Unveiling the Metabolic Strategies of Deep-Sea Coral-Associated Bacteria

A German-American research team, led by Dr. Samuel Vohsen from Lehigh University and Professor Dr. Iliana Baums from the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg, has discovered two unique bacterial species in the tissue of deep-sea corals from the Gulf of Mexico.

These newly identified coral symbionts have extremely small genomes, unable to produce energy from carbohydrates. The study, published in Nature Communications, highlights how few genes are required for these organisms to function. 

“This species is an impressive example of how few genes are needed for a functioning organism,” says Dr. Iliana Baums, Professor at the University of Oldenburg.

The team analyzed several colonies of two horn coral species, Callogorgia delta and Callogorgia americana, found at depths of 300–900 meters. During their investigations, they identified two closely related bacterial species from the class Mollicutes, which they propose to classify under a new family, Oceanoplasmataceae.

These bacteria reside in a gelatinous tissue layer of the corals, contributing to the immune system and nutrient transport. Thalassoplasma callogorgiae has 385 genes for protein-coding, while Oceanoplasma callogorgiae has only 359—significantly fewer than the roughly 21,000 genes in humans or the 4,000 in Escherichia coli. Lacking genes for carbohydrate metabolism, the bacteria rely solely on the amino acid arginine, sourced from their coral host, as an energy supply.

“It is astonishing that the bacteria survive on such little energy,” notes Baums. “They lack even the basic genes for carbohydrate metabolism—a trait universal among living creatures.”

The host coral may benefit from the bacteria’s unique capabilities. Genetic analysis reveals that the bacteria possess CRISPR/Cas systems, often used in biotechnology for gene editing, which may help the coral fend off infections. Additionally, the bacteria might metabolize arginine to provide nitrogen to their host.

Baums believes these symbionts offer new insights into coral ecology and adaptation as she studies the evolutionary history of these diverse organisms.

“It’s incredible that corals, despite their simple structure, can inhabit such a range of environments,” she says. “Their symbionts offer metabolic capabilities that the corals lack, helping them thrive under varied conditions.”

While tropical corals in shallow waters rely on algae for photosynthesis, deep-sea, cold-water corals likely depend on bacteria to convert nutrients and derive energy in the dark, nutrient-poor ocean depths.