Study Sheds Light Into How Green Algae Engulfed Bacteria Billions Of Years Ago
A new study offers a glimpse at how early organisms dating back more than one billion years may have acquired free-living photosynthetic cells.
AsianScientist (May 27, 2013) - A team of researchers has captured images of green alga consuming bacteria, offering a glimpse at how early organisms dating back more than one billion years may have acquired free-living photosynthetic cells.
This acquisition is thought to have been a critical first step in the evolution of photosynthetic algae and land plants, which, in turn, contributed to the increase in oxygen levels in Earth's atmosphere and ocean and provided one of the conditions necessary for animal evolution.
In the study published in Current Biology, researchers identify a mechanism by which a green alga that resembles early ancestors of the group engulfs bacteria, providing conclusive evidence for a process that had been proposed but not definitely shown.
"This behavior had previously been suggested but we had not had clear microscopic evidence until this study," said Eunsoo Kim, assistant curator in the Museum's Division of Invertebrate Zoology and corresponding author on the paper. "These results offer important clues to an evolutionary event that fundamentally changed the trajectory of the evolution of not just photosynthetic algae and land plants, but also animals."
In green algae and land plants, photosynthesis, or the conversion of light into food, is carried out by a specialized cell structure known as a chloroplast. The origin of chloroplast is linked to endosymbiosis, a process in which a single-celled eukaryote - an organism whose cells contain a nucleus - captures a free-living photosynthetic cyanobacterium but does not digest it, allowing the photosynthetic cell to eventually evolve into a chloroplast. The specific feeding mechanisms for this process, however, have remained largely unknown until now.
In this study, researchers used transmission electron microscopy (TEM) and feeding and staining experiments to take conclusive images showing how a basic green alga from the genus Cymbomonas feeds on bacteria.
The alga draws bacterial cells into a tubular duct through a mouth-like opening and then transports these food particles into a large, acidic vacuole where digestion takes place. These photosynthetic modern alga are believed to have descended from colorless ancestors of green algae and land plants and may have played important roles in the evolution of early photosynthetic eukaryotes, the precursors to plants like trees and shrubs that cover the Earth today.
The article can be found at: Maruyama S et al. (2013) A Modern Descendant of Early Green Algal Phagotrophs.
Source: American Museum of Natural History.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.