Microbial Growth & Genetics
• Growth of microbial populations• Phases of growth• Replication• Genetic recombination• Mutations
Logarithmic growth
Doublingtime
Growth of microbial populations: Phases of growth
Bacterial Cell Division
• Bacterial genes on a circular chromosome • Some bacteria have one to many plasmids; extra
pieces of DNA• Plasmids carry extra genes: antibiotic resistance,
fertility factor, virulence plasmids for toxins
Genomes
• Mycoplasma is580,000 base pairs, smallest known cellular genome
• E. coli is 5,000,000 base pairs
• Propionbacteriumacnes, is 2,560,000 base pairs with 2333 genes
Binary Fission
Bacterial Genetics and Evolution
• Genotype = genetic make-up• Phenotype = physical traits
• Phenotype determined by gene expression
Bacterial Genetic recombination
• Exchange of DNA in bacteria• Horizontal gene transfer: same generation• Three ways: transformation, conjugation,
transduction
Transformation: exogenous DNA
Some bacteria suck up DNA from environmentCommon in soil - decomposition, lots of DNAImplications in a hospital… what do you think?
ConjugationExchange of plasmid by sex pilusDonor sex pilus attaches to recipientCopy of plasmid moves through pilusAntibiotic resistance on plasmids
TransductionBacterial genes picked up by virusesHappens as bacteria fall apart during lysisCarried to another bacteria during next infectionAny bacterial gene – antibiotic resistance
In transduction, the trait acquired is FROM the previous host BACTERIUM. The virus acts ONLY as the CARRIER.
Lysogenic ConversionBacteria acquire new traits from viruses (phage) Viruses inject their genes into bacteriaExpress during lysogenic phaseExample: Diphtheria toxin
In lysogenic conversion, the trait acquired is FROM the virus.
MutationsNaturally occur while copying DNARate - one mistake per million base pairsMutagens enhance natural error ratee.g. chemicals, UV, X-rays…Mutagenicity is correlated with carcinogenicity
Ames Test: Detection of chemical mutagens