{"id":387402,"date":"2026-07-06T00:06:29","date_gmt":"2026-07-06T00:06:29","guid":{"rendered":"https:\/\/www.newsbeep.com\/us-ca\/387402\/"},"modified":"2026-07-06T00:06:29","modified_gmt":"2026-07-06T00:06:29","slug":"scientists-discover-how-algae-colonized-corals-a-symbiosis-that-fueled-the-growth-of-the-worlds-reefs","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us-ca\/387402\/","title":{"rendered":"Scientists discover how algae colonized corals \u2014 a symbiosis that fueled the growth of the world\u2019s reefs"},"content":{"rendered":"

The reefs scattered throughout the tropics arose only after algae took up full-time residence in coral cells, supplying corals with abundant food and enabling them to build extensive shallow-water communities. But with warming oceans, algae are often abandoning coral \u2014 causing what\u2019s known as bleaching \u2014 and turning reefs that were once teeming with life into ghost towns.<\/p>\n

A research team at UC Berkeley has now answered a major question in coral biology: How are algae able to thrive inside the cells of coral? The finding could lead to new insights into why algae and coral are failing to thrive symbiotically and suggest ways to reestablish the connection and save the world\u2019s reefs.<\/p>\n

The conclusions come from experiments conducted in the lab of Phillip Cleves<\/a>, a Berkeley assistant professor of molecular and cell biology who has constructed a state-of-the-art saltwater nursery for coral. On Australia\u2019s Great Barrier Reef, corals spawn once a year, releasing eggs and sperm in great clouds on a night in October or November around the full moon. This makes it hard to conduct genetic studies to understand the symbiotic relationship between algae and corals and their response to heat stress.<\/p>\n

In their nursery, Cleves and his team have been able to raise different groups of corals to spawn throughout the year, giving researchers the opportunity to conduct genetic experiments every few months.<\/p>\n

\"aCorals from the species Galaxea fascicularis, native to the Great Barrier Reef, growing in a saltwater aquarium at UC Berkeley. The smaller coral, held by Ty Engelke, was born and raised in captivity. On the reef, coral spawn at midnight in November during the full moon. In this one-of-a-kind lab, researchers manipulate light and heat to simulate spawning conditions and jet-lag some of the corals so that they spawn at different times of year, providing more opportunities for genetic manipulation. <\/p>\n

Brandon Sanchez Mejia for UC Berkeley<\/p>\n

Based on genetic manipulations of these lab-grown corals and related anemones, which also incorporate algae into their cells, the researchers are challenging the assumption that coral long ago absorbed algae into specialized compartments inside their cells called symbiosomes. Symbiosomes resemble mitochondria, the powerhouses of the cell, and chloroplasts, which harbor the photosynthetic machinery in plants. Both are thought to have been independent organisms that were long ago incorporated into cells and are now essential cellular components in all animals, plants and fungi.<\/p>\n

Cleves argues instead that algae parasitized coral, having found a way to live unscathed inside a type of lysosome, the cellular organs that normally digest food and invading organisms. In doing so, the algae learned how to absorb carbon from the host cell and release the products of photosynthesis \u2014 primarily glucose \u2014 to feed the coral. That\u2019s a win-win for both algae and coral, and for other animals that harbor symbiotic algae.<\/p>\n

In a paper to be published online<\/a> July 1 in the journal Cell, Cleves and his colleagues report experiments that support this idea that symbiosomes form by fusing with lysosomes, and that algae have somehow evolved to resist the active digestive enzymes in the lysosome.<\/p>\n

I think about it as an everlasting gobstopper.<\/p>\n

Phillip Cleves, UC Berkeley assistant professor of molecular and cell biology<\/p>\n

\u201cParasites basically trick cells to do what they want. That\u2019s what I think is happening here,\u201d Cleves said. \u201cThe algae are hijacking the nutrient centers of the cells and acting like food that just never gets digested because they can fix carbon and make glucose from photosynthesis. I think about it as an everlasting gobstopper.\u201d<\/p>\n

He noted that the difference is not always clear between a parasite, which exploits its host without the host benefitting, and a symbiont, which lives mutualistically with its host. The coral-algae relationship could be a new type of symbiosis that involves parasitizing a cellular organelle.<\/p>\n

\u201cIt\u2019s good for the coral, it\u2019s good for the algae, so it\u2019s symbiosis,\u201d he said. \u201cBut I think it\u2019s basically repurposing the entire cell and taking over that nutrient center.\u201d<\/p>\n

Promiscuous algae<\/p>\n

In genetic experiments led by postdoctoral fellow Shumpei Maruyama<\/a> of Berkeley and doctoral student Catherine Henderson of Carnegie Science in Baltimore, Cleves and his colleagues identified at least 200 proteins located on the symbiosome in which algae live. One of the proteins transports bicarbonate, which is converted to carbon dioxide in the symbiosome, potentially explaining how the alga gets the carbon dioxide it needs to convert sunlight into sugars, despite being isolated inside a cell inside the stomach of the coral.<\/p>\n

\"lightA half-inch-long anemone, Aiptasia, in a saltwater tank at UC Berkeley. The animals are used in genetic experiments to discover how algae form symbiotic relationships with a range of animals, from corals and anemones to jellyfish.<\/p>\n

Brandon Sanchez Mejia for UC Berkeley<\/p>\n

\u201cBy doing a CRISPR knockout in the coral Galaxea fascicularis, we\u2019ve shown that this bicarbonate transporter is required for symbiosis,\u201d Maruyama said.<\/p>\n

Cleves is currently investigating the role played by the other symbiosomal proteins in hopes of identifying how heat stress disrupts this amicable living situation, causing coral to lose their algae. He\u2019s also exploring how these proteins are involved in communication between the algae inside the symbiosome and the coral cell.<\/p>\n

\u201cOur overall research goal is to understand symbiosis and also to understand the genetic mechanisms for why corals bleach,\u201d he said. \u201cWe are now showing that the symbiosome is actually a type of phagolysosome, which is profound. We think that this hijacking of the phagolysosome tells us how these algae are so promiscuous at evolving new symbioses with coral, anemones, jellyfish, clams and even flatworms.\u201d<\/p>\n

A coral nursery<\/p>\n

In the basement of Berkeley\u2019s Koshland Hall, Cleves proudly showed off the one-of-a-kind coral nursery that he and lab manager Natalie Swinhoe designed down to the last pipe. Online since January, when Cleves arrived on campus, it consists of osmotic filters that purify city drinking water that is then mixed in three large vats with evaporated salt from the Red Sea. This reconstituted seawater is then piped into brightly-lit trays of coral \u2014 Galaxea fascicularis, a reef-building species from the Pacific Ocean \u2014 and smaller basins housing Aiptasia, small anemones. The lab is the only one on campus with seawater on tap.<\/p>\n

\"aPhillip Cleves, assistant professor of molecular and cell biology, standing next to one of the saltwater aquaria in which he raises coral that spawn throughout the year.<\/p>\n

Brandon Sanchez Mejia for UC Berkeley<\/p>\n

Following years of experimentation, including during the past five years at Carnegie Science, Cleves perfected a technique for getting coral populations in his lab to spawn throughout the year. Because they spawn only once a year in their native reefs, he originally had to travel to Australia for once-a-year genetic experiments on coral. After other researchers learned how to raise coral in the lab, Cleves decided to establish his own lab nursery. Through experimentation, he discovered that, by slowly altering the light cycle and temperature, he could get corals to shift their yearly spawning cycle. Over a two-year period, the corals thoroughly adjust to this jetlag. His Berkeley lab now has six different tanks of coral that should spawn sequentially, providing six opportunities each year to conduct genetic experiments on coral eggs.<\/p>\n

\u201cOur big advance here is that we\u2019re coupling the technology to spawn the animals with our ability to genetically engineer them,\u201d he said. \u201cIt really allows us to study gene function for the first time, to study coral-algal symbiosis, bleaching and heat tolerance. We have developed a variety of genetic tools: we can do CRISPR, we can do plasmid transgenesis, we can do RNAi knockdown. The paper is the first time we\u2019re showcasing the powerful insights that can be made with these new technologies.\u201d<\/p>\n

While spawning every few months is frequent enough to let him test ideas on his lab corals, Cleves\u2019 everyday experimental model is Aiptasia, which spawns every week and like many cnidarians \u2014 the group that includes jellyfish, corals and anemones \u2014 also sequesters algae.<\/p>\n

Membrane trafficking<\/p>\n

The researchers first isolated the symbiosome membrane in Aiptasia and identified the number and types of proteins in it. They discovered that there are about 200 proteins, many of them also found in the lysosome of the anemone. By knocking down some of these proteins using RNA interference (RNAi), Cleves and his colleagues showed that many of the lysosomal proteins in the symbiosome are required for algae to live inside these organelles. Among these are proteins that shuttle molecules in and out of the symbiosome and degrade other proteins.<\/p>\n

\"threePhillip Cleves (center), postdoctoral fellow Shumpei Maruyama (right) and research technician Ty Engelke pose between ranks of saltwater tanks containing anemones, Aiptasia.<\/p>\n

Brandon Sanchez Mejia for UC Berkeley<\/p>\n

\u201cThere are several vesicle trafficking proteins that we think are actually how the animal and the algae communicate, because they are trafficking cargo on and off the symbiosome, bringing stuff to the algae,\u201d Cleves said. \u201cWe found a huge diversity of transporters that are predicted to transport everything from lipids to ammonium to neurotransmitters to histidine, as well as bicarbonate. And the most paradoxical thing of all was that we found a huge diversity of lysosomal proteases \u2014 these proteins usually eat up the contents of the lysosome to scavenge food to fuel the (coral) cell.\u201d<\/p>\n

The two lead authors subsequently used CRISPR to mutate the bicarbonate transporter in coral and found that this interfered with algal symbiosis, demonstrating its importance in supplying coral algae with carbon.<\/p>\n

To Cleves, the ability of one group of algae \u2014 dinoflagellates that are now grouped into a single family of symbionts, Symbiodiniaceae \u2014 to survive inside the stomachs of cells explains their success in colonizing a broad range of marine creatures. Because lysosomes are cellular compartments found in all animals and conserved through evolution, the symbiont should be able to hijack these compartments in many hosts to evolve new symbioses.<\/p>\n

\u201cIf evolving a new symbiosis is as simple as resisting lysosomal digestion, we should be able to have the algae persist inside lysosomes in other organisms, because much of the machinery is conserved,\u201d he said.<\/p>\n

While this work sheds light on how corals and algae work together during good times, it may also tell biologists something about coral bleaching.<\/p>\n

\u201cWe think dysfunction of the symbiosomal proteins might be related to the breakdown of symbiosis, so we\u2019re now analyzing how the proteome shifts during heat stress to try to understand how this organelle changes during bleaching,\u201d Cleves said.<\/p>\n

Cleves is supported by the Gordon and Betty Moore Foundation (12187), National Science Foundation (2128073), a Revive and Restore Grant (2023-069) and a Pew Biomedical and Marine Fellow Award (00036631). Other co-authors of the paper are Swinhoe, Emily Meier and Ty Engelke of Berkeley and Griffin Kowalewski of Carnegie Science.<\/p>\n","protected":false},"excerpt":{"rendered":"The reefs scattered throughout the tropics arose only after algae took up full-time residence in coral cells, supplying…\n","protected":false},"author":2,"featured_media":387403,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[34],"tags":[12455,107616,103017,143,145,144,8939],"class_list":["post-387402","post","type-post","status-publish","format-standard","has-post-thumbnail","category-oakland","tag-biology","tag-crispr","tag-evolution","tag-oakland","tag-oakland-headlines","tag-oakland-news","tag-press-releases"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts\/387402","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/comments?post=387402"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts\/387402\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/media\/387403"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/media?parent=387402"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/categories?post=387402"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/tags?post=387402"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}