Green Microbes

01 October 2018 - By: Jonathan Smith

Green Microbes

Green Microbes


By Jonathan Smith

Traditional plant and animal biology were not the only focus in this year’s Annual Meeting. Microbial and algal organisms also received a lot of attention in the Green Microbes session, where speakers discussed the benefits of understanding their biology. This article features two key examples of research presented at the session: of coral symbiosis and of seaweed cell biology.

WORKING IN TANDEM

Coral reefs are diverse hotbeds of cooperative partnerships, one famous example being the iconic symbiosis between sea anemones and clownfish. Some of these cooperative relationships are crucial to the survival of the coral reef itself, as they provide scarce nutrients to the corals. “The clear blue tropical seas are very low in nutrients,” began session speaker Annika Guse, from the Centre for Organismal Studies, Germany. “Corals thus form symbiotic relationships with dinoflagellates, who reside inside the coral cells and whose photosynthesis provides nutrients for the host, and who receive shelter in exchange.” This process enables corals to produce immense structures like the Great Barrier Reef.

Given that this process is so important for tropical marine ecology, it is surprisingly under-studied. Why is this? Seeking to study more regarding the symbiotic bond, Annika explained: “Corals are very hard to rear for study in the lab; they famously breed just once per year and produce hard exoskeletons, making it all but impossible to use them in a lab every day”. Instead, researchers in this field employ a related organism that is easier to study: the marine sea anemone Aiptasia. “These organisms are easier to breed and use: they spawn once a month and thankfully have no hard exoskeletons,” Annika added. “Most importantly, they form symbiotic relationships that are very similar to those of corals.”

With a useful model species established, Annika’s group wants to know how the nutrients are passed from the symbiont to the host, as she explained: “These symbionts produce lots of lipids and sterols like cholesterol; our transcriptomic and proteomic work suggests that these sea anemones use Niemann-Pick type C (NPC2) proteins to bind and transfer these sterols from the symbiont to the host cell”. NPC2 proteins are notable because they are conserved across the animal kingdom, including in humans who have only one gene copy, compared to the multiple copies in the anemone genome. Furthermore, her group validated the model system by comparing these results with those from precious corals, and use mutant strains in order to confirm the functional role of these transport proteins.

With this knowledge, Annika’s group hopes to explore more of the symbiotic process in these animals. “It is fascinating because this process underpins the coral reef ecology,” concluded Annika. “Not only this, but they use proteins that are known in humans, and thus could teach us more about our own physiology and health.”

ALGAE BUILDING WALLS

Plant and algal cells have cell walls, a protective barrier that affects the morphology and durability of the plants. The cell wall is very important for the agricultural industry, as it controls when fruit becomes ripe, and affects the growth of plants for biofuels and more. Thus, understanding this structure is likely to be crucial for feeding and fuelling society in the future.

Structurally, the cell wall is not just a simple static barrier. Speaker John Bothwell from Durham University, UK, presented his work with this structure, explaining: “The plant cell wall is actually analogous to a car tyre; cellulose filaments give it tensile strength, while these filaments are held in shape by carbohydrate polymers, just like rubber holds steel filaments for tensile strength in the tyre.” Also, unlike other physical walls, this barrier is very dynamic, undergoing constant biochemical modifications such as sulphation and crosslinking.

John’s group wanted to understand how green seaweeds, a type of alga, modify their cell walls compared with land plants, a more closely-studied process. “Green seaweed is hugely important to study,” remarked John. “They are fundamental species in coastal ecology, useful for feed and biofuel production and, also, habitually weather immense tidal stresses that would kill any other plant species.” Thus, understanding how they modify their cell walls would reveal more about their hardiness and versatility.

To answer this question, John’s team went to the Durham coast and collected samples of green seaweed from the beach, before culturing them in bioreactors in the lab. To visualise the biochemical modifications, they used a special technique called solid-state nuclear resonance imaging (NMR). “Normally, carbohydrate modifications are very hard to measure because we need to hydrolyse them in acid or alkali, losing the modification in the process,” John explained. “With this solid-state NMR, however, we can measure it without hydrolysis, preserving the signal.”

John’s team discovered that these cell walls are rich in a modification called acetylation. “We also found that the samples alter their modifications in response to environmental stress; this will inform us a lot about coastal regions hit by climate change,” John enthused. These results also serve to visualise cell wall modifications in the context of the evolution of land plants, as John continued: “Green seaweed is an ancestor of modern land plants, thus we can understand how cell wall modifications changed, and gave rise to more complex morphologies.”

John aims to continue this research in both economical and ecological directions as he concludes: “This knowledge will help with the industrial farming of green seaweed for biofuels and feed, not to mention helping us to learn more regarding the central role of seaweed in coastal ecology.”

GOING GREEN

The talks at the session had a clear message: that algal and cell biology research remains hugely informative about ecology. Understanding the role of the smaller and less complex organisms in the ecosystem will therefore enable us to better preserve their habitats, and even use them more effectively in modern industry.

 

Category: Cell Biology
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Jonathan Smith

Jonathan Smith served as the SEB’s press intern for the annual meeting in summer 2016, and has since contributed articles for the SEB’s bulletin. After obtaining an undergraduate degree in Neuroscience from the University of Bristol, he is currently studying for a PhD in locust neurobiology in the University of Leicester and runs an active Twitter account communicating his work.

Twitter: https://twitter.com/j_ivories