Description: Background Although the importance and widespread occurrence of iron limitation in the contemporary ocean is well documented, we still know relatively little about genetic adaptation of phytoplankton to these environments. Compared to its coastal relative Thalassiosira pseudonana, the oceanic diatom Thalassiosira oceanica is highly tolerant to iron limitation. The adaptation to low-iron conditions in T. oceanica has been attributed to a decrease in the photosynthetic components that are rich in iron. Genomic information on T. oceanica may shed light on the genetic basis of the physiological differences between the two species. Results The complete 141790 bp sequence of the T. oceanica chloroplast genome [GenBank: GU323224], assembled from massively parallel pyrosequencing (454) shotgun reads, revealed that the petF gene encoding for ferredoxin, which is localized in the chloroplast genome in T. pseudonana and other diatoms, has been transferred to the nucleus in T. oceanica. The iron-sulfur protein ferredoxin, a key element of the chloroplast electron transport chain, can be replaced by the iron-free flavodoxin under iron-limited growth conditions thereby contributing to a reduction in the cellular iron requirements. From a comparison to the genomic context of the T. pseudonana petF gene, the T. oceanica ortholog can be traced back to its chloroplast origin. The coding potential of the T. oceanica chloroplast genome is comparable to that of T. pseudonana and Phaeodactylum tricornutum, though a novel expressed ORF appears in the genomic region that has been subjected to rearrangements linked to the petF gene transfer event. Conclusions The transfer of the petF from the cp to the nuclear genome in T. oceanica represents a major difference between the two closely related species. The ability of T. oceanica to tolerate iron limitation suggests that the transfer of petF from the chloroplast to the nuclear genome might have contributed to the ecological success of this species.

Description: Knowledge about the genetic connectivity of populations is crucial for conserving biological diversity at hydrothermal vents. However, despite the paucity of such data for deep-sea biota, vent communities become increasingly threatened by anthropogenic pressures through resource extraction. Deep-sea mussels of the genus Bathymodiolus are key species in hydrothermal ecosystems worldwide. Using transcriptome sequencing we investigate migration and gene flow patterns among 10 Bathymodiolus populations of the Mid-Atlantic Ridge (37°N to 9°S). We combine outputs of particle tracking analyses using a 1/20° ocean model with genotypic data derived from 103 molecular markers that were designed from high-throughput transcriptomes. Multilocus assignment and differentiation tests indicated the presence of one southern and two northern genetic pools that become increasingly isolated with geographic distance. In spite of the relatively long pelagic duration of Bathymodiolus veligers, our analyses also show that dispersal of more than 100 km is unlikely and that connectivity between known vent populations can only be achieved via intermediate stepping stone habitats. These results have important ramifications for biodiversity conservation in Mid-Atlantic vents that might become targets for mineral extraction activities.