Are heterotrophic and silica-rich eukaryotic microbes an important part of the lichen symbiosis?

Abstract

We speculate that heterotrophic and/or silica-rich eukaryotic microorganisms maybe an important part of the lichen symbiosis. None of the very few studies of heterotrophic protists associated with lichens have considered the possibility that they may be of functional significance in the lichen symbiosis. Here we start to develop, currently speculative, theoretical ideas about their potential significance. For example, all the protist taxa identified in lichens we sampled in Ohio USA depend on silica for growth and construction of their cell walls, this could suggest that silica-rich lichen symbionts may be significant in the biogeochemistry of the lichen symbiosis. We also present arguments suggesting a role for protists in nitrogen cycling within lichen thalli and a potential role in controlling bacterial populations associated with lichens. In this necessarily speculative paper we highlight areas for future research and how newer technologies may be useful for understanding the full suite of organisms involved in the lichen symbiosis.

Why is the world green? The interactions of top–down and bottom–up processes in terrestrial vegetation ecology

“…Presumably bottom-up processes such as the innate immune system of plants (Jones and Dangl 2006) play a major role in this. On occasions, top-down process may also have a role -for example one of us has recently speculated that heterotrophic protists may play a role in keeping bacterial populations in lichens under control (Wilkinson et al 2015). The role of microbial processes in each of these contexts is understudied, and we may find out a lot more over the next few decades.…”

Lichens redefined as complex ecosystems

“…We now know that the primary photobiont need not be restricted to a single strain of algae, but rather a co-existence of multiple strains may contribute to the resilience of lichens (Casano et al, 2011). Meanwhile protists, and even viruses, of lichens have been discovered in association with lichens (Wilkinson et al, 2015;Petrzik et al, 2019). As pointed out by Farrar (1976), lichens seem to have evolved as open systems, sometimes with special structures to facilitate gaseous exchanges, and can be interpreted as miniature ecosystems including a variety of organisms operating at different trophic levels.…”

Saccharomycomorphapsychra n. g., n. sp., a Novel Member of Glissmonadida (Cercozoa) Isolated from Arctic and Antarctica

“…Indeed, lichens seem to be an open and miniature ecosystem with a variety of organisms (Hawksworth and Grube 2020). Protists isolated from lichens had been reported sporadically, and what is currently known is likely the tip of an iceberg of diversity (Anderson 2014;Roberts and Zimmer 1990;Wilkinson et al 2015). The ecological roles of protists in lichens are far from clearly illuminated, and some indirect evidence shows that the protists might take part in the nutrient cycle in soils and lichen thalli (Ellis et al 2005;Wilkinson and Mitchell 2010).…”

“…The ecological roles of protists in lichens are far from clearly illuminated, and some indirect evidence shows that the protists might take part in the nutrient cycle in soils and lichen thalli (Ellis et al 2005;Wilkinson and Mitchell 2010). Protists may also play a potential role in influencing bacterial populations associated with lichen thalli (Wilkinson et al 2015). Research on protists related to mosses was primarily focused on their ecology (Anderson 2000;Anderson 2006), and two protists (Spumochlamys perforata, Spumochlamys bryora) were isolated from mosses in recent years (Kudryavtsev et al 2009).…”