Friday, January 29, 2016

Bio (4): BACTERIA....

In 1995, the first bacterial genomes were sequenced
First bacterial genome to be sequenced: H. influenzae
Average protein coding content of a bacterial genome is 40 to 97 %
A typical bacterial genome is around 5 million bp, encodes about 5000 proteins
Largest genome is Sorangium cellulosum strain So0157-2, has 14,782,125 bp, contains 11,599 genes

Smallest genome is Candidatus Nasuia deltocephalinicola strain NAS-ALF; has 112,091bp, codes for only 137 proteins
The GC content of the finished bacterial genomes ranges from a bit less than 15% to about 85%
Extremophiles: thermotolerant, psychrotolerant, and psychrotrophic bacteria 
Members of a species are not necessarily “equal” or even similar, in terms of their (protein-coding) gene content  
Depending on the species, the variation in gene content and genome size can be quite considerable, with some pan-genomes, like E. coli, being very “open”; other pan-genomes, such as that for Bacillus anthracis, contain very few extra genes, and can be considered “closed”.
Species can vary by more than a megabase
e.g.Haemophilus influenza HK1212 (1.0 mb) versus F3047 (2.0 mb)
     Burkholderia pseudomallei THE (6.3 mb) versus MSHR520 (7.6 mb)
Core gene families :Families with at least one member in at least of 95% of genomes
Serratia symbiotica str. Cinara cedri has a protein-coding density of 38%, is an insect co-symbiont, having 58 pseudogenes.
Redundancy arise from gene duplications
Repeat sequences and parasitic DNA that seem to bear no function to the organism.
Bacterial genomes are not always evolving towards optimal efficiency
Increased number of tRNAs and rRNAs is correlated with a faster growth rate
Insertions and deletions arise from recombination events
All bacterial genomes have at least one copy of the 23S, 16S and 5S rRNA genes.
Genetic code allows for 62 possible anticodons for tRNAs, but since these have to cover only 20 essential amino acids, the theoretical minimum for a genome would be 20 tRNA genes.
The number of anticodons identified per genome has not exceeded 47 (out of 62 possible), and averages between 33 and 35
Bacteria control  mobile elements through post-segregation killing systems

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