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Ten samples of tropical lichens collected from Doi Inthanon, Thailand, were explored for the diversity of their bacterial microbiomes through 16S rRNA-based metagenomics analysis. The five predominant lichen-associated bacteria belonged to the phyla Proteobacteria (31.84%), Planctomycetota (17.08%), Actinobacteriota (15.37%), Verrucomicrobiota (12.17%), and Acidobacteriota (7.87%). The diversity analysis metric showed that Heterodermia contained the highest bacterial species richness. Within the lichens, Ramalina conduplicans and Cladonia rappii showed a distinct bacterial community from the other lichen species. The community of lichen-associated actinobacteria was investigated as a potential source of synthesized biologically active compounds. From the total Operational Taxonomic Units (OTUs) found across the ten different lichen samples, 13.21% were identified as actinobacteria, including the rare actinobacterial genera that are not commonly found, such as Pseudonocardia, Kineosporia, Dactylosporangium, Amycolatopsis, Actinoplanes, and Streptosporangium. Evaluation of the pretreatment method (heat, air-drying, phenol, and flooding) and isolation media used for the culture-dependent actinobacterial isolation revealed that the different pretreatments combined with different isolation media were effective in obtaining several species of actinobacteria. However, metagenomics analyses revealed that there were still several strains, including rare actinobacterial species, that were not isolated. This research strongly suggests that lichens appear to be a promising source for obtaining actinobacteria., (© 2023. The Author(s).)

A total of 37 actinobacteria were isolated from eighteen lichen samples collected in Thailand. Based on the 16S rRNA gene sequences, they were identified into five genera including Actinoplanes (1 strain), Actinomadura (1 strain), Pseudosporangium (1 strain), Wangella (1 strain) and Streptomyces (33 strains). Among these isolates, strain Ptm05 T , Ptm01 and Ptm12 showed low 16S rRNA gene similarity and was selected for the further taxonomic study using the polyphasic approach. These strains showed the highest 16S rRNA gene sequence similarity with Streptomyces sparsogenes ATCC 25498 T (97.44-97.72%). Strain Ptm05 T was selected for the type strain. The chemical cell composition of the strain was similar to the members of Streptomyces genus. LL-diaminopimelic acids were detected in the peptidoglycan. Menaquinones were MK-9(H 8 ) and MK-9(H 6 ). Phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, one unidentified phospholipid, one unidentified glycolipid and one unidentified lipid were detected as the polar lipids. The predominant cellular fatty acids are anteiso-C 15:0 , iso-C 15:0 , iso-C 16:0 , iso-C 17:0 and C 16:0 . The dDNA-DNA hybridization values among strain Ptm05 T and its closely related Streptomyces type strains were 17.2-18.0%. In addition, the ANIb and ANIm between strain Ptm05 T and related Streptomyces type strains were ranged from 75.69 to 76.13% and 85.21 to 85.35%, respectively. Based on phenotypic and genomic evidence, strain Ptm05 T (= TBRC 14546 T  = NBRC 115203 T ) represents the novel species of the genus Streptomyces for which the name Streptomyces parmotrematis sp. nov. is proposed. This study showed that the lichens are the promising source of the novel actinobacterial taxa., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The actinobacteria strain Lp03 was isolated from the lichen, Pyxine cocoes, collected from Lumpini Park, Bangkok, Thailand. Based on the polyphasic approach, strain Lp03 was identified as Streptomyces parvulus. Actinomycin D produced by this strain exhibited antibacterial activity against Bacillus cereus (MIC 1.56 µg/ml), Bacillus subtilis (MIC 5 µg/ml), Escherichia coli (MIC 12.5 µg/ml), Kocuria rhizophila (MIC 0.076 ng/ml), Klebsiella pneumoniae (MIC 0.78 µg/ml), Staphylococcus aureus (MIC 9.76 ng/ml), Staphylococcus epidermidis (MIC 9.76 ng/ml), and Mycobacterium tuberculosis (MIC 12.5 µg/ml). Actinomycin D was inactive against Acinetobacter baumannii, but the new finding revealed that it showed activity against A. baumannii when combined with ß-naphthylamide (PNßN), the efflux inhibitor. Antiparasitic activity was observed against Plasmodium falciparum with an IC50 value of 14.8 ng/ml. It showed cytotoxicity against Vero cells, NCI-H187, KB, and MCF-7 with IC50 values of 125, 0.694, 18.4 ng/ml, and 21.94 µg/ml, respectively. The genome of S. parvulus harbors a high diversity of biosynthetic gene clusters for secondary metabolites (BGCs). The actinomycin BGCs could be detected in all publicly available genomes of S. parvulus but could be varied among the strains. This study is the first record for the complete taxonomic study and bioactive compound produced by S. parvulus isolated from the lichen. [ABSTRACT FROM AUTHOR]