Microbiology – Chapter 5 – Microbial growth
5.1 Binary fission, budding and biofilms
Growth; result of cell division; increase in number of cells
Binary fission; cell division following enlargement of a cell to twice its
minimum size.
Septum; partition that forms between dividing cells.
Cell generations and generation time
Generation (doubling) time; time required for microbial cells to double in number.
It is dependent on species, growth medium and incubation conditions.
Budding cell division
Cell division in bacteria mostly occurs by binary fission, but budding is another
example.
Binary fission; equal cell growth; yield 2 equivalent cells; new cell wall material
throughout the whole cell
Budding; unequal cell growth; forms a new daughter cell with mother cell retaining its
original identity; new cell wall material from a single point.
Biofilms
Biofilms is an attached polysaccharide matrix containing embedded bacterial cells.
(laag micro-organisme omgeven door zelfgeproduceerd slijm vastgehecht aan
oppervlak)
They are a common growth form for bacteria in nature because the intensely
interwoven nature of the structure prevents harmful chemicals from penetrating.
7.3 Cell division and Fts proteins
The divisome
Some key proteins are essential for cell division in prokaryotes.
The proteins interact to from the divisome (cell division apparatus)
• FtsZ; forms a ring around center of cell; related to tubulin
• ZipA; anchor that connects FtsZ ring to cytoplasmic membrane
• FtsA; helps connect FtsZ ring to membrane and also recruits
other divisome proteins; related to actin
Min proteins and cell division
MinCD; proteins that inhibit FtsZ ring formation
MinE; proteins push minCD to the poles.
Min proteins ensure that the divisome forms only a the cell center
and not at the poles, there is MinCD which inhibit FtsZ ring
formation.
7.4 MreB and cell morphology
Proteins that from the cell cytoskeleton.
Cell shape and MreB
MreB; is the major shape-determining factor
• It forms simple cytoskeleton in Bacterial
• Forms spiral-shaped bands around the inside of a rod-shaped cell
, • Not found in coccus-shaped bacteria
The filament structure of MreB move from one side to
another, within the cytoplasm. MreB filaments localize the
synthesis of new peptidoglycan at points where the
filaments contact the cytoplasmic membrane. → new cell
wall material grows out along the length of the cell
In cocci; cell wall grows out in opposite direction from FtsZ
7.5 Peptidoglycan biosynthesis
Insertion of new peptidoglycan
Synthesis of new peptidoglycan during growth requires the
controlled cutting of preexisting peptidoglycan.
Bactoprenol (lipid carrier molecules);
• C55 alchohol
• Binds the N-acetylglucosamine/N-acetylmurarmic
acid/pentapeptide peptidoglycan precursor.
Bactoprenol transport peitodyglcan precursor across cytoplasmic
membrane by rendering them hydrophobic to pass through membrane.
Once outside the cell bactoprenol interacts with enzyme
transglycosylases;
• That insert peptidoglycan precursors into a growing point in the cell
wall.
• Catalyze glyosidic bond formation
Enzymes autolysins; create small openingsin the peptidoglycan, at the
beginning of FtsZ ring.
Transpeptidation
Final step in peptidoglycan synthesis (cell wall synthesis)
Forms the peptide cross-links between muramic acid residues in
adjacent glycan chains.
Formation of peptide bridge is inhibited (not broken!) by the antibitotic
penicilin
Reaction is exergonic (energy is released).
5.2 Quantitative aspects of microbial growth
During cell division the total cell number and mass double.
Most prokaryotic microbes have shorter generation times than eukaryotic
microbes
Plotting growth data
Exponential growth; growth of a microbial population in which cell
numbers double within a specific time interval (doubling time)
5.1 Binary fission, budding and biofilms
Growth; result of cell division; increase in number of cells
Binary fission; cell division following enlargement of a cell to twice its
minimum size.
Septum; partition that forms between dividing cells.
Cell generations and generation time
Generation (doubling) time; time required for microbial cells to double in number.
It is dependent on species, growth medium and incubation conditions.
Budding cell division
Cell division in bacteria mostly occurs by binary fission, but budding is another
example.
Binary fission; equal cell growth; yield 2 equivalent cells; new cell wall material
throughout the whole cell
Budding; unequal cell growth; forms a new daughter cell with mother cell retaining its
original identity; new cell wall material from a single point.
Biofilms
Biofilms is an attached polysaccharide matrix containing embedded bacterial cells.
(laag micro-organisme omgeven door zelfgeproduceerd slijm vastgehecht aan
oppervlak)
They are a common growth form for bacteria in nature because the intensely
interwoven nature of the structure prevents harmful chemicals from penetrating.
7.3 Cell division and Fts proteins
The divisome
Some key proteins are essential for cell division in prokaryotes.
The proteins interact to from the divisome (cell division apparatus)
• FtsZ; forms a ring around center of cell; related to tubulin
• ZipA; anchor that connects FtsZ ring to cytoplasmic membrane
• FtsA; helps connect FtsZ ring to membrane and also recruits
other divisome proteins; related to actin
Min proteins and cell division
MinCD; proteins that inhibit FtsZ ring formation
MinE; proteins push minCD to the poles.
Min proteins ensure that the divisome forms only a the cell center
and not at the poles, there is MinCD which inhibit FtsZ ring
formation.
7.4 MreB and cell morphology
Proteins that from the cell cytoskeleton.
Cell shape and MreB
MreB; is the major shape-determining factor
• It forms simple cytoskeleton in Bacterial
• Forms spiral-shaped bands around the inside of a rod-shaped cell
, • Not found in coccus-shaped bacteria
The filament structure of MreB move from one side to
another, within the cytoplasm. MreB filaments localize the
synthesis of new peptidoglycan at points where the
filaments contact the cytoplasmic membrane. → new cell
wall material grows out along the length of the cell
In cocci; cell wall grows out in opposite direction from FtsZ
7.5 Peptidoglycan biosynthesis
Insertion of new peptidoglycan
Synthesis of new peptidoglycan during growth requires the
controlled cutting of preexisting peptidoglycan.
Bactoprenol (lipid carrier molecules);
• C55 alchohol
• Binds the N-acetylglucosamine/N-acetylmurarmic
acid/pentapeptide peptidoglycan precursor.
Bactoprenol transport peitodyglcan precursor across cytoplasmic
membrane by rendering them hydrophobic to pass through membrane.
Once outside the cell bactoprenol interacts with enzyme
transglycosylases;
• That insert peptidoglycan precursors into a growing point in the cell
wall.
• Catalyze glyosidic bond formation
Enzymes autolysins; create small openingsin the peptidoglycan, at the
beginning of FtsZ ring.
Transpeptidation
Final step in peptidoglycan synthesis (cell wall synthesis)
Forms the peptide cross-links between muramic acid residues in
adjacent glycan chains.
Formation of peptide bridge is inhibited (not broken!) by the antibitotic
penicilin
Reaction is exergonic (energy is released).
5.2 Quantitative aspects of microbial growth
During cell division the total cell number and mass double.
Most prokaryotic microbes have shorter generation times than eukaryotic
microbes
Plotting growth data
Exponential growth; growth of a microbial population in which cell
numbers double within a specific time interval (doubling time)
