microbial nutrition

Microbial nutrition
Growth of bacteria normally refers to an increase in number of an individual cells and a measure of population density from original inoculums .
Nutrients are substances used in biosynthesis and energy production , therefore are required for microbial growth . So, the microbial cells are needing basic requirements as fallow :

A - Nutrient elements
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 macroelements 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 factors :
a- purines and pyrimidines for nucleic acid synthesis .
b- amino acids are needed for protein synthesis .
c- vitamins are small organic molecules that are 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, K etc .

B- Source of energy
Microorganisms can be classified according to :
- Source of carbon
a-Heterotrophs : which use the organic compounds as a source of carbon .
b-Autotrophs : which use the CO2 as a source of carbon .
- Source of energy
1- Phototrophs : which use light as source of energy .
2- Chemotrophs : which use chemical energy.

C-Physical requirements for bacterial growth
There are some factors influence on microbial growth include :-
1- Temperature
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 .

2- Oxygen
a- Obligate aerobes have an absolute requirement for oxygen such as Pseudomonas .
b-Obligate anaerobic : they can not multiply and killing if oxygen is 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 ex. Campylobacter .

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) ex. Vibrio.

Reproduction in bacteria
Bacteria can reproduce through :
1-Binary fission
Binary fission occurs normally under favorable conditions , the cell elongate and becomes constricted at middle, the nucleus divided then constriction increases until the cell is split into two cells , each receiving one nucleus . The time needed for cell to divide into two cells is called generation time and differs according to species and prevailing condition, may be range between 20 minute to 6 hours .
















Exchange of genetic material
In this process , part of the genetic material of a donor cell is transferred to a recipient cell by one of the fallowing mechanisms :

a-Transformation
It is uptake of the naked free DNA of donor bacteria by a recipient bacteria , the taken fragment is incorporated in chromosomal DNA and expressed as a new character in the recipient cell (fig.)







b- Transduction
It is transfer of part of DNA of the donor bacteria to recipient bacteria by bacteriophage (fig.)











c-Conjugation
Conjugation occurs through mating of two bacteria cells one of them carries plasmid ( F + ) and the other is plasmid (F-) . Conjugation is the most common method occur in nature and it is a major phenomenon that is responsible for transfer of antibiotic resistant in bacteria (fig.)
















In biology, symbiosis is defined as "life together "that two organisms live in an association with one another thus , there are at least three types of relationships :

1-Mutualism : When two organisms live in association both of them benefit from their presence together or near each other, their mode of living is known as mutualism, for example genus Rhizobium which form nodules on roots of Leguminous plants , the Rhizobium fixes atmospheric nitrogen and transform to nitrate which are absorbed by the Leguminous plants while the latter provides the nitrogen fixing bacteria with organic food material and growth materials .

2- Commensalisms : A type of symbiosis in which one of the members of this association benefit and the other is not harmed for example the relationship with Staphylococcus epidermidis, a consistent inhabitant of the skin of human, by produces lactic acid that protects the skin from colonization by harmful microbes that are less acid tolerant.











Fig. Staphylococcus epidermidis






3- Parasitisms : In biology , the term parasite refers to an organism that grows, feeds and is sheltered on or in a different hosts . The parasite is termed obligate when it can live only in a host for example viruses and Rickettesia and as facultative when it can live both in a host as well as in free form as saprophytic life for e.g. Bacillus anthraces . Parasites that live inside the body are termed endoparasites whereas those that exist on the body surface are called ectoparasites.



Defnition
Viruses : are biological particles (Latin virus meaning "poison" ) obligate intracellular parasitic microorganisms which are smaller than bacteria and so could passes through bacterial filters, they have not contain nucleus , cytoplasm, cellular structure and no cell membrane , but have genetic material and protein .Viruses are known to be responsible for several disease of man ,animal, plant etc.


General features

1- Virus size:Viruses are only visualized by electron microscopes , they are between
(20 -300) nm in length viruses can pass through bacterial filters.
2-They contain one kind of nucleic acid either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA).
3-Obligate intracellular parasites because viruses do not contain the machinery for replication ,for this the nucleic acid of an infecting virus takes over the control of an infected cell to produced new viral nucleic acids and proteins .
4- No ribosome : viruses can not be synthesize their own proteins , they utilize host cell ribosome during translation.
5- Characteristic shapes : viruses have several shapes like spherical (complex) , helical , rod and polyhedral , sometimes with tails or envelopes .
6- Viruses can be classified according to their :-
a- Morphology (size, shape, types of symmetry, presence of tail or envelope).
b- Biological properties such as pathoginicity , host range which refers to the type of cell in which the viruses are able to replicate in many hostes like animals , plant, insects and bacterial viruses called bacteriophage or bacteria eaters .
c-Type of nucleic acid , deoxyribonucleic acid, ribonucleic acid single or
double stranded, linear or circular .
7- Virus structure : virus particle contains either DNA or RNA, double or single stranded, it lies in center or core of a virus particle surrounding by a protein coat called a capsid ( it protects the nucleic acid genome and mediates the



attachment of the virus to specific receptors on the host cell surface ) made up of protein subunits called capsomer .

8- Some viruses may have an ultimate exterior cover of lipoprotein, the envelope which is largely derived from cytoplasm membrane of the host cell . Enveloped viruses are more sensitive to heat ,detergents and lipid solvents such as alcohol and ether than non- enveloped virus .















Fig. the virus structure




Lytic cycle of T4- phage on E. coli
Viruses can multiply by using host energy and chemical supply to make its own nucleic acid and proteins , these substance are assembled into many viral particles.
There are five steps composed of lytic cycle as fallow :


1- Attachment
The first step in lytic cycle is the attachment or adsorption of phage -T4 when the tail fibers recognize and attaches to specific region on the cell wall of E. coli called receptors site.

2- Entry
In the beginning an enzyme in the tail breaks down the bacterial cell wall in the receptor site, then the sheath of tail contracts and drives the DNA core through the cell wall of E. coli and empty protein coat remains outside has no role in the cycle.





3-Replication
After infection, viral DNA takes over the biosynthetic machinery of the host cell and uses it to produce the parts needed for production of new virus particles ,
viral DNA replaces the host cell DNA as a template for replication to produce more viral DNA and transcription to produce viral mRNA .Viral mRNA are then translated using host cell ribosome into viral proteins (protein coat) .

4- Assembly
The cell becomes a factory for making viruses , the phage DNA and protein are assembled into 200-300 new phage.

5- Release
Lastly, the cell wall membrane breaks down and new phages are released, those newly viruses can infect other cells and begins the cycle over again .


























Fig. Lytic cycle of T4 – Phage in E. coli cell