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Diatoms Evolve New Dietary Habits by Adapting Bacterial Genes

Research reveals that certain diatom species from the Nitzschia genus have abandoned photosynthesis, opting instead to obtain carbon directly from their environment through a genetic adaptation acquired from a marine bacterium. This significant finding, led by Gregory Jedd and his colleagues at Temasek Life Sciences Laboratory in Singapore, was detailed in a recent publication in the open-access journal PLOS Biology.

Typically, diatoms are known for their ability to perform photosynthesis, converting sunlight into carbon compounds. However, some Nitzschia species have developed a distinct strategy, lacking chlorophyll and instead deriving carbohydrates from sources like seaweed and decomposed plants. The mechanisms behind this evolutionary shift have remained largely speculative until now, prompting researchers to sequence the genome of Nitzschia sing1 to uncover the details of this transition.

The genome analysis of N. sing1 revealed the presence of a gene responsible for encoding an enzyme that breaks down alginate—a carbon-rich polymer found in the cell walls of brown algae, including kelp. It appears that an ancestor of N. sing1 assimilated this gene from a marine bacterium long ago. Over generations, this gene underwent multiple duplications, acquiring various mutations that allowed the diatom to expand its functions. As a result, N. sing1 can now effectively break down alginate into usable carbon components, thus rendering photosynthesis unnecessary. This adaptation has facilitated the colonization of new ecological niches, particularly in intertidal zones where these diatoms can thrive on decaying seaweed.

Interestingly, while N. sing1 and its relatives have adapted to utilize alginate, other non-photosynthetic Nitzschia species do not share this capability. This observation implies that different Nitzschia species might exploit various methods to acquire carbon. The researchers advocate for further sampling of different Nitzschia species in natural environments and subsequent genomic analysis to enhance understanding of their carbon-gathering strategies. Such research could shed light on the diversification of species and the dynamics of carbon and nutrient cycling in coastal ecosystems.

The authors emphasize, “In this study, we demonstrate how a non-photosynthetic diatom evolved the ability to metabolize alginate, an abundant polysaccharide from brown algae. This research not only traces the evolutionary origins of this complex metabolic function but also reveals the genetic innovations that allowed these diatoms to adapt as obligate heterotrophs in new environmental contexts.”

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