Bacteria and Lichens

In this project we will study bacteria that are associated with lichens. Despite the diversity of lichenized these long- living and stress-tolerant mutualistic symbioses of fungi with algae/cyanobacteria, their interactions with bacteria are still under-explored. In the planned project, we focus on selected representatives of lichens on diverse substrates and from different phylogenetic groups. First, we will analyse the structural and functional diversity of bacteria, using a combination of DNA-based, culture-based and microscopical approaches. We will then test experimentally whether bacterial strains can act synergistically or detrimentally on the lichen symbioses or have effects on the survival of presymbiotic stages, respectively. As endosymbionts were found in other fungal groups, we will also investigate whether these may also occur in lichens. We hypothesize that certain bacteria are ecologically relevant to lichens and expect to find new bacterial species, some of which may be closely related to opportunistic human-pathogenic organisms. The investigation of lichen associated bacteria may also be interesting in the search of new bioactive properties. This question which will be addressed with experimental assays.

In this project we studied bacteria that are associated with lichens. Despite the diversity of these long-living and stress-tolerant mutualistic symbioses of fungi with algae/cyanobacteria, their interactions with bacteria were still under-explored. To analyse the structural diversity of lichen-associated bacterial communities we used molecular fingerprints and fluorescence in situ hybridization (FISH) combined with confocal laser scanning microscopy (CLSM). All selected representatives from different phylogenetic lichen groups (Cladonia, Lecanora, Lobaria, Umbilicaria) were highly colonized up to 108 cells g-1 fw with diverse bacterial communities. We found Alphaproteobacteria as a dominant component in each of the investigated lichen, and a certain degree of specificity was also observed. Further, we found that lichens harbour novel bacterial lineages, and we described Frondihabitans cladoniiphilia as new species to science. Bacterial communities form specific biofilm-like structures in/on lichen tissues. Their function is still pending further research. Investigations of bacterial isolates and functional genes suggested that they are involved in nitrogen fixation, antibiosis and nutrient cycling. Environmental proteomics was used to gain a first insight into bacterial activity. Our structural data were confirmed by this approach: more spectra were assigned to prokaryotic proteins (10%) than to the green algal photobiont (3.5%). A major proportion of bacterial proteins appeared to be involved in posttranslational modifications and protein turnover. Furthermore, several proteins found seem to be involved in synthesis of secondary metabolites. The high abundance, diversity, potential functions of bacteria underlie the hypothesis of their involvement in lichen symbioses. We suggest that the traditional lichen symbiosis as a partnership of fungi with photoautotrophic partners needs to be expanded to include the bacterial associates. In an additional approach, the potential of lichen- associated bacteria for biotechnology was assessed. Lichens harbour biopolymer-producing bacteria, diverse exoenzyme-producing bacteria a well as an extremely high proportion of bacterial antagonists against plant pathogens.