New Insight Into the Evolutionary Origins of Phylogenetic Interplay Between Sponges and Microbiome

Over the years, substantial evidence has consistently demonstrated the profound influence of the microbiome, encompassing all microorganisms residing within a living organism, on various vital processes and interactions with their hosts. Sponges, which hold a significant place among the oldest multicellular life forms on our planet, harbor a diverse range of microbial communities. Assistant Professor Sergio Vargas and Professor Gert Wörheide, hailing from the Department of Earth and Environmental Sciences and the GeoBio-Center of LMU, have spearheaded a recent study uncovering the molecular mechanisms through which sponges actively respond to changes in their microbiome, using the model organism Lendenfeldia chondrodes. These findings shed light on the deep evolutionary origins of the phylogenetic interplay between the host and its microbiome.

Sponges, possessing a simple structural organization, diverged from the rest of the animal kingdom over 600 million years ago during the course of evolution. Notably, sponges possess proteins responsible for regulating interactions between the sponge and its microbiome, enabling them to modify their morphology in response to microbiome changes. "This suggests that the sponge's ability to engage with the microbiome emerged early in evolution," explains Vargas. However, the molecular mechanisms underlying this phenomenon have yet to be extensively investigated. To address this, the researchers focused on the Lendenfeldia chondrodes sponge, a species commonly found in aquariums, and explored the extent to which alterations in the microbiome composition influence the gene activity within the sponge.

Defective microbiome triggers changes in the sponge

The sponge species Lendenfeldia chondrodes harbors a microbiome predominantly composed of photosynthetic cyanobacteria. While it primarily feeds by filtering microorganisms from the water, it also receives carbon compounds from its symbiotic partners. When the cyanobacteria are lost, such as due to shading, the sponges undergo significant morphological changes. In the study at hand, initially blue sponges with foliose growth forms transformed into white, thread-like morphotypes with distinct microanatomy.

By employing transcriptomic methods, the researchers were able to demonstrate, for the first time, that these morphological changes coincide with extensive modifications in gene regulation. "We observed alterations in gene activities associated with both immune response and development," highlights Vargas. This suggests that sponges possess the ability to perceive changes in their microbiome and actively respond to them through developmental processes. The researchers speculate that shaded sponges adjust their metabolism to compensate for the reduced supply of carbon compounds from their symbiotic partners. "Our findings emphasize the significance of the microbiome in the nutrition and development of animals in general, indicating a long shared evolutionary history between animals and their bacterial counterparts," concludes Vargas.