Analysis of the Peltigera membranacea metagenome indicates that lichen-associated bacteria are involved in phosphate solubilization

Cyanobacteria in Terrestrial Symbiotic Systems

“…Also the genome of the cyanobiont of the water fern Azolla ("Nostoc azollae" 0708) has been sequenced (Vigil-Stenman et al 2015), and genomic sequences of several lichen-associated Nostoc genotypes are expected to become available soon (Grube et al 2014). Metagenome sequencing of cyanolichens is also providing new insights into the genetic diversity of cyanobacterial symbioses (Kampa et al 2013;Sigurbjörnsdóttir et al 2015).…”

Are lichens potential natural reservoirs for plant pathogens?

“…In many species, either or both partners produce secondary metabolites with antibacterial activity, thus providing a somewhat selective environment in which complex bacterial communities thrive, some in biofilm‐like surface communities (Grube et al ., ) and others endothallically, below the surface of extracellular polysaccharides (Cardinale et al ., ; Grube et al ., ). Thus, lichens are hosts to large populations of bacteria whose identity and role in the lichen symbiotic association have been gradually emerging in recent years (Hodkinson and Lutzoni, ; Sigurbjörnsdóttir et al ., ). Although there is considerable inter‐species and inter‐study variability, it has become clear that most lichens harbour a sizeable, complex, Proteobacteria‐dominated microbiota, with dominant families typically comprising the Rhizobiaceae, Methylobacteraceae, Sphingomonadaceae, Acetobacteraceae, Rhodospirillaceae, Comamonadaceae and Burkholderiaceae (Aschenbrenner et al ., ; Sigurbjörnsdóttir et al ., ).…”

“…Thus, lichens are hosts to large populations of bacteria whose identity and role in the lichen symbiotic association have been gradually emerging in recent years (Hodkinson and Lutzoni, ; Sigurbjörnsdóttir et al ., ). Although there is considerable inter‐species and inter‐study variability, it has become clear that most lichens harbour a sizeable, complex, Proteobacteria‐dominated microbiota, with dominant families typically comprising the Rhizobiaceae, Methylobacteraceae, Sphingomonadaceae, Acetobacteraceae, Rhodospirillaceae, Comamonadaceae and Burkholderiaceae (Aschenbrenner et al ., ; Sigurbjörnsdóttir et al ., ). Typically, taxa more commonly associated with phytopathogens, such as members of the Xanthomonadaceae, Pseudomonadaceae and Enterobacteriaceae, are also present, albeit in lower numbers.…”

“…Among the bacteria indicated by metagenomic or amplicon‐based analysis to be present in lichen‐associated microbiomes that have not been cultured to our knowledge are a few plant pathogens. For example, both functional genes and 16S rDNA from Xanthomonas and its close relative Xylella were observed in the membranous dog lichen ( Peltigera membranacea ) metagenome (Sigurbjörnsdóttir et al ., ), but have not, as yet, been cultured from that species. The finding of Xanthomonas ‐like organisms in lichens is interesting because Xanthomonas spp.…”

“…Our recent analysis of a partial shotgun metagenome of the microbiome associated with Pe. membranacea (Sigurbjörnsdóttir et al ., ) yielded a number of multiple hits on several genes involved in lichen secondary metabolite resistance, inorganic phosphate mobilization, biopolymer degradation and several other potentially important functions in thallus colonization and symbiosis, as well as several genes likely to play a role in plant pathogenicity. Among the plant virulence genes found in the metagenome are several homologues of type III and type IV secretion systems from diverse bacteria, including xanthomonads, burkholderiae, sphingomonads and acidobacters.…”