Biology Reference
In-Depth Information
C
HAPTER
2
C
HAPTER
GENOMES
I. METHODS
81
II. GENOMES SEQUENCED
90
III. CATEGORIES OF GENES
103
IV. PHYLOGENOMICS
130
Microbial genetics has witnessed rapid and very dynamic changes during the past two decades.
Starting from genes to clones, a number of individual genes in diverse microbial species have been
identifi ed and genetic engineering techniques have enabled plant and animal scientists to produce
genetically modifi ed organisms. The emergence of 16S rRNA as a molecular marker for classifi cation
and identifi cation of microorganisms ushered in a new phase to establish phylogenetic relationships.
Due to a number of inadequacies, pitfalls and unresolved taxonomic puzzles, the choice fell on
a group of housekeeping genes. Soon after, the whole genome sequencing projects added a new
dimension to our understanding of genomes of microorganisms and genome-based phylogeny
came into existence. This is known as 'Phylogenomics'. The fi rst landmark is the publication of
complete genome sequence of
Haemophilus infl uenzae
in 1995 and this event transformed biology into
a throughput endeavour (Fleischmann
et al
., 1995). The current rate of sequencing of prokaryotic
genomes is 20 sequenced genomes per every month. By the end of March, 2009 a total of 1775
prokaryotic genomes have been sequenced that are available at National Center for Biotechnology
Information (NCBI) genome database (Ahmed, 2009). Thus the study of genomes of microorganisms
(genomics in the case of microbial species or metagenomics in the case of whole communities) can
be complemented with the study of mRNAs (also known as transcriptome, transcriptomics) or
proteins (proteome, proteomics). A study of these three areas requires a large sequencing capability
and very powerful bioinformatics tools to organize and study the massive amount of information.
Undoubtedly, the massive synergistic efforts put all over the world for human genome sequencing
project left behind sequencing capabilities and bioinformatics resources that are readily available
by the click of the mouse.
