Kyoto, Japan -- As tiny as they are, marine plankton play pivotal roles in biogeochemical cycles and in sustaining aquatic ecosystems, producing around half of the oxygen on Earth and also acting as carbon sinks. When they die, their decomposing cells produce dissolved organic carbon that can be transformed and stored in the ocean for thousands of years, so understanding plankton mortality is essential for uncovering the mechanisms behind marine ecosystems.
However, assessing the death of a particular plankton population out of a community consisting of hundreds of coexisting species poses a complex challenge. A team of researchers at Kyoto University addressed this by focusing on viral infection and cell lysis , the process through which a cell's membrane breaks down and releases its genetic information into the environment.
First, the team developed a method for measuring plankton lysis by growing cultures of two phytoplankton species, diatoms and raphidophytes , in a seawater-based medium, and then extracting rRNA and quantifying it using digital PCR . Since rRNA released into seawater degrades over time, the researchers added a culture of spike-in ribosomes to the medium and measured the degradation rate constant. The resulting flux model incorporated both changes in host cell-free rRNA and the degradation constant, making it possible to accurately assess the rate of cell lysis.
The results revealed that viral infection and subsequent cell lysis enhanced cell-free rRNA production rates by approximately 46-fold and 302-fold respectively, compared to the non-infected solution from which only very small amounts of rRNA were actively released.
In the diatom experiment, dissolved rRNA production peaked before the population density began to decline as a result of viral infection, indicating that active cell lysis was already underway while the population was still maintaining steady growth. From a biogeochemical perspective, this demonstrates that the supply of dissolved organic matter to the environment through cell death may actually occur during the growth phase rather than during apparent population decline.
"We did not expect the temporal decoupling between population declines and cell lysis," says corresponding author Hisashi Endo. "Observing the dynamics of living cells is not enough to evaluate the dissolved organic carbon that phytoplankton contribute to marine environments."
The methods for quantifying this "invisible death" of plankton provide valuable insights for accurately understanding material flows within ecosystems. Of course, reasons for plankton mortality are diverse and this study did not distinguish between different causes of cell lysis. In the future, the team intends to explore methods that will track the impacts and causes of cell lysis at the species level.
"Since we revealed that a wide variety of viruses are present in seawater, I have been interested in understanding their impact on the ecosystem," says Endo. "Using this research as a starting point, I hope to shed light on the true nature of the plankton ecosystem."
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The paper "Quantifying viral lysis in microalgae using cell-free rRNA" appeared on 10 September 2026 in MicrobiologyOpen , with doi: 10.1002/mbo3.70402
About Kyoto University
Kyoto University is one of Japan and Asia's premier research institutions, founded in 1897 and responsible for producing numerous Nobel laureates and winners of other prestigious international prizes. A broad curriculum across the arts and sciences at undergraduate and graduate levels complements several research centers, facilities, and offices around Japan and the world. For more information, please see: http://www.kyoto-u.ac.jp/en
MicrobiologyOpen
Experimental study
Cells
Quantifying viral lysis in microalgae using cell-free rRNA
9-Sep-2026
The authors declare no competing interests.