For growth and multiplication, bacteria need adequate nutrition, optimum pH, temperature and oxygen. Microorganisms have been cultivated in laboratories using appropriate artificial media that contain sources of carbon, nitrogen, hydrogen, oxygen, phosphorous, and other elements in very small quantities, such as sodium, potassium, magnesium, and iron. Bacteria can be classified depending on nutritional requirements such as source of energy, electron, carbon, nitrogen etc.
Nutritional requirements of bacteria
Phototrophs are bacteria that get their energy from sunlight (example- Rhodospirillum rubrum), while chemotrophs get their energy from chemical reactions (example- Escherichia coli).
For their metabolism, all microbes need an electron source. Lithotrophic bacteria (example- Pseudomonas pseudoflava) are those that use reduced inorganic compounds as electron donors, whereas organotrophic bacteria (example- Escherichia coli) are those that use organic compounds as electron donors.
Among the phototrophic bacteria, some species use inorganic compounds (H2S) as source of electrons and are called as photolithotrophs (example- Chromatium okenii) and those which use organic compounds such as fatty acids and alcohols as electron donors are called photo organotrophs (example- Rhodospirillum rubrum).
Within the chemotrophic bacterial community, certain species are referred to as chemolithotrophs (example- Nitrosomonas europaea) because they obtain their electrons from inorganic compounds, while other species, known as chemoorganotrophs (example- Escherichia coli), obtain their electrons from organic compounds like sugar and amino acids.
Microorganisms requires carbon for synthesizing cell components. However, some species use CO2 as the major source of carbon. These microorganisms are called autotrophs (example- Chromatium okenii). Apart from these which requires organic compounds as a source of carbon are called as heterotrophs (example- Echerichia coli)
Nitrogen is a major component of protein and nucleic acids. Bacteria can use nitrogen from the atmosphere, inorganic compounds like nitrites and nitrates, ammonium salts, and organic compounds like amino acids.
Many bacterial species utilize sulphur from organic sulphur compounds, inorganic sulphur compounds, and elemental sulphur. Sulphur is required for the synthesis of amino acids. For example- cysteine and methionine etc.
Phosphorous is supplied in the form of phosphate and is an essential component of nucleotides, nucleic acids, phospholipids etc.
Mineral salts are normally present in the natural environment or may be added in the culture media. Bacteria needs salts, particularly the anions such as phosphates and sulphates and the cations as sodium, potassium, magnesium, iron and calcium.
Growth factor or Bacterial Vitamins
Some bacterial species require minute amounts of organic compounds to grow. These are referred to as growth factors or bacterial vitamins. Some bacteria can synthesize all of the vitamins they require from the culture medium. Some other species are unable to synthesize vitamins from the culture medium and therefore do not grow in their absence. As a result, vitamins are added to the culture media to allow these species to grow.
Water is a major and essential nutrient as it comprises for about 80 to 90 percent of the total weight of the cells. Water contains micronutrients and trace elements which are required for the growth of bacteria. It is also highly polar compound.
Raw materials used for culture media
Media are artificially prepared mixtures of various nutrients used to grow and multiply microorganisms (singular medium). Microbiologists use a wide range of culture media to isolate, grow, purify, maintain, and identify microorganisms. A culture must provide adequate carbon, nitrogen, energy, and other nutrients. Nutrient agar is a common laboratory medium used to grow a variety of bacterial species. It is important to note that no single medium is ideal for the growth of all microorganisms.
For the preparation of culture media tap water, pure water or distilled water may be used by dissolving various organic and inorganic compounds. Nearly, 70 to 80 percent of water is present in the protoplasm of the cell and it act as a vehicle for the flow of nutrients. Every enzymatically controlled chemical reaction occurs within the cell in the presence of water. As the copper inhibits bacterial growth, the copper-distilled water can not be used for the preparation of bacteriological or culture media.
Peptone is a complex mixture of partially digested proteins derived from soy meal, casein, fibrin, lean meat, and heart muscle, among other sources. Proteases, amino acids, inorganic salts (phosphates, potassium, magnesium), and growth factors (nicotinic acid, riboflavin) are among the significant components. Peptones serve as buffe and are primarily a source of nitrogenous materials. Peptone is hygroscopic, meaning that air causes it to become sticky. For this reason, it is kept in a tightly closed container.
Yeast extract is prepared from cells of baker’s yeast or Saccharomyces. It consists of carbohydrates, amino acids, growth factors of vitamin B group and inorganic salts. Yeast extract is primarily used as a source of vitamins and can be alternate for meat extract.
Meat extract is prepared from fresh lean meat by hot water extraction process. Meat extract contains gelatin, peptones, proteases, amino acids, creatine, creatinine, purines, mineral salts, carbohydrates and growth factors includes thiamine, nicotinic acid, riboflavin, pyridoxine and pantothenic acid.
Agar is a polysaccharide obtained from seaweeds algae of class Rhotophyta. Agar is mainly taken from the algae called Agarophytes which includes Gelidium, Gracilaria, Hyphea, Gelidiella, Ceramium etc.
Agar is a mixture of two polysaccharides such as agarose (70%) and agaropectin (30%). It also contains some other components salts like calcium, chloride, magnesium, sulphate, iron etc. Agar is commonly used for the preparation of solid media.
We have learned about, what are the various nutritional requirements for the growth of bacteria, bacteria need adequate nutrition, optimum pH, temperature and oxygen. Microorganisms have been cultivated in laboratories using appropriate artificial media that contain sources of carbon, nitrogen, hydrogen, oxygen, phosphorous, and other elements in very small quantity.
Classification of bacteria can be done on the basis of their nutritional requirement like source of energy, source of electron, source of carbon, nitrogen and etc. Raw materials used for culture media includes water, peptone, yeast extract, meat extract and agar.
Frequently asked questions
What are the various nutritional requirements need for the growth of bacteria?
Source of energy, source of electrons, source of carbon, nitrogen, sulphur, phosphorus, mineral salts, growth factors or bacterial vitamins and water these are the various nutritional requirements for the growth of bacteria.
What are the components of bacteriological media?
The various components of bacteriological media include water, peptone, yeast extract, meat extract and agar.