Primary Source: Hu, Jing, et al. “Natural algaecide sphingosines identified in hybrid straw decomposition driven by white‐rot fungi.” Advanced Science, vol. 10, no. 25, 2023, https://doi.org/10.1002/advs.202300569.
As climate change sets in, with each year seeming hotter than the last, very few people can deny the relief of cooling off in the ocean. However, even this simple pleasure is threatened by climate change, as ecological stressors can induce blooms of algae which produce toxic chemicals. This turns the sea into a field of poison, killing marine life and swimmers alike. While algal blooms are a natural process necessary to maintain the food chain of marine ecosystems, excessive algal blooms can increase competition for nutrient resources among algae, which in turn produce toxins in hopes of freeing up resources. Additionally, excessive algal blooms can block sunlight from reaching marine plants, preventing photosynthesis and the production of oxygen. This effect cascades and leaves ecological dead-zones, devoid of life long after the algal bloom has passed. While these harmful blooms have been an issue before, factors such as stress from climate change and excessive agricultural nutrients in wastewater have made this phenomenon an increasingly pressing concern for coastal communities. With that being the case, researchers have been considering various potential solutions to mitigate excess algal growth. One such group of researchers from Zhejiang University in China made progress in finding new, naturally produced algaecides up to ten times more effective than previous natural products.
White-Rot Fungi are the Right Rot Fungi
The introduction of agricultural straw, rich in various natural compounds found in plant and microbe immune systems, is a worldwide practice in algae prevention. It was famously discovered in 1980 when rotting hay was accidentally added to a British lake. With this practice as a baseline, the researchers sought to single out the compound(s) responsible for the decreased algal growth. To start, they tested the ability of varying kinds of agricultural straw. Whereas previous studies have focused mainly on barley straw, this study also considered wheat straw, maize straw, rice straw, and canola straw. By testing the algae inhibiting capabilities of these various straws, both on their own and when inoculated with white-rot fungi, fungi which can break down the structural compound lignin that gives many plants their woody rigidity, the researchers could determine whether the source of the anti-algal agent was from a particular species of plant, the process of decay in general, or a specific product of the decay of a particular plant species. Through this cross-referencing of species and preparations, the researchers found that white-rot infected straws inhibited algal growth long after being initially introduced, while the uninoculated straws without rot fungi were somewhat effective at inhibiting algal growth at first, but quickly declined after the first few days post-introduction. With this insight, the researchers cross-referenced genes present in different species of white-rot fungi that were activated specifically when infecting agricultural straw. They then tested the abilities of the compounds these genes encoded to perform various cellular processes necessary for inhibiting algal growth, such as the ability to metabolize photosynthesized carbohydrates and the structural protein lignin. Additionally, chemical analysis was done to group these compounds into different chemical families. Both of these actions served to shed light not only on which compound was responsible for the algal inhibition, but also potentially explain how the compound in question does so.
You Go Sphingosines!
The analysis of the many metabolic chemicals produced by white-rot fungi led to the discovery of a new family of organic chemicals called sphingosines. These chemicals were most significant in the inhibition of algal growth. Through analyzing the secretions of algal cells exposed to these chemicals, the researchers were able to get an idea of how these chemicals interfere with algal cells. They found that algae exposed to sphingosines had significantly lower photosynthetic ability, as well as significantly higher levels of antioxidants. These observations indicate that sphingosines likely prevent algal growth by both interfering with the cycle of photosynthesis and introducing reactive oxygen, which may bind to and negatively impact key cellular machinery within the algae. While the exact method is still unclear, sphingosines are still able to continually inhibit algal growth at levels significantly higher than other compounds of similar origin. Having a natural compound, easily degraded after use in nature, to handle harmful algal blooms both reduces the risk these blooms represent, while also not simply replacing them with the risk of synthetic compounds that may continue to pollute the marine ecosystem long after its intended use. Thorough research such as this helps to solve the world’s growing list of ecological issues in novel ways that don’t compromise between long-term effects and efficacy.