Heliobacterium and the origin of chrysoplasts

Chrysoplasts, golden-yellow and brown photosynthetic membrane-bounded plastids, photosynthetic organelles of algae such as phaeophytes (brown seaweeds), bacillariophytes (diatoms) and chrysophytes (golden-yellow algae including silicoflagellates), are hypothesized to have originated from brownish photoheterotrophic bacteria such as the newly discovered anaerobic nitrogen-fixing Heliobacterium. The consequences of this hypothesis as well as the data required to verify or disprove it are presented.