Diatoms are a vast and diverse group of single-celled algae, classified as a type of phytoplankton, that exist across nearly all aquatic environments. These microorganisms are found in abundance in both freshwater and marine habitats, often suspended in the water column or adhering to surfaces. As a foundational component of the marine ecosystem, they represent a significant portion of Earth’s total biomass. They are one of the most common and ecologically important forms of microscopic life on the planet.
The Unique Architecture of the Diatom Shell
The defining feature of diatoms is their intricate external shell, known as a frustule, which encapsulates the entire cell. This protective casing is composed of hydrated silica, or biogenic glass, extracted from the surrounding water. The frustule is constructed with two overlapping halves, similar to a small pillbox, which provides a robust and rigid enclosure.
Each species possesses a distinct and highly ornamented frustule design, exhibiting complex patterns ordered on a nano-to-micrometer scale. This species-specific nanopatterning, including pores, ribs, and spines, provides structural support to the cell. The glassy composition and porous structure serve multiple functions, including physical protection from environmental stresses and predators. The arrangement of the pores is optimized to facilitate the exchange of nutrients and gases between the cell and the external environment.
Diatoms as Global Oxygen Producers
Diatoms occupy a foundational position as primary producers within the marine food web, converting light energy into chemical energy through photosynthesis. This process involves fixing carbon dioxide and releasing oxygen, making them immense contributors to the global oxygen supply. Estimates suggest that diatoms generate between 20 to 50 percent of all the oxygen produced on Earth each year, which is a contribution often compared to that of all the world’s rainforests combined.
Their photosynthetic activity is a major driver of the biological carbon pump, which transports carbon from the ocean’s surface to its deep interior. Diatoms draw large amounts of carbon dioxide from the atmosphere and surface waters, incorporating it into their biomass. When these organisms die, their heavy, silica-laden bodies sink rapidly to the ocean floor, effectively sequestering the carbon in deep-sea sediments. This downward flux of particulate organic carbon helps regulate the concentration of atmospheric carbon dioxide.
Diatoms have adapted specialized mechanisms to maximize their photosynthetic efficiency despite the low concentration of dissolved carbon dioxide in surface waters. They employ a CO2-concentrating mechanism (CCM) that utilizes the enzyme carbonic anhydrase to rapidly convert bicarbonate into CO2 at the cell surface. This allows them to utilize the large pool of inorganic carbon in seawater, supporting their rapid growth and massive annual blooms. Because of their size and silica composition, diatoms play a significant role in exporting this carbon to the deep ocean.
How Diatoms Reproduce
The life cycle of diatoms is primarily dominated by asexual reproduction, which occurs through a process called binary fission, allowing for rapid population growth under favorable conditions. During this division, the two halves of the silica frustule separate, and each daughter cell receives one of the parent’s shell halves. The larger half is called the epitheca, and the smaller half is the hypotheca.
Each newly formed cell then synthesizes a new, smaller hypotheca within the inherited valve. This mechanism results in a unique challenge for the population, as the daughter cell that receives the smaller half of the original frustule will inevitably be slightly reduced in size. Through successive generations of asexual division, the average cell size of the diatom population gradually decreases.
When an individual diatom reaches a minimum size threshold, typically about one-third of its maximum size, it is prompted to switch to sexual reproduction. This process involves meiosis to produce gametes that fuse to form a zygote. The resulting zygote sheds its silica shell and expands into a large, non-silicified structure called an auxospore. The auxospore grows to the maximum size characteristic of the species before developing a new, full-sized frustule, thereby restoring the size of the lineage and beginning the cycle anew.
Commercial and Scientific Uses
The robust, highly patterned silica shells of diatoms have led to various human applications, both historical and modern. Diatomaceous Earth (DE) is the most common commercial product, consisting of vast, soft deposits of fossilized frustules that have accumulated over millions of years. This fine, powdery material, with particle sizes generally ranging from 10 to 200 micrometers, is used extensively in industry.
Uses of Diatomaceous Earth and Diatom Structures
It is an effective filtration agent for liquids, including water and beverages.
Its fine, abrasive texture makes it suitable for use as a mild abrasive in metal polishes and toothpaste.
The complex micro- and nanostructures are being studied for advanced applications in nanotechnology, such as templates for biosensors and drug delivery systems.
The unique patterns of diatom species can be used in forensic science to help determine if a victim drowned and identify the specific body of water involved.