Antimicrobial applications of lichens: secondary metabolites and green synthesis of silver nanoparticles: A review

Document Type : Narrative Review


1 Department of Biological Science, Faculty of Science, University of Kurdistan, Sanandaj, Kurdistan, Iran; Nanobiotechnology Department, Faculty of Innovative Science and Technology, Razi University, Kermanshah, Iran

2 Laser Research Centre, Faculty of Health Science, University of Johannesburg, Doornfontein, 2028, South Africa; Wellman Centre for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA; Department of Dermatology, Harvard Medical School, Boston, MA 02115, USA

3 Chembiotech Laboratories, Advanced Science and Technology Institute, Tenbury Wells, WR15 8FF, UK


Lichens produce a variety of unique extracellular secondary metabolites because these organisms are a life form comprising a complex symbiotic relationship between fungi and algae, which occur in many ecosystems. These compounds are present within the thallus and form crystals on the surface of the fungal hyphae. More than 800 different secondary metabolites, such as usnic acid, norstictic acid, atranorin, salazinic acid, stictic acid, atranorin, and chloroatranorin have been identified in lichens, most of which are found exclusively in lichen species. In recent years, lichens have received much attention for pharmaceutical and phytochemical applications. Lichens and their secondary metabolites have been investigated for various pharmacological activity, including antimicrobial, antioxidant, antiviral, anticancer, antigenotoxic, anti-inflammatory, antipyretic, and analgesic effects. This review discusses recent progress and challenges related to the antimicrobial activity of lichens, focusing on secondary metabolites of the leading medical species of lichen and the green synthesis of silver nanoparticles and nanocomposites.

Graphical Abstract

Antimicrobial applications of lichens: secondary metabolites and green synthesis of silver nanoparticles: A review


  • Lichens produce unique extracellular secondary metabolites such as usnic acid with antimicrobial activity.
  • One of the main antibacterial mechanisms for lichen extracts against Gram-positive bacteria is cell wall disruption.
  • The reduction of the metal ions and the stabilization of the resulting NPs can be carried out by both primary and secondary metabolites of lichens.
  • The suitable choice of lichen species can lead to the production of NPs with appropriate physicochemical properties.
  • The antimicrobial activity of metal or metal oxide NPs may be increased by the biosynthesis process.
  • Controlling the size and shape is critical to obtain effective antimicrobial activity of new formulations in physiological conditions.


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