1 - Growth

Encourage - antibiotics, bioplastics

• Capable of removing ,man made contaminants in the environments

• - eg. oil spills - microbes that break down long chain hydrocarbons 

Avoid - antibiotic resistance, cyanobacterial blooms 

• Associated with infection and disease 

In vitro = grown in the lab in a medium 

• Doesn’t provide clear pic of what it's like in the wild - they're given all the nutrients they need to survive- natural environment not like this 

Generic strategy of growth:

• Resting state - not very active - some produce spores

Bacteria have small molecules in cell surface that can detect conditions

Signal sent into cell 

Genes turned on or off so they can respond to the environment 

E.coli O14:H4 

• Major 2011 E.Coli outbreak 

• Impacted mainly healthy adults 

• Contaminated salad vegetables - huge economic effect 

• Parthenogenesis - bloody diarrhoea, kidney damage/failure 

• Different from normal E.Coli in gut due to virulence factors 

• Genome sequenced during the outbreak 

• E Coli could bind to colonic tissue 

• Produced shiga-toxins 

• Resistant to many drugs 

• Evaded the immune system 

• Trouble identifying this - clinical microbiology tests didn't test for this type of E.coli 

Caulobacter 

• flagella , proteins on surface detect nutrient gradient - only moves towards nutrients 

• Finds ideal environment - gene expression changes - prostheca  attached to ground creating a sessile stalk 

• When nutrients is low - cells divide creating flagella to move again 

• 

Growing in the lab: 

• Batch 

• Closed 

• No addition or removal of nutrients or culture (except gases) 

• Allows us to synchronise the cells growing in a culture 

• Continuous 

• Open system 

• Continuous addition of medium balanced by removal of culture to balance medium - one problem is contamination

• Overnight culture when cells are in stationary phase - take sample - put into fresh media so they grow at the same time 

LAG PHASE of batch culture 

Cells adapt to new medium 

• Carbon, nitrogen sources 

• Period of non-replication 

• Adjust to the new conditions 

• Synthesise enzymes, RNA etc. 

• Dynamic, adaptive phase that protects the bacteria from potential threats and promotes reproductive flexibility 

Media 

• Complex - always rich, made from peptone or yeast extract, 

• Defined - more than minimal but it is defined - molecules can be quantified 

• Minimal 

LOG PHASE 

• Rapid growth 

• Doubling through bacterial binary fission 

• Number of new bacteria appearing per unit time is proportional to the present population 

• Continuation up until there is a depletion in nutrients 

STATIONARY PHASE

• Nutrient limitation and waste accumulation 

• Secondary metabolism eg. storage compounds, glycogen, antibiotics

• Number of dividing cells is equal to the number of dying cells so there is no overall population growth

• Bioplastics, kinases produced 

• Spore forming bacteria produce endospores 

• Pathogenic bacteria produce substances (virulence factors) which consequently make them pathogenic 

DEATH/DECLINE PHASE 

• Monitored over long period 

• Number of dying cells continues to rise 

• Number of living cells declines exponentially 

• Dying cells lyse/break open and release their contents to the environment -  nutrients now available to other bacteria - this helps spore forming bacteria to survive long enough for spore production 

• Spores can survive in harsh conditions of the death phase and can become growing bacteria when placed in an environment that supports life  

• Continued survival of GASP mutants (growth advantage in stationary phase) 

Cell growth: 

• Some of the peptidoglycan has to be broken down and reassembled for bacteria to grow (elongasome) 

Escherichia coli structure:

• Ribosomes are located at the poles of the cell - protein synthesis occurs here

Peptidoglycan sacculus 

• Structure in the cell wall of most bacteria cells 

• Flexible mesh withstands turgor pressure 

• Extension is tricky 

• Glycan chain broken by lysosome and autolysins 

• Formation of this structure involves the formation of monomeric precursors in the cytoplasm, their transport to the periplasm and polymerisation to form a functional peptidoglycan sacculus 

The cytoplasm 

• Crowded but probably non-uniform

• Axial nucleoid with loops - excludes ribosomes 

• Expression: RNA polymerase active in axial region and possibly loops but translation mainly at peripheral and caps 

• Transertion: 

• Insertion of proteins into wall at peripheral site of expression → multi-protein hyperstructure  

Cell division must sync with DNA replication 

• Bidirectional DNA replication from origin 

• Chromosome separation involves four macrodomains 

• Z rings produced in the centre of the cell →septum 

• Cells first copy DNA

• Meanwhile, replication initiated at origin 

Cell cycle in E. coli 

Poles / end-caps 

• Formed by divisome

• Formed during division by contraction on Z ring - contains FtsZ (tubulin homolog) 

• Some lipids and proteins specifically localise to pole - eg. cardiolipin Caulobacter flagellum 

• Old and new poled ie. ageing - old pole gets misfolded proteins (inclusion bodies) 

• Allows a mechanism for gene expression