The photoheterotrophy is the capacity to use both organic substrates and light energy. The aerobic anoxygenic phototrophic bacteria (AAPB), the proteorhodopsin-containing bacteria (PRB) and the picocyanobacteria (Synechococcus) practice it. Increases in organic carbon exported by rivers and in exposure of sea surface to solar radiations are intensifying in Arctic. Hence, this study area is particulary interesting to understand the role of these bacteria in carbon and light uses. Using multiple approaches in absolute quantification, cultural and molecular diversities, our study is the first to characterize at high resolution scale the photoheterotrophs in the Arctic Ocean. Picocyanobacteria were only detectable in the Mackenzie estuary whereas AAPB and PRB were present throughout the Beaufort Sea. AAPs were strongly linked with river inputs contrasting to PRB, principally oligotrophs. Both distributions of AAPB and PRB exhibited different patterns of those of bacterioplankton suggesting an ecological advantage of the photoheterotrophy in these waters. The AAPB community was dominated by a new Betaproteobacterial clade and Rhodobacterales. Alphaproteobacteria, especially the SAR11 group and SAR116 endemic clades, dominated the PR community. The majority of PRB groups actively expressed the PR suggesting probable benefits. Together, our data highlight the photoheterotrophy is common in Arctic Ocean and suggest that his role could be different depending on the environmental conditions encountered.
