Binary fission & growth curve

Growth & binary fission in Bacteria

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

Binary fission
The growth and division is increased or the synthesis of all cellular constituents from extra cellular environment - the ultimate results of this Is increased in cell size mass and replication &segeration of bacterial DNA and formation of septum which divide the cell in to two progeny cells, the process is coordinate by bacterial membrane perhaps by means mesosomes.
The replication of bacterial genetic (DNA):
During cell growth the DNA replication by process known semi-conservative replication this take place at replication fork, separate helices of DNA act as templates for the new daughter strands. The initiation of replication fork and subsequent DNA polymerase , each daughter cell receive an original strand plus a newly synthesis strand.

Role of mesosomes in binary fission :
cytological electron microscope of bacterial cell wall studies suggest that the mesosomes is involved in cell division regarding
1- the splitting of the chromosome and the
2- initiation of the cytoplasmic membrane and cell wall that forms the two daughter cells


Cell division sequence: there are four stage :
1-cell elongates and DNA is replicated.
2-cell wall &plasma membrane begin to constrict
3- cross-wall forms completely separating the two DNA
Copies
4-cells separate.

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 & multiply 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 accelerated phase or logarithmic

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 phase .

2. 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

Techniques use to measure the growth of bacteria
growth of bacteria population ;
first technique determine the viable number of cells or colony-forming unite using microscopic count &dilution & pouring plating,
.the second technique determine the total count
microorganisms and measures both living and death cells using photoelectric colorimeter method
Bacteria have specific structure and contain many organism. characteristic through which can be differentiated from other
capsule is the main component in bacteria ,the chemical composition are different between many microorganisms .It is mostly polysaccride and some polypeptide and other is polysaccride and polypeptide, there are two types of capsules
1-microcapsules
2-macrocapsules
1-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 antigenic its, also called somatic antigen
or endo toxic, this capsul is though to be responsible for physiological chang associated with Enteric infection such as
fever, leucopenia followed by the leukocytosis.
2-Macrocapsul:It is extracellular highly viscous slime
that adheres firmly to the cell wall of certain bacteria
it is originate as secretion from the cell membrane and is excreted through the cell wall .the genes responsible for encoding such capsule may be present on chromosome or plasmid.
Function of capsul:
1-capsul 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 factors,& antigenic
Pili:They are small structure about 100 and 300 nm long (1.5 u).these structure surround by the cell & vary in number between 100-200 per cell , they are protein in nature , associated with gram negative bacteria , they are presence in both motile & motile bacteria , originate probably from cytoplasmic membrane

F –pili:
There are associated with fertility (F+)and bacterial conjugate processes. They form abridge in conjugation between bacterial cells , The pili are refereed to as sex or F- type pili and are associated in the transfer of nucleic material from male to femal cells , also may serve as receptors for bacterial viruses.
Function of pili
1-Organ of adhesion
2-Hemagglutination
3-They are antigenic
4-Agglutinationm and pellicle formation
5-Conjugation tube through which genetic material is transfered.