Science & Technology

Hungry green algae prefer to eat bacteria alive

A green fluorescent image of the same algae as the brightfield image (left) of Pyramimonas parkeae. Bacteria ingested into cells have been identified (right). Credit: N. Bock & E. Kim

New studies point to potentially widespread phagocytosis among green algae and suggest improved methodologies in environmental microbiology.

According to new research, the ability of green algae to eat bacteria may be far more widespread than previously thought, and could be an important discovery for environmental and climate sciences. This work, led by a scientist at the American Museum of Natural History, Columbia University, And the University of Arizona have found that five strains of unicellular green algae consume bacteria only when they are alive, when they are “hungry.” This study is today, The ISME journal..

“Traditionally, we believe that green algae are pure photosynthetic organisms and produce food by soaking in sunlight,” said one of the corresponding authors of the study, a deputy curator at the American Museum of Natural History. Kim Eun-soo, a person, said. “But we have come to understand that there are potentially many species of green algae that can also eat bacteria when conditions are right. And we also see how much they eat as eaters. I found out if it was difficult. “

In 2013, Kim and her colleagues first provided conclusive evidence that green algae eat bacteria. This was indicated by the algae of the genus Symbomonas. While some in the field saw this behavior as a rare exception, Kim’s lab empowered itself using mixturetrophs, both photosynthesis and phagocytosis (cells eat). Algae continued to investigate whether other types of green algae (a term for the mode of feeding) are present. It’s hard to confirm until the research team comes up with a new experimental approach led by Nicholas Bock, a graduate student at Columbia University’s Lamont-Doherty Earth Observatory, and Sophie Charbet, a postdoctoral researcher at the museum. did.

Researchers have combined bacteria with five different strains of unicellular green algae called prassinophyceae for feeding experiments with live bacteria labeled with non-toxic fluorescent dyes and for analysis with a flow cytometer. It was. The flow cytometer measured the increase in green fluorescence levels of algal cells over time. This suggests that algae are consuming glowing bacteria. To confirm that ingestion is actually happening, researchers used a precision microscope to identify the origin of green fluorescence inside the algae cells. In the process, the team discovered two specific quirks about grumpy eaters. The algae strains tested ate only live bacteria (leaving the bacteria that died in the experiment) and ate more when the levels of other nutrients were low. These discoveries have a great impact on environmental research on green algae.

“Traditionally, when people study the intake of bacteria by marine algae for environmental samples, they use fluorescently labeled bacteria that have been killed in the labeling process,” Charvet said. “At least in the five algae strains we were culturing, they seem to preferentially eat live bacteria and scrape off killed bacteria, which algae feed to the bacterial community in the natural environment. This means that the impact can be significantly underestimated due to the method used. “

Green algae are found all over the world and help form the basis of aquatic food webs. Green algae, along with other photosynthetic organisms such as cyanobacteria, diatoms, and whirlpool algae (collectively referred to as phytoplankton), function as a type of biocarbon pump and are as large as trees in terrestrial ecosystems and other land plants. Consume carbon dioxide.

“For decades, scientists have been able to send satellites, obtain optical data, and infer the global distribution of phytoplankton through chlorophyll measurements,” said the University of Arizona, Tucson. Bock, who worked in Colombia under Solange Duhamel, said. “Through it, we have come to understand that phytoplankton is crucial to the carbon cycle. All this assumption is that all its chlorophylls simply represent photosynthesis. Easy to detect. The part of mixed phytoplank is not considered because there is no way [via satellite] If they are eating other cells. Our findings emphasize that the story is actually more complex. “

In parallel with an experiment led by Bock and Charvet, we investigated eating green algae bacteria using a gene-based predictive model created by John Burns of the American Museum of Natural History and the Bigelow Institute for Marine Science. .. The predictions were consistent with the experimental results, suggesting that the behavior was even more widespread among the trees of life of green algae.

Reference: Nicholas A. Bock, Sophie Charbet, John Barnes, Jantosho Galzen, Andrey Rosenberg, Solange Duamel, Uns Kim, “Experimental Identification and In Silico Prediction of Green Algae Bacteria”, 2021 March 2 ISME journal..
DOI: 10.1038 / s41396-021-00899-w

Other authors of this work include Yangtsho Gyaltshen of the American Museum of Natural History and Andrey Rozenberg of the Technion-Israel Institute of Technology.

This work is partially supported by the National Science Foundation numbers CAREER-1453639, OCE-14580950, and OCE-1458070, with the Simons Foundation grant number 382790.

Hungry green algae prefer to eat bacteria alive Hungry green algae prefer to eat bacteria alive

Back to top button