Scientists unravel the mystery of Paulinella, an ancient amoeba that consumed a bacterium to become photosynthetic

paulinella-chromatophora

As part of a new research, an international team of scientists has attempted to solve the mystery surrounding Paulinella, a tiny amoeba that consumed a photosynthetic bacterium some 100 million years ago, keeping it alive to produce food through photosynthesis. The robbery allowed the ancient amoeba to exploit the bacterium’s genes for photosynthesis, something that it had previously lost due to evolution. Speaking about the study, Debashish Bhattacharya, a professor at Rutgers’ Department of Ecology, Evolution and Natural Resources and the paper’s co-author, said:

The major finding of the study is the microbial world, which we know is full of valuable genes, can move these genes between organisms according to need. When a microbe has a gene deficit, it can in some cases fill that deficit by grabbing the same gene from the environment. This shows how fluid microbial genomes really are.

Recently published in the Proceedings of the National Academy of Sciences journal, the research was conducted by a joint team of German and American scientists. Photosynthesis, as most know, is the process by which plants and alga, containing the green pigment chlorophyll, use sun’s energy to convert water and carbon dioxide into sugar and oxygen. The origin of photosynthesis, researchers believe, can be traced back to a similar ancient theft. Dana C. Price, a professor at the university’s School of Environment and Biological Sciences, said:

But people should not get the idea that humans will be grabbing bacterial genes any time soon, because they have a sequestered (protected) germ line. This is about microbial life such as bacteria and single-celled eukaryotes.

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Approximately 1.5 billion years ago, an algal predecessor swallowed a photosynthetic bacterium whole, reducing it to a chlorophyll-containing plastid known as chloroplast. Present in the cytoplasm of plant cells, plastids are a set of organelles that in turn carry the DNA material. This engulfing process, as pointed out by the scientists, is referred to as primary endosymbiosis, and is largely responsible for the appearance of plant-eating animals on Earth.

Scientific studies pertaining to endosymbiosis dates back to 1895, when German naturalist Robert Lauterborn composed a paper on Paulinella chromatophora. Credited with its discovery, Lauterborn wrote that the amoeba contains two sausage-shaped elongated plastids, called chromatophores, that facilitate the process of photosynthesis. This, according to Lauterborn, could point towards a symbiosis between two cells.

For many years after that, researchers failed to locate Paulinella cells in the environment. Around 20 years back, German scientist Michael Melkonian was able to acquire a sample of the elusive organism, culturing it in a lab in Cologne. Recently, a team led by Eva Nowack conducted a thorough analysis of the ancient amoeba, unraveling the rules and mechanisms of genome evolution that eventually made way for photosynthesis.

It is a well-known fact that cells residing in other cells undergo mutations that alter its DNA material, turning it into something completely different from the genome of its own species. This process, which is known as Muller’s ratchet, contradicts the very basis of endosymbiosis. Bhattacharya explained:

Evolution can find a way, in this case by solving the problem of broken genes by gathering replacement genes from the environment. Who knows, in a 100 million years or so, the descendants of Paulinella might become the dominant plants on our planet… It’s really remarkable that a paper written in a journal 120 years ago actually laid the foundation for this study. It’s very rare that a species that is so hard to find and culture starts to play an important role in understanding fundamental processes in cells.

Source: Rutgers University

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