Classification of bacteria on the basis of temperature

Factor affecting growth of bacteria

Various factor affects bacterial growth which in turn are responsible for producing the diverse type of microorganisms in nature. The growth of a microorganism in nature is influenza by no. of factors such as temperature, p^h, oxygen concentration, water availability, nutrition and no. of other environmental factors. It is affected by many factors. Some important that affect growth are:

Nutrients: The nutrients which are required for growth taken from the external source is called essential nutrients. It is basically of two types:

Macronutrients: they consist of C, P, S, K, Ca, Na, Fe, N. Among these C, O, H, S and P are components of micro molecules i.e Proteins, carbohydrate, lipids etc.

Micronutrients: they are required in the trace amount and consist of Cr, Co, Cu, Mo, Se and Zn etc. Trace elements usually required for catalysis reaction and maintenance of protein structure.

If cultivation medium is rich in growth promoting nutrients, growth occurs faster. The decrease in nutrient concentration decreases, the growth rate of bacteria. Different bacteria require different types of nutrients and growth faster for their growth. The growth rate of the organism with the increase in concentration of substrate up to certain level, then growth remains constant.

Temperature: It is one of the most important environmental factor affecting growth and survival of microorganisms.Microorganism differs widely in their temperature required.Since all processes of growth are dependent on chemical reactions and the rate of these reactions are influenced by temperature. It affects the growth of MOS by various ways. The lowest temp that allows the growth in minimum temp and the highest temp that allows the growth is called maximum temperature for that bacteria. There is no growth below minimum and above maximum temp. Below the minimum temperature, cell membrane become stiff so growth cannot transport nutrient and cannot develop proton gradient. So growth cannot occur at that temp. At higher temp denaturation of protein and enzyme and thermal lysis of cell occur,so growth doesn't occur above maximum temperature.When temperature increase growth of microorganism increases slowly and growth becomes maximum at the certain temperature and on further increasing the temperature, the growth rate decreases abruptly.The temperature at which growth is maximum is called optimum temperature for growth.With increases in the temperature, the rate of various cellular and metabolic activity increases so growth increase with temperature.But above the certain temperature,growth rate decrease because at higher temperature denaturation of protein occurs.

The lowest temperature at which organism grow is the minimum growth temperature.Most of the organism will survive for a varying length of time below this temperature,but will show negligible growth.The minimum growth temperature is difficult to determine precisely,because of an increase in generation time.

Cardinal temperature: For every organism, there is the minimum temperature below which no growth occurs,on the optimum temperature the growth is most rapid and a maximum temperature above which growth is not possible.These temperatures are called cardinal temperature are general characteristics of each type of organism.

Classification of bacteria on the basis of temperature required

On the basis of temperature, requirement bacteria are divided as follows

Psychrophiles: A psychrophiles can be defined as the organism with an optimum growth temperature of 15 C or lower,maximum growth temperature below 20C and a minimum growth temperature at 0C or lower.They are found in an environment that are constantly cold such as in polar regions,deep ocean water and in refrigerated food.These organisms can be killed at room temperature or by brief warming eg Vibrio,Pseudomonas,Bacillus psychrophilus,Vibrio marinus strain MP-1.

Psychrotrophs/psychrotolerant: Organism that grows at 0C but has optima of 20-40 are called Psychrotolerant.They are much more widely distributed than psychrophiles and can be isolated from soil and water in the temperate climate as well aa meat,milk,vegetable,fruit etc. eg Pseudomonas species,Lischeria monocytogenis.

Mesophils: It grows best within the temperature range of approximately 25-40C.Mesophiles are found in warm blooded animals and in a terrestrial or aquatic environment.In temperate and tropical areas, all bacteria that are pathogenic for human and warm-blooded animals are mesophiles.Most pathogenic mesophiles best at about body temperature eg E. coli,Klebsiella,Streptococcus etc.

Thermophiles: Organism with optimum growth temperature is above 45C are called thermophiles and those whose optimum is above 80C are called hyperthermophiles.Eg (Thermosulfabacterium,Aquifex,Themocrinis)Eg of thermophiles are Bacillus Streptococcus thermophiles,Bacillus steraro-thermophilus,Thermaoacttinomycetes etc.Thermophiles may be isolated from hot springs,tropical soil,composed piles etc.Thermophiles are of industrial importance because they synthesized heat tolerant metabolites.Various thermophiles are used to produce heat resistant enzyme.For eg tag polymerase is a heat resultant enzyme extracted from thermous aquatics.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.