Triple Endosymbiosis Discovered (Biology)

The intracellular sulfur-purple bacterium “Candidatus Thiodictyon intracellulare” has lost the ability to oxidize sulfur and now supplies an eyelash animal with energy from photosynthesis / YouTube video available

A research team led by Dr. Sebastian Hess from the Institute of Zoology at the University of Cologne has discovered a very rare and puzzling triple endosymbiosis, which consists of an eyelash animal, a green alga and a previously unknown purple bacterium. As the researchers found out through genome analyzes of the pink-green ciliate, the bacteria involved belongs to the so-called sulfur-purple bacteria (family Chromatiaceae ), but has given up the otherwise typical oxidation of sulfur compounds. The genome of the purple bacterium is greatly reduced and suggests that the bacterium is now mainly in the service of carbon fixation and is no longer viable on its own. The new bacterial species “Candidatus Thiodictyon intracellulare” represents a remarkable exception among the previously known sulfur purple bacteria . The article“ A microbial eukaryote with a unique combination of purple bacteria and green algae as endosymbionts ”in the renowned journal Science Advances presents this new discovery and explains how the oxygen-sensitive purple bacterium lives together with green algae and ciliate animals.

The pink-green ciliate Pseudoblepharisma tenue lives in the low-oxygen sediments of the Simmelried, a moor system near Konstanz on Lake Constance. For a number of years now, with Dr. Hess hobby microscopist Dr. Martin Kreutz the occurrence of this unusual way of life. Since the eyelash animal cannot be reproduced in the laboratory to this day, a decision was made between Dr. Kreutz and the Cologne researchers developed a lively collaboration. The fresh sediment was always sent to Cologne by post. There, single cells of Pseudoblepharisma tenue were isolated from the samples and subjected to microscopic and genetic analyzes.

The study’s first author, Dr. Sergio Muñoz-Gómez was able to reconstruct the individual genomes of the three symbiotic partners and demonstrated the massive physiological reduction in purple bacteria. “An interesting picture emerges from the different perspectives, from observations of nature to the gene repertoire of the symbiotic partners. The symbiosis has created a hybrid creature that has never existed before: a mobile and voracious ciliate animal, which at the same time uses light energy in the deeper, oxygen-poor layers of the water ”, say the researchers. “The algae seem to play a subordinate role. Instead, the innovation comes from the oxygen-avoiding purple sulfur bacteria. “

Youtube video:

Featured image credit: Sebastian Hess


For publication:
https://advances.sciencemag.org/content/7/24/eabg4102


Provided by University of Cologne

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