Growth of Microorganisms

Ultra – structures & growth in bacteria

Dr. Baha, H. AL-Amiedi
Ph.D.Microbiology
Lecture 2


Growth and division
The growth and division is increased or the synthesis of all cellular constituents from extra cellular nutrients - the ultimate results of this Is increased and being divisions or replication . the growth of bacteria is separate in to two different stages such as elongation in ( increased in mass ) bacillus or increased in volume such as cocci and division of these cells in to two new daughter cells ( binary cell division ) cytological electron microscope of bacterial cell wall studies suggest that the mesosomes is involved in cell division regarding the splitting of the chromosome and the initiation of the cytoplasmic membrane and cell wall that forms the two daughter cells - the bacterical genetic material (Genom ) is arranged in a linear fashion along circular DNA strands the majority of gram positive & gram negative bacteria divided in an identical fashion by binary division which consist of three steps :
1. In bacillus increased in length & volum while cocci increased in volume so nuclear material separated into two equal halves
2. the septum formation as in growth of cytoplasmic membrane and peptide glycan
3. cell separation occur as aresult of hydrolytic cleavage of ingrowing peptiod glycan by specific hydrolytic enzymes
Bacterial growth Curve:
the bacterial growth curve when bacteria are inoculated in a suitable growth medium and provided with all appropriate requirements for maximum growth and division the growth of cells divided into four phases :

1-- lag phase ( phase of adaptation ) " increase in cell size. This phase is characterize by each of the following
a. cell size is larger than in any other phase
b. there is an increased synthesis of RNA but not of DNA
c. the cell are not dividing
d. the unit of metabolism per cell is greater than in any other phase of growth curve

2--log phase : following in crease in size , the cells begin to divide & multply at a geometric rate. lncreased in number of bacteria to the extent that media look turbid to the naked eye
( log phase ) this phase is called eccelerated phase or logarithmic phase the generation time can be measured the generation time for most organism is determined during the early part of the accelerated growth phase during the late part of this phase . some of the cell are drying

3--stationary phase : after some time a stage comes when rate of multiplication and death becomes almost equal .
it may be due to :
A-depletion of nutrient
B-accumulation of toxic products
sporulation may occur during this stage .
4. decline phase : during this phase population decrease due to death of cells factors responsible for this phase are :
I. nutritional exhaustion .
II. Toxic accumulation
III. Autolytic enzymes involution is common in phase of decline

Different techniques used are used to measure the growth of bacteria population ;one technique determine the viable number of cells or colony-forming unite using microscopic counte or pouring
Plating .the secound technique determine the total count of microorganisms and measures both living and death cells using photoelectric colorimeter method




Bacteria have specific structure and contain many characteristic through which can be differatiated from other organism.
capsule is the main component in bacteria ,the chemical composition are different between many micoorganisms .It is mostly polyssacaride and some polypeptide and other is polyssacaride and
polypeptide.There are two types of capsules
1-microcapsules
2-macrocapsules
Microcapsuls:It is thin layer close to outer part of cell wall and it is formed by gram negative bacteria and it can remove without affecting the stability of cell. It is lipopolyscaride protein complex and antigenict its,also
called somatic antigen or endo toxic, this capsul is though to be responsible for physiological chang asso-
ciated with Enteric infection such as fever,leucopenia
followed by the leukocytosis.
2-Macrocapsul:It is extracellular highly viscous slime
thate adheres firmly to the cell wall of certain bacteria
it is orginate as secretion from the cell membrane and is excreted through the cell wall.the genes responsible for encoding such capsul may be present on chromosome or plasmid.
FUNCTION:
1-Macrocapsul protect the cell wall from harmful environment factors
2-it may serve as means of adherence of the micro-
organism to the surface in which present on it.
3-it may aid in blocking the surface of receptors of bacteria to bacteriophage
4-it play as well as antiphagosetic factores,& antigenic
Pili:They are numerous filment short in size(1.5 u)
and peritrichous in distribution . they are considered
organs of adhering to the surface of the other cell of
various animal species this form the basis of hemaggl-
utinine
F pili: There are associated with fertility (F+)and help
in bacterial conjugation processes. They are larger than common and Col I pili
Col I pili :They are associated with colicin factor I
FUNCTION:
1-Organ of adhesion
2-Hemagglutination
3-They are antigenic
4-Agglutinationm and pellicle formation,
5-Conjugation tube through which genetic material is transfered.