Bhattacharya Lab Paulinella ovalis single cell genomics

Two cases of primary plastid endosymbiosis are known. The first occurred ca. 1.6 billion years ago and gave rise to the canonical plastid in algae and plants. The second is restricted to a genus of rhizarian amoebae that includes Paulinella chromatophora. Photosynthetic Paulinella species gained their plastid from a a-cyanobacterial source and are sister to plastid-lacking phagotrophs such as P. ovalis that ingest cyanobacteria. To study the role of feeding behavior in plastid origin, we analyzed single-cell genome assemblies from six P. ovalis-like cells isolated from Chesapeake Bay, USA. Dozens of contigs in these cell assemblies were derived from prey DNA of a-cyanobacterial origin and associated cyanophages. We found two examples of horizontal gene transfer (HGT) in P. ovalis-like nuclear DNA from cyanobacterial sources. This work provides the first evidence of a direct link between feeding behavior in wild-caught cells, HGT, and plastid primary endosymbiosis in the monophyletic Paulinella lineage.