Abstract
Lichens and their isolated symbionts are potentially valuable resources for biotechnological approaches. Especially mycobiont cultures that produce secondary lichen products are receiving increasing attention, but lichen mycobionts are notoriously slow-growing organisms. Sufficient biomass production often represents a limiting factor for scientific and biotechnological investigations, requiring improvement of existing culturing techniques as well as methods for non-invasive assessment of growth. Here, the effects of pH and the supplement of growth media with either D-glucose or three different sugar alcohols that commonly occur in lichens, D-arabitol, D-mannitol and ribitol, on the growth of the axenically cultured mycobiont isolated from the lichen Xanthoria parietina were tested. Either D-glucose or different sugar alcohols were offered to the fungus at different concentrations, and cumulative growth and growth rates were assessed using two-dimensional image analysis over a period of 8 weeks. The mycobiont grew at a pH range from 4.0 to 7.0, whereas no growth was observed at higher pH values. Varying the carbon source in Lilly-Barnett medium (LBM) by replacing 1% D-glucose used in the originally described LBM by either 1%, 2% or 3% of D-mannitol, or 3% of D-glucose increased fungal biomass production by up to 26%, with an exponential growth phase between 2 and 6 weeks after inoculation. In summary, we present protocols for enhanced culture conditions and non-invasive assessment of growth of axenically cultured lichen mycobionts using image analysis, which may be useful for scientific and biotechnological approaches requiring cultured lichen mycobionts.
Highlights
Lichens represent one of the most successful symbiotic associations on Earth and are capable of surviving in extreme environments (Kranner et al 2008; Grube 2010; Meeßen et al 2013a, 2013b), where life faces its limits
Mycobiont cultures grown on Lilly-Barnett medium (LBM) supplemented with 3% of either D-arabitol, D-glucose, D-mannitol or ribitol instead of 1% D-glucose were photographed every second week for up to 8 weeks
Secondary lichen metabolites primarily produced by mycobionts, such as the anthraquinone parietin, parietinic acid, emodin, fallacinal or teloschistin produced by X. parietina, receive increasing attention due to their potential medicinal properties (Boustie and Grube 2005; Basile et al 2015; Łaska et al 2016)
Summary
Lichens represent one of the most successful symbiotic associations on Earth and are capable of surviving in extreme environments (Kranner et al 2008; Grube 2010; Meeßen et al 2013a, 2013b), where life faces its limits (de Vera et al 2008; de la Torre et al 2010). The fungal partner, which gives the name to the lichen, is responsible for building the complex structure of the lichen thallus, it can only achieve this in symbiosis with a compatible photobiont (Honegger 1993; Kranner et al 2005; Meeßen et al 2013a). Lichen mycobionts produce a plethora of secondary fungal products with antibiotic, antimycotic or antiviral properties (Halama and Van Haluwin 2004; Shresta and Clair 2013; Odimegwu et al 2019), some of which may be of pharmaceutical interest (Müller 2001). Considering the great potential of secondary lichen metabolites produced by lichen mycobionts
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