MICROBIOLOGIA GENERALE Prokaryotic genomes

The prokaryotic genome

Essential and non-essential genes in the prokaryotic genome

The prokaryotic genome

The chromosome of Escherichia coli

Autoradiograph of intact replicating chromosome of Escherichia coli

Supercoiled DNA

Prokaryotic genomes: Sequencing, sizes, ORF contents and gene distributions

Whole-genome random sequencing and assembly of Haemophilus influenzae Rd Fleischmann et al. Science 269, , 1995 An approach for genome analysis based on sequencing and assembly of unselected pieces of DNA from the whole chromosome has been applied to obtain the complete nucleotide sequence (1,830,137 base pairs) of the genome from the bacterium Haemophilus influenzae Rd. This approach eliminates the need for initial mapping efforts and is therefore applicable to the vast array of microbial species for which genome maps are unavailable. The H. influenzae Rd genome sequence (Genome Sequence DataBase accession number L42023) represents the only complete genome sequence from a free-living organism. H. influenzae DNA was sonicated and fragments with sizes between 1.6 and 2.0 kb purified from an agarose gel and ligated into a plasmid vector to produce a clone library. End sequences were obtained from clones taken from this library, and a computer used to identify overlaps between sequences. This resulted in 140 sequence contigs, which were assembled into the complete genome sequence,

The steps in a whole-genome shotgun sequencing project

Locating possible functional open reading frames (ORFs)

This is a schematic representation of the Escherichia coli O157:H7 EDL933 DNA molecule: chromosome Escherichia coli O157:H7 EDL933. Each color represents a different functional group of genes.

MicroorganismSize (bp)ORFs Mycoplasma genitalium Borrelia burgdorferi Treponema pallidum Helicobacter pylori Staphylococcus aureus Bacillus subtilis Mycobacterium tuberculosis Escherichia coli Pseudomonas aeruginosa Streptomyces coelicolor Prokaryotic genomes

Genome size (megabases) Total ORFs in genome Correlation between genome size and ORF content in prokaryotes Each megabase of prokaryotic DNA encodes about 1000 ORFs

Gene function in bacteria genomes

Functional category of genes as a relative percent of the genome versus total ORFs in the genome

Variations in gene category in Bacteria and Archea

OrganismSize (Mbp)ORFs Saccharomyces cerevisiae 13 (16 chr)5570 Plasmodium falciparum 27 (14 chr)- Encephalitozoon cuniculi2.9 (11 chr)1997 Caenorhabditis elegans97 (6 chr)19099 Arabidopsis thaliana125 (5 chr)25498 Mus musculus2500 (23 chr)30000 Homo sapiens3000 (23 chr)30000? Eukaryotic genomes

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How complete microbial genome sequence data can speed vaccine development

Bacterial metagenomics