Classification Of Bacteria On The Basis Of Nutrition 

• All living creatures need nutrition since these ingredients are employed in biosynthesis and energy generation.
• Like all living cells, bacteria need food and energy to create proteins, maintain structural membranes, and power biochemical reactions.
• Sources of carbon, nitrogen, phosphorus, iron and a vast number of other chemicals are needed for bacteria.
• Most of it is used in terms of carbon, nitrogen, and water.
• The carbon source and the energy source can be used to categorize the nutritional needs of bacteria.
• Some bacteria may produce energy using inorganic sources, whereas other bacteria must consume already-formed organic molecules.

Nutritional Types of Bacteria

Depending on their source of energy, organisms are classified as:

Phototrophs

• Phototrophs can use light as a source of energy. These microbes use light to produce energy.

Chemotrophs

• Chemical substances provide energy to these microorganisms. Such microorganisms are unable to perform photosynthesis.
• Depending on their electron supply, organisms are classified as:

Lithotrophs

• Lithotrophs utilize reduced organic molecules as electron donors.
• Both chemolithotrophs and photolithotrophs are possible.

Organotrophs

• Organotrophs can use organic substances as electron donors.
• Some of them could be photoorganotrophs or chemoorganotrophs.

Therefore a bacteria can be either:

Photo-lithotrops: These bacteria obtain their energy from light and obtain their electrons from reduced inorganic substances like H₂S. Such as Chromatium okeinii.

Photo-organotrophs: These bacteria use organic substances like succinate as a source of electrons and obtain their energy from light. Such as Rhodospirillum.

Chemo-lithotrophs: These bacteria use reduced inorganic substances like NH3 as a source of electrons to produce energy, such as Nitrosomonas.

Chemo-organotrophs: These bacteria use organic substances like glucose and amino acids as a source of electrons to produce energy. For instance, Pseudomonas pseudoflora

Like Pseudomonas pseudoflora, certain bacteria may exist as either chemo-lithotrophs or chemo-organotrophs because they can use either glucose or H₂S as an electron source.

On the basis of carbon source, bacteria may be:

• For usage in synthesizing cell components, carbon is necessary for all organisms in some form.
• Every living thing needs some CO₂, at least in modest amounts.
• But other species may use CO₂ as their main, or perhaps only, source of carbon; these are known as autotrophs (Autotrophic bacteria).
• Others, known as heterotrophs, use organic substances as their carbon source (Heterotrophic bacteria).

You may also like to read: Biochemical Test of Escherichia coli (E. coli)

Autotrophic Bacteria

These bacteria produce all of their own nourishment from inorganic materials (H₂O, CO₂, and H₂S salts).

There are two categories of autotrophic bacteria:

(I) Photoautotrophs

• These microorganisms absorb solar energy and convert it into chemical energy.
• CO2 is transformed into carbs throughout this process.
• Water serves as the hydrogen donor, and the reaction yields free oxygen.
• The primary purpose of photoautotrophs, such as cyanobacteria, which have chlorophyll pigment in their cells, is to collect sunlight.
• Some anaerobic photoautotrophic bacteria include the pigments bacteriovirdin and bacteriochlorophyll, respectively.

Purple Sulphur Bacteria

• These bacteria have the bacteriochlorophyll pigment, which is found on the thylakoids of the intracytoplasmic membrane. These bacteria use Chromatiiun and other sulfur compounds as fuel. Thiospirilium, Theopedia rosea.

Green Sulphur Bacteria

• Hydrogen sulfide (H2S) is used by these bacteria as a hydrogen donor. The reaction occurs when light and a pigment known as bacteriovirdin, bacteriopheophytin, or chlorobium chlorophyll, such as Chlorobium limicola, Chlorobacterium, etc., are present.
• These microorganisms get hydrogen via sulfides and thiosulfates, two inorganic sources. Consequently, these microorganisms are also referred to as photolithographs.

(II) Chemoautotrophs

• These bacteria can survive without light because they contain color and the dark phase of photosynthesis, which is what they lack in the light phase.
• These bacteria use oxygen from the atmosphere to oxidize certain inorganic materials.
• The energy (exothermic) released by this reaction is used to power the cell’s synthesis operations.

Sulphomonas (Sulphur Bacteria)

These bacteria, such as Thiobacillus and Beggiatoa, produce energy by the oxidation of elemental sulfur or H₂S.

Elemental Sulphur Oxidizing Bacteria: Thiobacillus denitrificans is a sulfur-denitrifying bacteria that convert elemental sulfur to sulfuric acid.

2S + 2H₂O + 3O₂ → 2H₂SO₄ + 126 kcal

Beggiatoa, a sulfide-oxidizing bacteria, oxidizes H₂S and emits sulfur.

2H₂S +4O₂ → 2H₂O + 2S + 141.8 cal

Hydromonas (Hydrogen Bacteria)

Some of these, such as Bacillus pantotrophus and Hydrogenomonas, transform hydrogen into water.

2H₂ + O₂ → 2H₂O + 55 kcal

4H₂ + CO₂ → 2H₂O + CH₄ + Energy

Ferromonas (Iron Bacteria)

These microorganisms live in water and produce their energy by oxidizing ferrous compounds into ferric forms—Leptothrix, for instance, or Thiobacillus ferroxidans.

4FeCo₃ + 6H₂O + O₂ → 4Fe (OH)₃ + 4CO₂ + 81 kcal

Methanomonas (Methane Bacteria)

• Methane is converted by these bacteria into water and carbon dioxide to provide energy.

Nitrosomonas (Nitrifying Bacteria)

• These bacteria produce nitrates by oxidizing ammonia and nitrogen molecules.
• Nitrosomonas oxidises NH₃ to nitrites.

NH₃ + ½O₂ ® H₂O + HNO₂ + Energy

• Nitrobacter converts nitrites to nitrates.

NO₂ + ½O₂ ® NO₂ + Energy

Carbon Bacteria

These bacteria, such as Oligotropha carboxydovorans and Bacillus oligocarbophillous, oxidize CO into CO₂.

2CO + O₂ → 2CO₂ + Energy

Heterotrophic Bacteria

• The organic materials, whether alive or dead, are where the heterotrophic bacteria get their ready-made meal.
• Heterotrophs make up the majority of harmful bacteria found in humans, other plants, and animals.
• While some heterotrops only need basic sustenance, others need vast amounts of vitamins and other substances that promote development. Fastidious heterotrophs are the names given to such creatures.
• Heterotrophic bacteria are of three types,

1. Photoheterotrophs

• Although these bacteria can use light energy, they are unable to utilize CO₂ as their exclusive carbon source.
• To meet their needs for carbon and electrons, they extract energy from organic substances. These bacteria contain a pigment known as bacteriochlorophyll.
• , Purple bacteria without sulfur (Rhodospirillum, Rhodomicrobium, Rhodopseudomonas palustris).

2. Chemoheterotrophs

Chemoheterotrophs rely on organic substances as both a source of carbon and energy. Such organic substances include proteins, lipids, and carbohydrates.

Glucose or Monosaccharide [(CH₂O)n] + O₂ → CO₂ + H₂O + Energy

Chemohetrotrophs may be divided into three primary groups based on how they receive organic nutrients:

I) Saprophytic Bacteria

• Saprophytic bacteria feed on dead organic waste that has begun to decompose, such as humus, leaves, fruits, vegetables, meat, and animal excrement.
• Enzymes are secreted by these microorganisms to break down and absorb the meal.
• Enzymes are released to convert complicated substances like protein and carbohydrates into more readily absorbed, simpler soluble substances.
• Examples include Acetobacter, Bacillus mycoides, and B. ramosus.

II) Parasitic Bacteria

• The tissues of the hosts that these bacteria are growing on provide them with food.
• They could be healthy, or they might spread dangerous infections.
• Pathogens include parasitic bacteria like Bacillus typhosus, B. anthracis, and B. tetani which cause various illnesses in plants and animals.
• Vibrio cholerae, Pseudomonas citri, B. cholerae, B. pneumoniae, B. diphtheriae, etc.

III) Symbiotic Bacteria

• Symbionts, or close companions of other species, are symbiotic microorganisms.
• They are advantageous to living things.
• Nitrogen-fixing bacteria, such as Rhizobium, Clostridium, Rhizobium spp., Bacillus radicicola, and B. azotobacter, are typical examples.
• These microorganisms are found in the roots of legume plants.
• These bacteria convert the free nitrogen in the atmosphere into nitrogenous chemicals that plants can use. In exchange, the bacteria receive nourishment and defense from the plant.

References

• Nutritional Classification of Bacteria
• Nutrition in Bacteria: Modes of Nutrition in Bacteria