisms without causing harm or giving obvious advantages. These microorganisms live inside their hosts in a variety of ecological niches, frequently colonizing bodily surfaces including the skin, mouth cavity, or gastrointestinal system.

Examples: Staphylococcus epidermidis, Bifidobacterium spp.

Amensalistic Bacteria

Amensalistic bacteria interact in a way that causes one organism to suffer while leaving the other unharmed. In these interactions, one organism releases substances or elements that prevent or reduce the development or survival of another organism.

Antibiotics or toxins that amensalistic bacteria secrete prevent the growth or survival of other species without providing any direct benefit to themselves. These interactions are frequently competitive in nature, giving the bacteria an advantage over their competitors by lowering the fitness or viability of nearby organisms.

Examples of Amensalistic Interactions between Bacteria and Other Organisms

There are many environments where bacteria and other species interact amensally. For example, several soil bacteria create antibiotics that prevent the expansion of neighboring microbes, reducing competition for resources. Similar to bacteriocins, which are antimicrobial peptides that inhibit the growth of potential pathogens and provide a protective impact on the host, some bacteria in the human microbiota also generate them.

Examples: Streptomyces spp., Penicillium spp.


In conclusion, bacterial nutrition is a complex and diverse field that encompasses a wide array of metabolic strategies and ecological interactions. Autotrophic bacteria harness energy from inorganic sources, while heterotrophic bacteria rely on organic compounds. Mixotrophic bacteria combine both autotrophic and heterotrophic modes of nutrition


  • Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: An introduction. Pearson Education Limited.
    Willey, J. M., Sandman, K. M., Wood, D. H., & Prescott, L. M. (2019). Prescott’s microbiology (11th ed.). McGraw Hill.
  • Greemwood, R. S. (2002). Medical Microbiology. London: Churchill Livingstone.
  • J.Pelezar. (1993). Microbiology. Tata McGraw hill.
Mubashir Iqbal
Mubashir Iqbal

Mubashir Iqbal is a highly dedicated and motivated Microbiologist with an MPhil in Microbiology from the University of Veterinary and Animal Sciences. Currently, he is researching the efficacy of commercially available SARS Cov-2 vaccines to neutralize the omicron variant in Pakistan. He holds a Bachelor's degree in Microbiology and has experience in chemical and microbiological analysis of water samples, managing SOPs and documents according to standard ISO 17025. Additionally, he has worked as an internee in BSL 3, Institute of Microbiology, UVAS, where he gained experience in RNA extraction, sample processing, and microscopy.

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