growth curve

Growth & Binary fission in Bacteria
Dr. Baha, H. AL-Amiedi
Ph.D.Microbiology
Lecture 2
Binary fission
The growth & division is synthesis &increased in quantity of all cellular constituents from extra cellular environment, the ultimate results of this is increased in cell size &mass and replication & segregation of bacterial DNA and formation of a septum which divides the cell into two progeny cells; . The process is coordinate by bacterial membrane perhaps by means of mesosomes.
The replication of bacterial genetic (DNA):
During cell growth the DNA replicates by process known semiconservative 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 replication is performed by series enzymes coordinated with DNA polymerase, each daughter cell receives an original strand plus a newly synthesis strand .
The replication of bacterial genetic (DNA):
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 ofCell division sequences;

1-Cell elongates & DNA is replicated
2-Cell wall & plasma membrane begin to constrict.
3-Cross-wall forms completely separting the two DNA copies.
4-Cell separate

the chromosome .
2-the initiation of the cytoplasmic membrane and cell wall that forms the two daughter cells

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
1-cell size is larger than in any other phase
2-there is an increased synthesis of RNA but not of DNA
3-the cell are not dividing
4-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 phase
3-stationary phase :
after some time a stage comes when rate of multiplication and death becomes almost equal
. it may be due to;
1-depletion of nutrient
2-accumulation of toxic products
sporulation may occur during this phase Bacteria have specific structure characteristic that 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
Microcapsules: it is thin layer close to outer part of cell wall and it is formed by gram negative bacteria, it is lipopolysacaride protein complex &its antigenic also called somatic antigen or endo-toxic and though to be responsible for physiological change associated with enteric infection such as : fever , leucopenia followed by leukocytosis
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
F –pili:
There are associated with fertility (F+)and
in bacterial conjugation processes. They form abridge in conjugation between bacterial cells. These pili are referred 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.

decline phase :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 transferred.

during this phase population decrease due to death of cells factors responsible for this phase are :
1-Nutritional exhaustion
2- Toxic accumulation
3- Autolytic enzymes involution is common in phase of decline
Techniques use to measure the growth of bacteria population

First technique determine the viable number of cells or colony-forming unite using microscopic count and &pouring plating,
.Second technique determine the total count of microorganisms and measures both living and death cells using photoelectric colorimeter method