Chronicle of Research into Lichen-Associated Bacteria

Phytochemical composition, biological activity and anti-inflammatory potential of acetone extract from the lichen Platismatia glauca (L.) W.L. Culb. & C.F. Culb

This investigation examined the antioxidant, antimicrobial, cytotoxic, and anti-inflammatory activities of the acetone extract of the lichen Platismatia glauca (L.) W.L. Culb. & C.F. Culb. (PGAE). The phytochemical study of PGAE showed presence of seven compounds: salazinic acid, β-orcinol carboxylic acid, 3-hydroxyphysodalic acid, physodalic acid, physodic acid, atranorin, and chloroatranorin. The antimicrobial potential was determined by microdilution which showed that S. aureus was most sensitive to the effect of PGAE with MIC value 0.312 mg/ml. Antioxidant activity was evaluated by using DPPH method. The obtained IC50 value for PGAE was 194.30 ± 3.32 µg/ml. The cytotoxic effect of the extract was evaluated by MTT test and the strongest activity was towards human epithelial carcinoma cells with IC50 value of 59.10 ± 0.46 µg/ml. The findings revealed that the application of lichen extracts decreased the paw edoema in a dose-dependent manner at 1, 2, 3, and 4 h following carrageenan administration.

Microbial occurrence and symbiont detection in a global sample of lichen metagenomes

In lichen research, metagenomes are increasingly being used for evaluating symbiont composition and metabolic potential, but the overall content and limitations of these metagenomes have not been assessed. We reassembled over 400 publicly available metagenomes, generated metagenome-assembled genomes (MAGs), constructed phylogenomic trees, and mapped MAG occurrence and frequency across the data set. Ninety-seven percent of the 1,000 recovered MAGs were bacterial or the fungal symbiont that provides most cellular mass. Our mapping of recovered MAGs provides the most detailed survey to date of bacteria in lichens and shows that 4 family-level lineages from 2 phyla accounted for as many bacterial occurrences in lichens as all other 71 families from 16 phyla combined. Annotation of highly complete bacterial, fungal, and algal MAGs reveals functional profiles that suggest interdigitated vitamin prototrophies and auxotrophies, with most lichen fungi auxotrophic for biotin, most bacteria auxotrophic for thiamine and the few annotated algae with partial or complete pathways for both, suggesting a novel dimension of microbial cross-feeding in lichen symbioses. Contrary to longstanding hypotheses, we found no annotations consistent with nitrogen fixation in bacteria other than known cyanobacterial symbionts. Core lichen symbionts such as algae were recovered as MAGs in only a fraction of the lichen symbioses in which they are known to occur. However, the presence of these and other microbes could be detected at high frequency using small subunit rRNA analysis, including in many lichens in which they are not otherwise recognized to occur. The rate of MAG recovery correlates with sequencing depth, but is almost certainly influenced by biological attributes of organisms that affect the likelihood of DNA extraction, sequencing and successful assembly, including cellular abundance, ploidy and strain co-occurrence. Our results suggest that, though metagenomes are a powerful tool for surveying microbial occurrence, they are of limited use in assessing absence, and their interpretation should be guided by an awareness of the interacting effects of microbial community complexity and sequencing depth.

Bacteriomic Profiles of Rock-Dwelling Lichens from the Venezuelan Guiana Shield and the South African Highveld Plateau

Lichens are not only fungal-algal symbiotic associations but also matrices for association with bacteria, and the bacterial diversity linked to lichens has been receiving more attention in studies. This study compares the diversity and possible metabolism of lichen-associated bacteria from saxicolous foliose and fruticose taxa Alectoria, Canoparmelia, Crocodia, Menegazzia, Usnea, and Xanthoparmelia from the Venezuelan Guiana Shield and the South African Highveld Plateau. We used DNA extractions from the lichen thalli to amplify the eukaryotic 18S rRNA gene (rDNA) and the V3-V4 region of the bacterial 16S rDNA, of which amplicons were then Sanger- and MiSeq-sequenced, respectively. The V3-V4 sequences of the associated bacteria were grouped into operational taxonomic units (OTUs) ascribed to twelve bacterial phyla previously found in the rock tripe Umbilicaria lichens. The bacterial OTUs emphasized the uniqueness of each region, while, at the species and higher ranks, the regional microbiomes were shown to be somewhat similar. Nevertheless, regional biomarker OTUs were screened to predict relevant metabolic pathways, which implicated different regional metabolic features.

Actinoplanes pyxinae sp. nov., a new lichen-derived rare actinobacterium exhibiting antimicrobial and anticancer activity

A novel lichen-derived actinobacterium, designated Pm04-4T, was isolated from Pyxine cocoes (Sw.) Nyl. lichen collected from Chaiyaphum, Thailand. A polyphasic approach was used to describe the taxonomic position of the strain. The strain had morphological and chemotaxonomic properties similar to members of the genus Actinoplanes. It produced sporangia on the substrate mycelia. Meso-diaminopimelic acid, galactose, glucose and mannose were detected in the whole-cell hydrolysate of the strain. The major menaquinone was MK-9(H4). The polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol and phosphatidylinositol mannoside. The predominant cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. Strain Pm04-4T showed the highest 16S rRNA gene sequence similarity to Actinoplanes akusuensis TRM 8003T (99.0 %). In the phylogenomic tree, strain Pm04-4T was positioned close to A. aksuensis TRM88003T, A. maris M416T, A. polyasparticus TRM66264T, A. hotanensis TRM88002T, A. abujensis DSM 45518T, A. bogorensis NBRC 110975T, A. brasiliensis DSM 43805T, A. lichenicola LDG1-01T and A. ovalisporus LDG1-06T. The average nucleotide identity and digital DNA-DNA hybridization values between strain Pm04-4T and its closely related neighbours were below the threshold values for describing new species. Moreover, the strain could be distinguished from its closely related type strains by phenotypic properties. Based on genotypic and phenotypic evidence, it can be concluded that strain Pm04-4T is a representative of a new Actinoplanes species for which the name Actinoplanes pyxinae sp. nov. is proposed. The type strain is Pm04-4T (=TBRC 16207T=NBRC 115836T). The type strain exhibited activity against Staphylococcus aureus ATCC 25923 as well as four yeast strains, namely Candida albicans TISTR 5554, Candida glabrata TISTR 5006, Candida krusei TISTR 5351 and Candida parapsilosis TISTR 5007. It also showed cytotoxicity against Caco-2, MNT-1 and MCF-7 cancer cells.