Kelp-eating microalgae offer huge potential
Researchers have been studying algae that eat kelp instead of making their own sugar. The findings open up new ways of making all kinds of useful things out of kelp.
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 sunlight, carbon dioxide and water to produce the sugar and energy they need to grow, live and reproduce. This process is called photosynthesis.
From Sentosa Island in Singapore, where the diatoms are found along the coast. The inset shows laboratory-grown Nitzschia sing1 diatoms. Illustration: Jedd Group
However, some diatoms are different, such as the one with the not very catchy name of Nitzschia sing1.
“These algae have stopped photosynthesizing and started living off kelp,” explained Finn L. Aachmann, Professor at the Department of Biotechnology and Food Science at NTNU.
Aachmann is part of a research group that has studied these unusual diatoms. One of his colleagues is Gregory Jedd at Temasek Life Sciences Laboratory in Singapore. Their research results have been published in PLOS Biology.
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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?
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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,” Aachmann said.
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.
A summary of the genetic changes that caused Nitzschia sing1 diatoms to stop using sunlight and instead start living on organic matter. It also shows how this led them to evolve in many directions. Source: Jedd Group
But it has also provided new insight into how one species can evolve into several species. In addition, it opens the door on finding ways to use the algae for the natural transformation of kelp.
Alginate is used in over 600 products that 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) Diatom 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
