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The Functional Role of Fungi and Bacteria in Sulfur Cycling During Kelp (Ecklonia Radiata) Degradation: Unconventional Use of PiCrust2

Summary

When kelp washes up on beaches, microscopic fungi and bacteria work together to break it down and recycle its nutrients back into the ocean. This study shows that fungi play a much bigger role in this process than previously thought, especially in cycling sulfur compounds that affect climate. By understanding these microbial partnerships, scientists can better predict how coastal ecosystems respond to changes in seaweed production.

Background

Macroalgae contribute approximately 1521 ± 732 Tg C year⁻¹ to global net primary production, with fungal remineralisation of Ecklonia radiata detritus producing substantial amounts of climate-relevant compounds. While bacterial metabolic pathways in kelp degradation are well-characterized, fungal contributions remain underexplored due to lack of predictive tools equivalent to PiCrust2.

Objective

This study examined changes in fungal and bacterial communities during E. radiata degradation over 21 days in mesocosms, comparing microbial functional roles between blades and stipes. The researchers used next-generation sequencing and bioinformatics tools (FUNGuild, FungalTraits, and PiCrust2) to identify overlapping metabolic pathways between bacteria and fungi, particularly those related to sulfur cycling.

Results

Of 423 identified metabolic pathways, 342 have been documented in fungi, including 281 redox-related pathways, 220 NAD-associated pathways, and 194 sulfur metabolism pathways. Fungal communities shifted from endophytic (day 0, dominated by Aspergillus) to saprotrophic (day 21, dominated by Dothideomycetes and Sordariomycetes). The stipe supported greater metabolic complexity and fungal niche specialization compared to the blade.

Conclusion

Bacteria and fungi play complementary roles in kelp degradation with overlapping metabolic functions. Fungi are essential contributors to kelp remineralisation through NAD⁺-dependent and redox-related processes, particularly in sulfur cycling. These findings suggest fungi are not merely passive participants but key drivers of coastal biogeochemical cycles during macroalgal degradation.
  • Published in:Environmental Microbiology Reports,
  • Study Type:Experimental Study,
  • Source: PMID: 40708120, DOI: 10.1111/1758-2229.70140
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