Taxonomic resolution, ecotypes and the biogeography of Prochlorococcus.
Martiny AC, Tai AP, Veneziano D, Primeau F, Chisholm SW
Environ Microbiol. 2008 Nov 11.
In order to expand our understanding of the diversity and biogeography of
ribotypes, we PCR-amplified, cloned and sequenced the
16S/23S rRNA ITS region from sites in the Atlantic and Pacific oceans.
Ninety-three per cent of the ITS sequences could be assigned to existing
clades, although many novel subclades were detected. We
assigned the sequences to operational taxonomic units using a graduated
scale of sequence identity from 80% to 99.5% and correlated
diversity with respect to environmental variables and
dispersal time between the sites. Dispersal time was estimated using a
global ocean circulation model. The significance of specific environmental
variables was dependent on the degree of sequence identity used to define
a taxon: light correlates with broad-scale diversity (90% cut-off),
temperature with intermediate scale (95%) whereas no correlation with
phosphate was observed. Community structure was correlated with dispersal
time between sample sites only when taxa were defined using the finest
sequence similarity cut-off. Surprisingly, the concentration of nitrate,
which cannot be used as N source by the Prochlorococcus
culture, explains some variation in community structure for some
definitions of taxa. This study suggests that the spatial distribution of
ecotypes is shaped by a hierarchy of environmental factors
as well dispersal limitation.
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