Global genetic capacity for mixotrophy in marine picocyanobacteria.
Alexis P. Yelton, Silvia G. Acinas, Shinichi Sunagawa, Peer Bork, Carlos
Pedrós-Alió, Sallie W. Chisholm
Scientific Data, submitted, 2015
The assimilation of organic nutrients by autotrophs, a form of mixotrophy,
has been demonstrated in the globally abundant marine picocyanobacterial genera
Prochlorococcus and Synechococcus. However, the range of compounds used and the
distribution of organic compound uptake genes within picocyanobacteria is
unknown. Here we analyze genomic and metagenomic data from around the world to
determine the extent and distribution of mixotrophy in these phototrophs.
Analysis of forty-nine Prochlorococcus and eighteen Synechococcus isolate
genomes reveals that all have the transporters necessary to take up amino acids,
peptides, and sugars. However, the number and type of transporters and
associated catabolic genes differ between different phylogenetic groups with
low-light IV Prochlorococcus, and 5.1B, 5.2 and 5.3 Synechococcus strains having
the largest number. Metagenomic data from sixty-eight stations from the Tara
Oceans expedition also indicate that the genetic potential for mixotrophy in
picocyanobacteria is globally distributed and differs between clades.
Phylogenetic analyses implicate gradual organic nutrient transporter gene loss
in the observed clade differences. The phylogenetic differences in genetic
capacity for mixotrophy combined with the ubiquity of picocyanobacterial organic
compound uptake genes suggests that mixotrophy plays a more central role in
their ecology than was previously thought.