Strange Bacteria That Can’t Live Alone Hint at Early Steps to Complex Life

While all bacteria exist as single cells at some point in their lives, there is one remarkable exception: the multicellular magnetotactic bacteria (MMB).

A Window into Evolutionary History

Found in sulfide-rich sediments of a tidal salt marsh in Massachusetts, these MMBs are attracting the attention of scientists as they may offer clues about the evolutionary transition from simple, single-celled organisms to more complex, multicellular life forms like humans.

While other bacteria may form groupings from time to time, MMBs live exclusively together — to the point that they cannot survive if separated from their collective, a structure known as a consortium, which functions as a superorganism.

These consortia form a sphere with a hollow center, very similar to the shape of a blastocyst — the early stage in embryonic development that follows the fertilization of an egg by sperm.

The visual similarity to this developmental transition phase, where two cells with distinct genetic material form a unique and cohesive structure, makes this microorganism even more intriguing for evolutionary researchers.

However, unlike the blastocyst, each cell in an MMB consortium is an independent organism. This was already known, but scientists had assumed these cells were clones, as they synchronize to replicate when the entire consortium divides.

A study led by environmental microbiologist George Schaible from Montana State University analyzed the metagenomes of 22 MMB consortia and found that the cells are not identical. This genetic diversity allows different cells to play distinct roles within the group, functioning almost like organs in a body or members of a society, each with its specific duties.

MMBs utilize various carbon and energy sources, including transforming sulfate into hydrogen sulfide.

Autotrophic and Heterotrophic Growth

The data indicate that these bacteria can use both inorganic and organic carbon, suggesting they have autotrophic and heterotrophic growth modes. Additionally, different groups of MMBs show varying preferences for types of carbon.

This ability to use a variety of energy sources is believed to stem from the consortium’s internal diversity, which might explain why the cells are entirely dependent on each other for survival.

According to the researchers, the cells within a consortium exhibit dramatically different substrate uptake rates, indicating metabolic differentiation among them, as well as variations in protein synthesis activity.

Just as human communities survive through a division of labor — with different people responsible for various tasks — scientists believe that MMB consortia adopt a similar strategy: a “division of labor” in metabolism. The genetic and functional diversity found in the study strongly supports this theory.

The constant environmental changes of the tidal marsh where these bacteria live may have driven the evolution of this cooperation among genetically varied cells, allowing the consortium to better respond to natural challenges.

Cooperation Through Resource Sharing

The authors suggest that individual cells may metabolize specific substrates, such as acetate, and share these resources with other cells through the space between them, possibly using membrane vesicles.

They conclude that computational models could help better understand how these internal metabolic networks function, providing further support to the idea that this form of primitive life was already practicing something essential for complex organisms: specialized cooperation.

Read the original article on: Science Alert

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