Diatoms are some of the most common algae found in the ocean. There are at least 100,000 species.
Most of these tiny diatoms use photosynthesis. This means that they use sunlight, carbon dioxide and water to produce the sugar and energy they need to grow, live and reproduce.
However, some diatoms are different, such as the one with the not very catchy name of Nitzschia sing1.
"These algae have stopped photosynthesising and started living off kelp," explained Finn L. Aachmann, Professor at the Department of Biotechnology and Food Science at the Norwegian University of Science and Technology (NTNU).
He is part of a research group that has studied these aberrant diatoms. The senior author is Gregory Jedd at Temasek Life Sciences Laboratory in Singapore. Their research results have been published in PLOS Biology.
Breaking down kelp instead
"Unlike other diatoms, this and other related species break down kelp and get their carbohydrates from this source. In the past, we did not know why they did this, but now we do," said Aachmann.
The researchers studied the genes of the species called Nitzschia sing1.
"We found that the species has genes that allow them to make enzymes that break down alginate, a sugar found in the cell walls of brown algae," he said, calling the diatoms 'nature's own biorefinery'.
Enzymes are small molecular machines that accelerate chemical processes without being consumed themselves. The question, however, is why does this species and its close relatives have these useful genes?
Stole useful genes from bacteria
"The genes must originally have come from a marine bacterium. At some point in time, a predecessor of Nitzschia sing1 and the other species must have taken genes from the bacterium and incorporated them into their own genetic material, explained Aachmann.
These genes were then copied many times. Some of these copies mutated and contributed to new characteristics. Ultimately, Nitzschia sing1, and its close relatives that have descended from the original species, found they no longer needed their own photosynthesis. Instead, these species were able to obtain the building blocks they needed from kelp.
"This enabled this group of diatoms to inhabit a completely new ecological niche, where they live on kelp in tidal zones," said Aachmann.
So, why should this be of any interest to us?
New ways of using kelp?
The work means researchers now know more about how these algae get hold of the building blocks they need.
But it has also given us new insight into how one species can evolve into several species. In addition, it opens up opportunities to use the algae for the natural transformation of kelp.
Alginate is used in over 600 products that we humans use, from ice cream and gels in food to welding rods and bandages. The understanding gained from the diatoms can therefore have an impact on areas as diverse as the development of biofuels, proteins for feed, recycling, carbon cycle research, and directed evolution.
Not bad for research on a small, rule-breaking diatom.
The research was funded by Temasek, the Research Council of Norway and Deutsche Forschungsgemeinschaft.
References: Citation: Lim ZH, Zheng P, Quek C, Nowrousian M, Aachmann FL, Jedd G (2025) D iatom heterotrophy on brown algal polysaccharides emerged through horizontal gene transfer, gene duplication, and neofunctionalization . PLoS Biol 23(3): e3003038. https://doi.org/10.1371/journal.pbio.3003038
