Nutritional Requirements of Bacteria
Nutritional Requirements of Bacteria: Bacteria may require adequate nutrition, optimum pH, temperature and oxygen for multiplication and growth. Bacteria can be classified into following types on the basis of nutritional requirement.
I. On the basis of energy sources:
(a) Phototrophics which gets energy from photochemical reaction.
(b) Chemotrophic gets energy from chemical reaction.
II. On the basis of their ability to synthesize essential metabolites.
(a) Autotrophic: These are the organisms in which all essential metabolites are synthesized from inorganic sources. They use carbon-dioxide as the main source of carbon and simple inorganic salts e.g., nitrates, nitrites, ammonium sulphate, phosphates etc., to form new protoplasm of the cell.
(b) Hetereotrophic: Here some of the essential metabolities are not synthesized. Organic compounds e.g., protein, peptones, amino acids, vitamins and growth factors are supplied from outside. Most of the bacteria producing disease in man are heteredtrophic.
The other nutritional requirement are as under:
(1) Minerals
These are sodium, potassium, magnesium, calcium, iron, chlorine, zinc, copper, iodine and strontium in traces. These are essential for physiological activities of bacteria.
(2) Gas Requirements
(a) Oxygen: The capacity of bacteria to grow in the presence of oxygen and to utilize it depends on possession of a cytochrome oxidase system.
Aerobes: The aerobe organisms grow only in the presence of oxygen e.g., pseudomodaceae, bacillus, nitrobacter, sarcina etc. They require oxygen as hydrogen acceptor.
Facultative anaerobes: They are the organisms that can live with or without oxygen e.g., vibrio, Escherichia coli, salmonella, shigella and staphylococcus. The micro-aerophilic organisms grow well with relatively small quantities of oxygen e.g., hemophilus.
Obligate anaerobes: The strict anaerobes multiply only in the absence of oxygen e.g., bacteroides, clostridium. They require a sub¬stance other than oxygen as hydrogen acceptor.
The toxicity of oxygen results from its reduction by enzymes in the cell (e.g., flavoprotein) to hydrogen peroxide and even more toxic free radical superoxide. Aerobes and aerotolerant anaerobes are protected from these products by the presence of superoxide dimutase, an enzyme by the presence of catalase. There is one exception to this rule i.e., lactic acid bacteria; aerotolerant anaerobes that do not contain catalase. This group however, relies instead on peroxidases. All strict anaerobes lack superoxide dismutase, catalase and peroxidase. Superoxide dismutase is indispensable for survival in presence of oxygen.
Hydrogen peroxide owes much of its toxicity to the damage it causes to DNA. DNA repair deficient mutants are exceptionally sensitive to hydrogen peroxide, the rec A gene product. Its function is both genetic recombination and repair. It is said to be more important than either catalase or superoxide dismutase in protecting Escherichia coli against hydrogen peroxide toxicity.
(b) Carbondioxide: The metabolic activities of some organisms like Neisseria gonorrhoeae, Brucella abortus are greatly enhanced by the presence of extra amount of carbondioxide in atmospheric air.
(3) Moisture
Bacteria require water for their growth. Dessication may kill most of bacteria.
(4) Accessary Nutritional Requirement
Most often the accessary growth factors are vitamins. The requirement of growth factors differ widely in various bacteria e.g., Organism I Growth factors
N. gonorrhoeae Glutathione
C. diphtheria B-alanine
S. aureus Nicotinic acid, thiamine
H. influenzae Hematin (Co-enzyme I)
They are not synthesized by bacteria and so supplied in media.
Tags: aureus, B-alanine, diphtheria, Glutathione, Gonorrhoea, Hematin, influenzae, Nicotinic acid, thiamine
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