Bacteria: Nutrition and its Types, Autotrophic Nutrition and Heterotrophic Nutrition
The mode of Nutrition in bacteria can be categorized into two types
1. Autotrophic Nutrition
2. Heterotrophic Nutrition
- The bacteria which are capable of synthesizing their food by themselves from organic and inorganic substances are called Autotrophic Nutrition in bacteria. Based on the requirement of energy the Autotrophic bacteria are classified as follows
- Phototrophs: the bacteria which use light energy as a source of energy are known as photo-Autotrophs. It is of two types
1. Green sulphur bacteria
2. Purple Sulphur bacteria
1. Green sulphur bacteria: these are small nonmotile, rod-shaped bacteria that are anaerobic photoautotrophs. they contain a pigment called Chlorobium chlorophyll also known as Bacterioviridin that is responsible for absorbing light energy. these bacteria use H2S or other reduced inorganic sulphur compounds as electron donors.e,g Chlorobium, etc
2. Purple Sulphur bacteria: These are also autotrophs and their photosynthetic pigments are bacteriochlorophyll a or b. e,g Thiospirillum, and Amoebobacter.
3. Non-Sulphur purple bacteria: These are motile bacteria that don’t produce gas vacuoles and never accumulate sulphur within the cell. their photosynthetic pigment is also bacteriochlorophyll.
B. Chemotrophs: the bacteria which obtain energy from chemical compounds are known as chemoautotrophs. They derive their energy from ammonia, nitrate, nitrite, ferrous iron, hydrogen sulphide and other inorganic compounds for the synthesis of their food. These are of following types
1. Sulphur bacteria: these bacteria are found in sulphur-containing terrestrial and aquatic environments. E,g Beggiatoa, Thiobacillus
2. Iron Bacteria: These bacteria form natural colonies in freshwater ponds and springs with high contents of reduced sulphur salts e,g Ferrobacillus, Gallionella.
3. Hydrogen Bacteria: Many species of chemoautotrophic bacteria can grow with molecular hydrogen. E,g P. facilis
4. Nitrifying bacteria: These are soil-borne obligate autotrophs incapable of growing in the absence of a specific inorganic energy source. e,g Nitrobacter.
Organisms are classified as follows based on their electron source:
1. Lithotrophs: Lithotrophs are creatures that may employ reduced organic molecules as electron suppliers.
2. Organotrophs: Organotrophs are creatures that can utilise organic substances as electron suppliers.
3. Photo-lithotrops: These bacteria get their energy from light and get their electrons from reduced inorganic compounds like H2S. E,g Chromatium okeinii
4. Photo-organotrophs: These bacteria get their energy from light and get their electrons from organic substances like succinate.e,g Rhodospirillum,
5. Chemo-lithotrophs: These bacteria get their energy from inorganic molecules that have been reduced, such as NH3.
6. Chemo-organotrophs: These bacteria use organic substances like glucose and amino acids as a source of electrons to generate energy. E,g Pseudomonas pseudoflora,
7. Carbon Bacteria:
These bacteria oxidize CO into CO2 e.g., B. oligocarbophillous,
Heterotrophic bacteria get their ready-made nourishment from living or dead organic matter. Heterotrophic bacteria make up the majority of harmful bacteria found in humans, other plants, and animals.
Heterotrophic bacteria are of various types such as
A. Photoheterotrophs: these are those bacteria that can use light energy, they are can not utilize CO2 as their main carbon source.
To meet their carbon and electron requirements, they obtain energy from organic substances. These bacteria contain the pigment bacteriochlorophyll. Purple non-sulphur bacteria (Rhodospirillum,)
Organic molecules such as carbohydrates, lipids, and proteins provide both carbon and energy to chemoheterotrophs.
(ii) Parasitic bacteria.
(iii) Symbiotic bacteria
(i)Saprophytic bacteria. Saprophytic bacteria feed on dead and organic decaying stuff such as leaves, fruits, vegetables, meat, animal faeces, leather, and hummus, among other things. e,g Bacillus mycoides, Bacillus ramosus, Acetobacter,
(ii) Parasitic bacteria: These bacteria get their nutrients from the tissues of the hosts they live in. e,g Bacillus typhosus, Bacillus anthracis, Bacillus tetani etc.
(iii) Symbiotic bacteria: Symbiotic bacteria are those organisms that live in symbiotic association with other organisms. They are useful to organisms.e,g Nitrogen-fixing bacteria such as Bacillus radicicola, Bacillus azotobacter, Rhizobium, Clostridium, Rhizobium spp.,