Distinct, ecotype-specific genome and proteome signatures in the marine cyanobacteria Prochlorococcus.
BACKGROUND
The marine cyanobacterium Prochlorococcus marinus, having multiple ecotypes of distinct genotypic/phenotypic traits and being the first documented example of genome shrinkage in free-living organisms, offers an ideal system for studying niche-driven molecular micro-diversity in closely related microbes. The present study, through an extensive comparative analysis of various genomic/proteomic features of 6 high light (HL) and 6 low light (LL) adapted strains, makes an attempt to identify molecular determinants associated with their vertical niche partitioning.


RESULTS
Pronounced strand-specific asymmetry in synonymous codon usage is observed exclusively in LL strains. Distinct dinucleotide abundance profiles are exhibited by 2 LL strains with larger genomes and G+C-content approximately 50% (group LLa), 4 LL strains having reduced genomes and G+C-content approximately 35-37% (group LLb), and 6 HL strains. Taking into account the emergence of LLa, LLb and HL strains (based on 16S rRNA phylogeny), a gradual increase in average aromaticity, pI values and beta- & coil-forming propensities and a decrease in mean hydrophobicity, instability indices and helix-forming propensities of core proteins are observed. Greater variations in orthologous gene repertoire are found between LLa and LLb strains, while higher number of positively selected genes exist between LL and HL strains.


CONCLUSIONS
Strains of different Prochlorococcus groups are characterized by distinct compositional, physicochemical and structural traits that are not mere remnants of a continuous genetic drift, but are potential outcomes of a grand scheme of niche-oriented stepwise diversification, that might have driven them chronologically towards greater stability/fidelity and invoked upon them a special ability to inhabit diverse oceanic environments.
Paul
Sandip
S
Structural Biology & Bioinformatics Division, Indian Institute of Chemical Biology, 4, Raja S C Mullick Road, Kolkata - 700 032, India.
Dutta
Anirban
A
Bag
Sumit K
SK
Das
Sabyasachi
S
Dutta
Chitra
C
D001482:Base Composition; D016000:Cluster Analysis; D055028:Comparative Genomic Hybridization; D004269:DNA, Bacterial / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D017753:Ecosystem; D019143:Evolution, Molecular; D014644:Genetic Variation; D016680:Genome, Bacterial; D015999:Multivariate Analysis; D048929:Prochlorococcus / Q000235:genetics*; D020543:Proteome / Q000235:genetics*; D017422:Sequence Analysis, DNA
D004269:DNA, Bacterial; D021901:DNA, Intergenic; D020543:Proteome