NUTRITIONAL REQUIREMENTS OF MICRO-ORGANISMS (BACTERIA)

CLASSIFICATION OF BACTERIA ON THE BASIS OF NUTRITION.

NUTRITIONAL REQUIREMENTS OF BACTERIA

Nutrients are substances used in biosynthesis and energy production & release there for they are required for all living things and also for microbial growth.

Bacteria require adequate nutrition, energy, optimum pH, temperature and oxygen for growth and multiplication. Bacteria require sources of carbon, nitrogen, phosphorous, iron and a large number of other molecules.

The rate at which bacteria grow and divide depends on the nutritional status of the environment.

E.g. The growth of single E.coli cell into new daughter cell may occour within 20-30 minutes in rich laboratory media. Whereas the same process is much slower in a nutritionally depleted media.

Bacteria can be classified depending on nutritional requirements are as follows

1. Source of energy

2. Source of electron

3. Source of carbon

SOURCE OF ENERGY:- On the basis of energy source bacteria are divided in to two categories…

Phototrophs: - Bacteria which obtain energy from sunlight are called phototrophs.

E.g. Rhodospirillum rubrum.

Chemotrophs: - Bacteria which obtain energy from chemical copmpounds are called phototrophs. E.g. E.coli.

SOURCE OF ELECTRON: - All microorganisms require a source of electron for their metabolism. On the basis of electron source bactreia are divided in to two categories…

Lithotrophs:- Bacteria which use reduced inorganic compounds as electron donor are called lithotrophs. E.g. Pseudomonas pseudoflava.

Organotrophs:- Bacteria which use organic compounds as electron donor are called organotrophs. E.g. E.coli.

Among the phototrophic bacteria….

Photolithotrophs:- Some bacterial species gain energy from light and used inorganic compounds (H2S) as source of electron they are called as photolithotrophs. E.g. Chromatium okenii.

Photoorganotrophs:- Some other bacterial species gain energy from light and used organic compounds such as fatty acids & alcohols as source of electron they are called as photoorganotrophs. E.g. Rhodospirillum rubrum.

Among the chemotrophic bacteria….

Chemolithotrophs:- Some bacterial species use inorganic compounds as a source of electron and are called as chemolithotrophs. E.g. Nitrosomonas europaea.

Chemoorganotrophs:- Some other bacterial species use organic compounds such as sugar & amino acids as a source of electron and are called as chemoorganotrophs. E.g. Pseudomonas pseudoflora.

SORCE OF CARBON:- All microorganism require carbon for synthesizing cell components, On the basis of carbon source bacteria may be:

Autotrophs:- Some specie use Co2 as the major source of carbon and they are called as autotrophs (Autotrophic bacteria). E.g. Chromatium okenii.

Heterotrophs:- Other species require organic compounds as a source of carbon, such species are called as heterotrophs (Heterotrophic bacteria). E.g. E.coli.

Autotrophic bacteria:- The autotrophic bacteria are of two types…

I. Photoautotroph’s

II. Chemoautotroph’s

Photoautotrophs:- They capture the energy of sunlight and convert it into the chemical energy.

In this process, CO2 is reduced to carbohydrates.

Purple Sulphur Bacteria:- These bacteria obtain energy from sulfur compounds e.g., Chromatiiun. Theopedia rosea.

Green Sulphur Bacteria: These bacteria use hydrogen sulfide (H2S) as hydrogen donor. The reaction takes place in the presence of light and pigment termed as bacteriovirdin. e.g., Chlorobium limicola, Chlorobacterium.

Chemoautotrophs:- These bacteria oxidize certain inorganic substances with the help of atmospheric oxygen. This reaction releases the energy (exothermic) which is used to drive the synthetic processes of the cell.

They do not require light (lack the light phase but have the dark phase of photosynthesis) and pigment for their nutrition.

Sulphomonas (Sulphur bacteria): These bacteria obtain energy by oxidation of elemental sulphur or H2S, E.g., Thiobacillus, Beggiatoa.

Ferromonas (Iron bacteria): These bacteria inhabit water and obtain energy by oxidation of ferrous compounds into ferric forms. e.g., Thiobacillus ferroxidans, Ferro bacillus,

Methanomonas (Methane bacteria): These bacteria get their energy by oxidation of methane into water and carbon dioxide.

Nitrosomonas (Nitrifying bacteria): These bacteria get their energy by oxidation of ammonia and nitrogen compounds into nitrates.

Carbon Bacteria: These bacteria oxidizes CO into CO2 e.g., Bacillus oligocarbophillous, Oligotropha carboxydovorans

Heterotrophic bacteria:- The heterotrophic bacteria obtain their food from organic substances either living or dead. Heterotrophic bacteria are of two types:

Photoheterotrophs:- These types of bacteria obtain energy from organic compounds to fulfill the requirements of carbon and electron. They can utilize light energy but cannot use CO2 as their sole source of carbon. E.g. Purple non-sulphur bacteria (Rhodospirillum, Rhodomicrobium)

Chemoheterotrophs:- Chemoheterotrophs obtain both carbon and energy from organic compounds such as carbohydrates, lipids and proteins.

Sources of nitrogen:- Bacteria can use nitrogen from the atmosphere or from inorganic compounds such as nitrites, nitrates, ammonium salt or organic compounds such as amino acids. Nitrogen is a major component of proteins and nucleic acids.

Source of sulphur:- many bacterial species obtain sulphur from organic sulphur compounds, inorganic sulphur compounds and elemental sulphur. Sulphur is necessary for synthesis of amino acids.

Mineral salts:- The cations such as sodium, magnesium, potassium, calcium & iron and the anions such as sulphate & phosphate these are the important mineral salts that is necessary for bacterial growth. These are normally present in the natural environment or may be added in culture media.

Growth factors and bacterial vitamins:- Some species of bacteria require organic compounds in minute quantities for growth. Some bacteria are capable of synthesizing their entire requirements of vitamins from culture media. Some other species cannot synthesize from media and do grow properly in absence of vitamins. Hence for the growth of these species specific vitamins are added in culture media.

No	Species	Required vitamins for growth
01	Staphylococcus aureus	Thiamine, Nicotinic acid
02	Bacillus anthracis	Thiamine (vitamin B1)
03	Lactobacillus	Pyridoxine (Vitamin B6), Cobalamine (vitamin B12)
04	Clostridium tetani	Riboflavin (vitamin B2)
05	Haemophilus influenzae	Hematin

Water:- Water is the major essential nutrient as it accounts for about 80 to 90% of the total weight of the cells. Water is a highly polar compound and it contains micro-nutrients and trace elements which are required for bacterial growth.