photosynthesis vs heterotrophy in diatoms – Science

Marine Diatoms Adapt to Seaweed Diet Thanks to Borrowed Bacterial Gene

Juliet Wilcox — Tue, 01 Apr 2025 18:04:11 +0000

A revolutionary discovery in evolutionary biology has just emerged from the coastal waters, illuminating the complex interplay between genes and dietary habits in diatoms, a diverse group of single-celled algae. Researchers from Temasek Life Sciences Laboratory, Singapore, have unearthed startling revelations about how some diatom species forsake the long-held practice of photosynthesis, a hallmark of their ancestral lineage, to embrace a heterotrophic lifestyle that allows them to harvest nutrients directly from their environment. This paradigm shift in metabolic strategy is believed to stem from an extraordinary event of genetic acquisition from marine bacteria, showcasing the remarkable adaptability of these organisms.

In a study published in PLOS Biology on April 1, the team detailed the genetic mechanisms that have facilitated this transition for members of the Nitzschia genus, particularly focusing on a species named Nitzschia sing1. The findings challenge conventional understanding of diatom ecology and evolution, which had long emphasized photosynthesis as the cornerstone of their survival and propagation. Instead, the revelation that certain diatoms have acquired the ability to directly consume carbohydrates from algal and plant materials presents a compelling narrative about the influence of environmental pressures and evolutionary adaptability.

Sequencing the genome of N. sing1 revealed a treasure trove of genetic information, including a notable gene coding for an enzyme capable of breaking down alginate, a carbohydrate polymer found in the cell walls of brown algae. This enzyme is pivotal for N. sing1’s new diet, as it allows the organism to convert the alginate into usable carbon units, effectively turning it into a carbon ‘hunter’ rather than a simple photosynthesizer. The gene’s origin is particularly fascinating—it is believed to have been absorbed from a marine bacterium, marking it as a prime example of horizontal gene transfer, a process where genetic material is exchanged between organisms in a manner other than traditional reproduction.

What makes N. sing1’s adaptation even more intriguing is the evolutionary pathway it seems to have taken following the initial gene acquisition. Researchers discovered that this gene underwent multiple duplications and accumulated mutations, each modification conferring new functions. This concept, known as neofunctionalization, is key to understanding how a single genetic innovation can lead to a plethora of new biological capabilities. Through this evolutionary lens, the journey of N. sing1 titillates the imagination, as it highlights not just the mechanisms of adaptation but the potential for future diversification among diatoms.

However, N. sing1 is not alone in the Nitzschia genus; there lie many other relatives that also inhabit various ecological niches. Some of these species are considered non-photosynthetic as well, yet they exhibit different approaches to carbon sourcing. This suggests a rich tapestry of evolutionary strategies at play among diatoms, waiting to be unraveled by subsequent genomic explorations. The researchers advocate for increased sampling and genomic analysis of diverse Nitzschia species, which could yield further insights into their respective metabolic strategies and adaptations.

The ecological implications of this research are vast. Understanding how these diatoms have evolved to exploit brown algae as a food source opens new avenues for exploring carbon cycling in coastal ecosystems. Since coastal waters are often zones of high biodiversity and productivity, understanding the role of heterotrophic diatoms within these habitats can shed light on nutrient dynamics, species interactions, and ecological stability. The capacity of diatoms like N. sing1 to thrive in intertidal zones by utilizing detritus broadens our comprehension of energy flow within these environments.

As we grapple with the consequences of climate change and habitat degradation, insights gained from studies like this can inform conservation efforts aimed at protecting coastal ecosystems. The adaptive strategies demonstrated by N. sing1 may also inspire biomimicry in engineering, biotechnology, and even sustainable resource management. Furthermore, examining gene transfer mechanisms may offer pivotal holds on advancements in genetic engineering and synthetic biology, connecting ecological discovery with practical applications.

The researchers’ findings not only trace evolutionary origins but also illuminate the inherent complexities embedded within metabolic capabilities. This intricate narrative enhances our understanding of diatoms, revealing their remarkable resilience and innovation in the face of environmental challenges. As further research unfolds, it may unveil even more surprises regarding their metabolic versatility and evolutionary potential, propelling diatoms into a new light within the scientific community.

In closing, the research published on the evolutionary capacity of Nitzschia sing1 stands as a testament to the power of interdisciplinary inquiry, merging molecular biology, evolutionary science, and ecology. It challenges us to rethink existing paradigms and embrace the intricacies of life on Earth. As we continue to explore the oceans and unravel the genetic secrets they house, we are compelled to reconsider our understanding of life’s adaptability amid shifting environmental landscapes.

This groundbreaking study promises to fuel further exploration into the realms of genetic evolution among microorganisms, with implications that resonate far beyond the shores where these organisms thrive. The journey from photosynthesis to heterotrophy encapsulates a profound story of survival, innovation, and evolutionary creativity, urging us to delve deeper into the mysteries of life that adapt to our ever-changing world.

Subject of Research: Nitzschia genus diatoms and genetic adaptations
Article Title: Diatom Heterotrophy on Brown Algal Polysaccharides Emerged Through Horizontal Gene Transfer, Gene Duplication, and Neofunctionalization
News Publication Date: April 1, 2025
Web References: DOI: 10.1371/journal.pbio.3003038
References: Lim ZH, Zheng P, Quek C, Nowrousian M, Aachmann FL, Jedd G (2025) PLOS Biology
Image Credits: Jedd Group (CC-BY 4.0)

Keywords: Nitzschia, diatoms, heterotrophy, evolution, horizontal gene transfer, alginate, carbon cycling, ecological adaptation.

Diatom surprise could rewrite the global carbon cycle

Violet Maxwell — Wed, 17 Jul 2024 18:15:46 +0000

When it comes to diatoms that live in the ocean, new research suggests that photosynthesis is not the only strategy for accumulating carbon. Instead, these single-celled plankton are also building biomass by feeding directly on organic carbon in wide swaths of the ocean. These new findings could lead researchers to reduce their estimate of how much carbon dioxide diatoms pull out of the air via photosynthesis, which in turn, could alter our understanding of the global carbon cycle, which is especially relevant given the changing climate.

This research is led by bioengineers, bioinformatics experts and other genomics researchers at the University of California San Diego. The new findings are published in Science Advances on July 17, 2024.

The team showed that the diatom Cylindrotheca closterium, which is found in oceans around the world, regularly performs a simultaneous mix of both photosynthesis and direct eating of carbon from organic sources such as plankton. In more than 70% of the water samples the researchers analyzed from oceans around the world, the team found signs of simultaneous photosynthesis and direct organic carbon consumption from Cylindrotheca closterium.

The team also showed that this diatom species can grow much faster when consuming organic carbon in addition to photosynthesis.

Furthermore, the new research hints at the tantalizing possibility that specific species of bacteria are feeding organic carbon directly to a large percentage of these diatoms living all across the global ocean.

This work is based on a genome-scale metabolic modeling approach that the team used to unravel the metabolism of the diatom Cylindrotheca closterium. The researchers constrained their genome-scale metabolic model with global gene expression data obtained from the TARA ocean expedition. The researchers believe this is the first time genome-scale models have been used at a global scale.

The team’s new metabolic modeling data support recent lab experiments suggesting that some diatoms may rely on strategies other than photosynthesis to intake the carbon they need to survive, thrive and build biomass.

The UC San Diego led team is in the process of expanding the scope of the project to determine how widespread this non-photosynthetic activity is among other diatom species.

Are ocean bacteria feeding diatoms?

When the team looked at the physical and chemical parameters measured in their ocean water samples – including temperature, pH, salinity, light, nitrogen and carbon availability – they did not find any correlation between those parameters and a tendency by the diatoms to steer away from photosynthesis-only strategies.

However, the team found a clear signal when exploring specific bacterial populations co-existing with the diatom Cylindrotheca closterium in the ocean water samples. This finding hints at bacteria-diatom interactions that drive the simultaneous mix of photosynthesis and direct consumption of organic carbon – a phenomenon known as “mixotrophy.”

The team believes that specific bacteria may be feeding the diatoms directly, helping these diatoms to be one of the most successful and important microbes on the planet, in terms of oxygen production, carbon sequestration, and as a foundation of food webs that support nearly all life in the ocean.

“Diatoms are major contributors to marine food chains and key drivers of the global carbon cycle. Previously, we have estimated all carbon cycling models on the assumption that the only role that diatoms play is in carbon dioxide fixation. Our findings demonstrate that this is not the case, but that diatoms simultaneously also eat organic carbon. In other words, we have shown that diatoms do not rely exclusively on carbon dioxide fixation for their growth and biomass production. We believe these results will have major implications for our understanding of global carbon cycling,” said UC San Diego Professor Karsten Zengler, professor in the Departments of Pediatrics and Bioengineering and researcher in the Center for Microbiome Innovation at the Jacobs School of Engineering.

“While there have been curious observations in the laboratory regarding diatoms deviating from photosynthesis, it has been impossible to test what kind of metabolism these diatoms perform in the ocean – until now. This is because there are many, many genes involved in this process, and it’s very difficult to delineate what process is active from gene expression data alone. Our approach gets around this challenge.”

The research team hopes this work will stimulate interest in taking a much closer look at our understanding of the global carbon cycle, taking into consideration this new broader understanding of how ocean diatoms get their carbon.

What the bacteria feeding the diatoms may be getting out of the relationship is another question for further research.

The paper “Mixotrophic growth of a ubiquitous marine diatom” by Kumar et al appears in Science Advances.

Complete author and funding information are listed in the paper.

The corresponding author is UC San Diego Professor Karsten Zengler. He holds faculty appointments in the Department of Pediatrics at the UC San Diego School of Medicine; and the Shu Chien-Gene Lay Department of Bioengineering at the UC San Diego Jacobs School of Engineering. He is a faculty member of the Center for Microbiome Innovation at the UC San Diego Jacobs School of Engineering and Affiliate Faculty in the Program in Materials Science and Engineering.

Journal

Science Advances

Method of Research

Data/statistical analysis

Subject of Research

Animals

Article Title

Mixotrophic growth of a ubiquitous marine diatom

Article Publication Date

17-Jul-2024

COI Statement

The authors declare no competing interests.