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