Microbiology

The more (food) the merrier (polar marine fungi)

Reviewing:

Barone, G. et al. Local Environmental Conditions Promote High Turnover Diversity of Benthic Deep-Sea Fungi in the Ross Sea (Antarctica). J. Fungi 2022, Vol. 8, Page 65 8, 65 (2022). DOI: 10.3390/JOF8010065


When you think of fungi what do you think of? Maybe common varieties such as yeast and molds, or a dense forest floor with red and white-capped mushrooms. While all indeed fungi, these iconic examples represent only a small fraction of fungal diversity in the world with much left to be discovered. One biosphere where fungi are largely unexplored is the ocean. Yep, fungi are ubiquitous in the ocean! Researchers out of Italy show that fungi from Antarctic sediments are highly diverse and shaped by the environmental conditions they are found in.

Fun guys in disguise

Marine fungi, unlike mushroom, yeast, or mold that you are familiar with, spend most or all their time submerged in seawater. Although invisible to the naked eye, they are known to occupy a broad suite of habitats: within the sediment, on or inside other living animals, floating in the water, or encrusting hard substrates like rocks. These microscopic eukaryotes are found all over the ocean – from nearshore shallow estuaries to the deep seafloor. Marine fungi possess impressive abilities to break down hearty nutrients, eat and control parasites, and eliminate toxins (including oil and plastics!!!) from the environment. Their role as a decomposer is critical for sustaining ecosystem health by transferring energy and cycling nutrients up the food web to larger or more complex animals. Who knew fungi could be so wicked cool!

Even with such an important role in the ecosystem, marine fungi are poorly studied. There are currently 1,901 species of marine fungi, and scientists think this represents less than 1% of the total number of species to be discovered! The under-studied nature of marine fungi means that fungal communities in many marine habitats are not well understood. In the context of climate change, understanding fungal communities is critical to ensure healthy and balanced ecosystems. Polar regions are especially vulnerable to rapidly changing environmental conditions, and any ecological disturbances could lead to cascading effects throughout the ecosystem. To predict how this community might be impacted by climate change, scientists need to know where fungi occur, how their communities differ across oceans, and what factors dictate the composition of a fungal community. Italian researchers Dr. Barone and others sought to address these questions for two sites in Antarctica, a region rapidly undergoing climate change.

Image of petri dishes each containing a unique fungal strain collected exclusively from sponge hosts. Note the diversity of color and texture for even a subset of marine fungi. Image courtesy of Wikipedia.

Marine mushroom foraging, a.k.a sampling

Dr. Barone and colleagues collected sediment samples from Antarctica’s Ross Sea, the most productive stretch of the Southern Ocean — notable for being the least-iced and most-accessible coast of the continent. Samples were collected from two different sites, B and C – see map below, located 170 km apart, but housing different environmental properties. These sites vary in temperature, salinity, oxygen, sediment type, and detritus, which is indicative of how much food is available to the fungi to degrade. Once back in the lab, the scientists evaluated the fungal community by extracting DNA from their samples and sequencing it.

A) Map of the target sampling region for Dr. Barone et al.’s work in the Ross Sea off Antarctica’s coast. B) A zoomed-in view of the two sampling stations (B, and C). Figure courtesy of Barone et al. 2022

Big meals and big deals

Dr. Barone et al. found high levels of marine fungal diversity, 1,251 species in total, in sediments from Antarctica’s Ross Sea! Site B had much higher fungal abundances and more species than Site C. This site has greater amounts of detritus in the sediment and suggests that more available food can support both more individuals and species. Interestingly, the two sites only share 10% of species, which suggests that the different environmental conditions may also support specialized species in each site.

This work by Dr. Barone and fellow scientists provides new insights into the weird and wonderful world of marine fungi! They show that there are impressive and distinct fungi inhabiting the sediments of Antarctica’s Ross Sea. The community is strongly determined by the amount of detritus, or food, and to a lesser degree by other environmental conditions. This knowledge provides an important direction for future studies, including determining how marine fungi might be impacted by climate change.

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