Microbial nutrition
Growth of a living organism, may be defined as an increase in mass or size in any direction accompanied by synthesis of macromolecules, leading to the production of a newly organized structure. Growth when applied to bacteria normally refers to an increase in number of individual cells and so , is a measure of population density from original inoculums. Bacterial growth can be very rapid for ex. culture of Escherichia coli can double in size in 20 minutes in a rich medium . so , to obtain energy and construct new cellular components, organisms must have a supply of raw materials or nutrients.
Nutrients : are substances used in biosynthesis and energy production , therefore are required for microbial growth.
Common nutrient requirements
Microbial cell require a basic nutrient elements for growth and replication as fallow :
1- Microbial cell composition is made up of few major elements like carbon , oxygen , hydrogen, nitrogen , sulfur , phosphorus , potassium , calcium, magnesium and iron are called macro elements because they are required in large amounts as components of carbohydrate , lipid , protein , nucleic acids synthesis.
2- Microorganisms require several micronutrients like manganese , zinc , cobalt , nickel and copper are available in nature , have many roles in the cells as a part of enzymes , cofactors that make to catalysis of reaction and maintenance of protein structure .
3- Growth factors are organic compounds require as an essential cell components and can not synthesis by M.O. There are three major classes of growth factor :
a- purines and pyrimidines for nucleic acid synthesis .
b- amino acids are needed for protein synthesis .
c- vitamins are small organic molecules that usually make –up all or part enzymes and cofactors that are needing in very small amounts to sustain growth such as folic acid , biotin , vitamins B12 and K etc .
Some bacteria for ex. E. coli do not require any growth factors , they can synthesize all essential purines, pyrimidines, amino acids and vitamins, starting with their carbon source, as part of their own intermediary metabolism, while other bacteria like Lactobacillus requires purines, pyrimidines, vitamins and several amino acids in order to grow.
Aspects of bacterial growth
Cell multiplication requires a source of energy and raw materials for synthesis of cell components . Microorganisms can be classified as either heterotrophs or autotrophs with respect to their source of carbon & for phototrophs , chemotrophs with respect to their source of energy as fallow:
1- Photoautotroph :- Which use light energy and CO2 as a source of carbon.
2- Photoheterotrophs :- Which use light energy and organic compounds as a source of carbon.
3- Chemoautotrophs :- Which use chemical energy and CO2 as a source of carbon.
4- Chemoheterotrophs :-Which use chemical energy and organic compounds as a source of carbon.
Physical requirements for bacterial growth
There are some factors influencing microbial growth include :-
1- Temperature
Environmental temp. affects on M.O like other organisms because they are usually unicellular and their temp. varies with that of the external environment . M.O can be placed in fours classes based on their temp. range for growth:
a- Psychrophiles:- M.O grow well at 0c° and have an optimum growth temp. between( 15-20) c° such as Vibrio.
b- Mesophiles:- M.O grow optimally around (20-45)c° such as all human pathogen for ex. Staphylococcus aureus , Enterococcus.
c- Thermophiles:- M.O they can grow at temp of 55c° or higher for ex. Bacillus , Sulfolobus .
d- Extreme thermophiles:- M.O grow optimally above 80c° for ex. Pyrolobus fumarri.
2- Oxygen
a- Obligate aerobes have an absolute requirement for oxygen such as Pseudomonas .
b-Obligate anaerobic : they can not multiply if oxygen is present and it s kill bacteria if present such as Clostridium .
c- Facultative anaerobes :- can utilize oxygen if it s available but they can grow in it s absence such as Staphylococcus .
d- Microaerophilic organisms :- require small amounts of oxygen (2-10)%, but higher concentrations are toxic for example Campylobacter .
e- Aero tolerant organisms :- grow in the presence or absence of oxygen but they derive no benefit from the oxygen such as Enterococcus.
3- PH
a- Neutrophiles :- most species of bacteria grow best in a medium with a pH 7.2 such as E. coli.
b- Acidophile :- include bacteria tolerate highly acidic condition pH between (0-5) such as Lactobacilli
c- Alkalophiles :- Grow optimally under alkaline condition PH about (8.5-11.5) for example Vibrio.
Reproduction in bacteria
In bacteria the genetic material is organized in a continuous strand of DNA , this circle of DNA is localized in an area called nucleoide , bacterial cell may include one or more plasmid that can replicate independently and not responsible for reproduction of the microorganisms .
Bacteria can reproduce through :
1-Binary fission
It is occurs normally under favorable conditions , the cell elongate and becomes constricted at middle, then the nucleus divided and the constriction increases until the cell is split into two cells , each receiving one nucleus in generation time that meaning the time needed for cell to divide into two cells and differs according to species and prevailing condition, may be range between 20 minute to 6 hours .
2- Conidia
It occurs in members of certain families belonging to Actinomycetes e.g., Streptomyces , the ends of the filaments become septated forming a chain of conidia similar to those produced by true fungi .