Lichens and biofilms: Common collective growth imparts similar developmental strategies

Lichens are traditionally defined as a symbiotic relationship between fungi and algae and/or cyanobacteria. This union forms a unique structure called the thallus, which attaches to surfaces such as rocks and tree bark. Recent reports challenge the view that lichens are comprised of one fungus and one photobiont, and instead suggest that they are a consortium of microbes. Much of lichen biology remains unknown as most of our knowledge of lichens is limited to morphological characteristics with little to no functional analysis of lichen genes. However, lichens and biofilms share many similar physiological traits which when compared may assist in our understanding of lichens. Similarities between the two are rooted in their lifestyle, where these microbes and their extracellular products attach themselves to a surface and grow in a community structure. Biofilms and lichens alike have distinct features that allow for their lifestyle and identification, such as specific developmental patterns, formation of an extracellular matrix, and their ability to resist abiotic stressors. We argue here that one can gain insight into the cellular processes and evolutionary origins of lichens, which are currently undetermined, by applying knowledge gleaned from studies on microbial biofilms, with a particular focus on fungal biofilms.