Green Growth Inside Salamander Embryo Cells: A Surprising Biological Discovery

Scientists have confirmed that green algae live inside the cells of spotted salamander embryos, marking the first known case of a photosynthetic organism residing within vertebrate cells.

The discovery, reported by researchers from Dalhousie University and published in the Proceedings of the National Academy of Sciences, shows that the algae invade embryonic tissues and individual cells during development. This intracellular presence was observed in both the spaces between cells and within the cells themselves.

The algae, identified as a species closely associated with salamander eggs for over a century, were previously known to exist only in the jelly-like capsules surrounding the embryos. The new findings reveal that they penetrate the embryo’s tissue and establish a symbiotic relationship at the cellular level.

This form of symbiosis, where one organism lives inside the cells of another in a mutually beneficial arrangement, is termed endosymbiosis. While common in invertebrates and protists, it had never before been documented in a vertebrate host such as the spotted salamander (Ambystoma maculatum).

Researchers suggest the algae may be acquired from the environment and potentially transferred from adult salamanders to their offspring. Genetic traces of the algae have been detected in the reproductive tracts of some adults, indicating a possible intergenerational transmission mechanism.

The spotted salamander breeds in temporary ponds each spring, depositing eggs that develop over one to two months. The embryos, which later hatch into aquatic larvae with external gills, undergo metamorphosis over the following two to four months before transitioning to terrestrial life.

This discovery challenges long-held assumptions about the limitations of vertebrate immune systems, which were thought to prevent such intracellular invasions. The presence of photosynthetic algae within vertebrate cells opens new questions about metabolic exchange, immune tolerance, and evolutionary adaptation in complex organisms.

Further study is needed to determine whether the algae provide nutritional benefits to the developing embryo through photosynthesis, or if the relationship offers other advantages such as waste processing or oxygen production. The findings highlight the spotted salamander as a unique model for understanding how symbiotic relationships can evolve across broad biological divides.