Growth and Physiology of Bacteria

1. Growth and Physiology of Bacteria

2. Chromosome replicates and cells elongate Chromosomes separate and cytoplasmic membrane and cell wall invaginates Cross-wall formation complete Daughter cells separate Bacterial replication Binary Fission

3. Origin DNA replication Terminus Chromosome replication • Chromosome replication initiates cell division • DNA replication is initiated at the origin and proceeds in both directions until it reaches the terminus • In rapidly growing cells the newly formed chromosome will itself start to replicate before cell division

4. Chromosome replication • For a DNA molecule to replicate, it must have at least one functional ori. • This is where the replication bubble initiates; the two replication forks move away from one another and around the chromosome. • The forks collide in the region of the chromosome known as the terminator. • At the end of replication, two sister chromosomes are entangled with one another, they are concatenated. • They are untangled by the enzyme topoisomerase, which can pass one double-stranded DNA molecule through another

5. Bacterial growth • Increase in number of cells • Reproduce by binary fission • Daughter cells of equal size • Cells may or may not separate after division • Cocci: plane of division may be the same or different at each division • Produce characteristic morphology Streptococci Staphylococci

6. Measurement of bacterial growth In liquid media • Turbidity • Absorbance of light = Spectrophotometer • Count particles • Microscopically: counting chamber • Electronic particle counter In or on solid media • Serial dilution

7. Generation time • Each time bacteria divide the population doubles • The time taken for doubling to occur is called the generation or doubling time • Under optimum conditions the doubling time is characteristic of each bacteria • Doubling time is greatly affected by the culture conditions • Salmonella typhimurium generation times • In vitro 20min • In vivo 6 -20h

8. Organism Vibrio Escherichia coli Bacillus subtilis Pseudomonas putidia Mycobacterium tuberculosis Doubling time (min) 9.6 22.8 25.8 45 360 Bacterial growth rates Microorganisms grow very rapidly Microorganisms grow slower in vivo Escherichia coli doubling time in the gut ~ 12 h

9. Exponential bacterial growth

10. Bacterial growth curve Stationary phase Log phase Total bacteria Log No. of Bacteria Viable bacteria Lag phase Time

11. Bacterial growth curve Prokaryotic cells have come to regulate these syntheses to produce only those enzymes and other cellular components required for metabolism and growth in a particular environment. Synthesis of cellular components is, energetically speaking, an expensive process Glucose broth Glucose broth Lactose broth

12. Requirements for Bacterial Growth • Physical requirements • Temperature • PH • Osmotic pressure • Gaseous requirements • Nutrients

13. Effect of Temperature on Bacterial Growth • Bacteria can grow over a range of temperatures • All bacteria have an optimum growth temperature • Most pathogenic bacteria are mesophilic (optm. temp ~ 37OC • Temperatures above the optimum growth temp. are more deleterious than lower temps Bacterial growth rate Optimum growth temp Temp

14. Effect of pH on bacterial growth Optimum growth temp Bacterial growth rate • Bacteria can grow over a range of pH values • All bacteria have an optimum growth pH • Most pathogenic bacteria are neutrophilic (opt. pH ~ 7) • Products of bacterial metabolism are often acidic. Lower pH of growth medium • Some bacteria grow at pH 2 (stomach acid) pH

15. Cytoplasmic membrane loss of water Plasmolysis Cell wall Effect of osmotic pressure on bacterial growth • Each bacterial group grows best in media at a particular osmolarity • Cytoplasm in most bacteria has a greater osmolarity than its environment • Water is prevented from moving into the cell by the rigid cell wall • In hypertonic media, water will leave the cell and results in plasmolysis

16. Only grow in the presence of O2 Obligate Aerobes Mycobacterium Only grow in the absence of O2 Obligate Anaerobes Clostridium tetani Only grow in reduced concentrations of O2 Campylobacter jejuni Microaerophiles Growth is best in the presence of O2 but can grow anaerobically Salmonella Facultative Anaerobes Gaseous requirements: O2

17. Physical requirements for bacterial growth • Temperature • Most 37°C – mesophilic • 4°C Listeria, Yersinia – food poisoning • 42°C Campylobacter jejuni – thermophilic • pH • Most pH7 – neutrophilic • Helicobacter pylori grows at pH2 – acidophilic • Fungi – lower pH than bacteria • Osmotic pressure • Most bacteria inhibited at high osmolarity • Staphylococcus aureus grows in 10% NaCl

18. Nutrient requirements • Pathogenic Bacteria require a source of: • Organic carbon • Nitrogen • Sulphur • Phosphorus • Potassium • Magnesium • Calcium • Trace elements • Iron, Zinc, Copper, Molybdenum • Some require organic growth factors • NAD or NADP (V factor), e.g. Haemophilus

19. Availability of iron in vivo • Levels of free iron below that necessary to support bacterial growth. • Extracellular: • Transferrin and lactoferrin. • Intracellular: • Haemoglobin, cytochromes. • Pathogenic bacteria have iron uptake systems.

20. Fe3+ Fe3+ Iron uptake systems of bacteria TF or LF binding protein Siderophore Bacteria enters low iron environment of host tissues Transferrin or Lactoferrin binding protein Ferric siderophore receptor Siderophore Fe3+ Fe3+ Fe3+