Highly unusual bacteria discovered in deep-sea corals

There’s an eerie beauty and mystery in the dark depths of the Gulf of Mexico, where bacteria thrive alongside coral reefs.

These are not the colorful, sunlit corals we are most familiar with, but corals that flourish in the ocean’s abyss – devoid of sunlight – at depths ranging from 300 to 900 meters.

This mysterious underwater world is home to two soft coral species, Callogorgia delta and Callogorgia americana. Within the tissues of these corals, scientists recently discovered two peculiar bacterial species previously unknown to science.

Unique bacteria in coral tissues

The study was led by Professor Iliana Baums, a renowned scientist from the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB).

She collaborated with Dr. Samuel Vohsen from Lehigh University in the United States and other esteemed scientists from various institutions across the globe.

The research, published in the journal Nature Communications, creates a new frontier for marine biodiversity discoveries.

The unique bacterial species, found in the corals’ tissue layer that forms part of their immune defense system and transports nutrients, belong to the mollicutes class of bacteria.

Mollicutes are known to live as parasites either in or on the cells of plants, animals, and humans. In some cases, these bacteria cause diseases.

The scientists have proposed a new family for the two bacteria species called the Oceanoplasmataceae.

Extraordinary bacterial species

The existence of the newly discovered bacteria presents a puzzle – a mystery that scientists have yet to unravel.

“These species are impressive examples of how few genes are needed for a functional organism,” noted Professor Baums.

The Oceanoplasma callogorgiae contains only 359 genes that encode protein for metabolic functions, while the Thalassoplasma callogorgiae has 385 genes.

When compared with around 4,000 in the intestinal bacterium, Escherichia coli, and approximately 21,000 in humans, the difference is stark.

Bacteria’s energy source

The question that begs to be answered is, how can the metabolism of these microbes function with such a significantly reduced genome?

The answer is as astonishing as it is simple. Their energy source is not the typical carbohydrate metabolism found in most living organisms but the amino acid arginine.

The breakdown of arginine provides very little energy, leaving scientists confused about the bacteria’s survival.

Interdependent or parasitic relationship?

Uncertainty remains about whether the bacteria function solely as parasites or if there is a potential symbiotic relationship.

Genetic analysis revealed that these bacterial species use various defense mechanisms called CRISPR/Cas systems to get rid of foreign DNA. This process is also used to edit genes.

The bacteria could potentially be assisting the corals in fighting off pathogens. Alternatively, the host corals could be receiving nitrogen while the bacteria break down arginine.

The role of symbionts

“I always find it amazing that corals can colonize so many different habitats despite being very simple animals in terms of their genetic blueprint,” said Braum.

She noted that symbionts are crucial for the ability of corals to adapt to different environmental conditions. “They provide metabolic functions that the corals themselves lack.”

This discovery brings us one step closer to understanding the intricate and beautiful complexity of life that thrives in the obscure depths of our oceans.

Deep-sea bacteria and coral health

Beyond their unusual genomes and survival strategies, the bacteria raise intriguing questions about their potential roles in the deep-sea ecosystem.

While researchers have uncovered that the bacteria rely on the amino acid arginine for energy, they still do not fully understand how these microorganisms interact with their coral hosts in such extreme, nutrient-scarce environments.

One theory suggests that the bacteria might contribute essential nutrients or provide defense against other pathogens, potentially forming a mutually beneficial relationship with the corals.

Alternatively, they could act purely as parasites, exploiting their coral hosts’ resources to survive.

Future research directions

Further research aims to explore these possibilities, investigating whether this unique microbial partnership could shed light on how deep-sea corals endure environmental pressures – and possibly how they might adapt to changing ocean conditions.

This ongoing work emphasizes the intricate interdependencies in deep-sea ecosystems and highlights the resilience of life in Earth’s most extreme habitats.

Understanding these relationships could provide insights into the fundamental principles of symbiosis and survival in the ocean’s depths.

image Credit: ECOGIG Consortium, Creative Commons CC0 1.0

The study is published in the journal Nature Communications.

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