Access to Anti-Biofilm Compounds from Endolichenic Fungi Using a Bioguided Networking Screening

Endolichenic Fungi: A Promising Medicinal Microbial Resource to Discover Bioactive Natural Molecules-An Update

Lichens are some of the most unique fungi and are naturally encountered as symbiotic biological organisms that usually consist of fungal partners (mycobionts) and photosynthetic organisms (green algae and cyanobacteria). Due to their distinctive growth environments, including hot deserts, rocky coasts, Arctic tundra, toxic slag piles, etc., they produce a variety of biologically meaningful and structurally novel secondary metabolites to resist external environmental stresses. The endofungi that live in and coevolve with lichens can also generate abundant secondary metabolites with novel structures, diverse skeletons, and intriguing bioactivities due to their mutualistic symbiosis with hosts, and they have been considered as strategically significant medicinal microresources for the discovery of pharmaceutical lead compounds in the medicinal industry. They are also of great importance in the fundamental research field of natural product chemistry. In this work, we conducted a comprehensive review and systematic evaluation of the secondary metabolites of endolichenic fungi regarding their origin, distribution, structural characteristics, and biological activity, as well as recent advances in their medicinal applications, by summarizing research achievements since 2015. Moreover, the current research status and future research trends regarding their chemical components are discussed and predicted. A systematic review covering the fundamental chemical research advances and pharmaceutical potential of the secondary metabolites from endolichenic fungi is urgently required to facilitate our better understanding, and this review could also serve as a critical reference to provide valuable insights for the future research and promotion of natural products from endolichenic fungi.

Lichen or Associated Micro-Organism Compounds Are Active against Human Coronaviruses

(1) Background: Since the emergence of SARS-CoV-2, responsible for the COVID-19 pandemic, efforts have been made to identify antiviral compounds against human coronaviruses. With the aim of increasing the diversity of molecule scaffolds, 42 natural compounds, of which 28 were isolated from lichens and 14 from their associated microorganisms (bacteria and fungi), were screened against human coronavirus HCoV-229E. (2) Methods: Antiviral assays were performed using HCoV-229E in Huh-7 and Huh-7/TMPRSS2 cells and SARS-CoV-2 in a Vero-81-derived clone with a GFP reporter probe. (3) Results: Four lichen compounds, including chloroatranol, emodin, perlatolic acid and vulpinic acid, displayed high activities against HCoV-229E (IC50 = 68.86, 59.25, 16.42 and 14.58 μM, respectively) and no toxicity at active concentrations. Kinetics studies were performed to determine their mode of action. The four compounds were active when added at the replication step. Due to their significant activity, they were further tested on SARS-CoV-2. Perlatolic acid was shown to be active against SARS-CoV-2. (4) Conclusions: Taken together, these results show that lichens are a source of interesting antiviral agents against human coronaviruses. Moreover, perlatolic acid might be further studied for its pan-coronavirus antiviral activity.

Antibiofilm Activity of Invasive Plants against Candida albicans: Focus on Baccharis halimifolia Essential Oil and Its Compounds

The extracts of five invasive plants were investigated for antifungal and antibiofilm activities against Candida albicans, C. glabrata, C. krusei, and C. parapsilosis. The antifungal activity was evaluated using the microdilution assay and the antibiofilm effect by measurement of the metabolic activity. Ethanol and ethanol-water extracts of Reynoutria japonica leaves inhibited 50 % of planktonic cells at 250 μg mL-1 and 15.6 μg mL-1 , respectively. Ethanol and ethanol-water extracts of Baccharis halimifolia inhibited >75 % of the mature biofilm of C. albicans at 500 μg mL-1 . The essential oil (EO) of B. halimifolia leaves was the most active (50 % inhibition (IC50 ) at 4 and 74 μg mL-1 against the maturation phase and 24 h old-biofilms of C. albicans, respectively). Oxygenated sesquiterpenes were the primary contents in this EO (62.02 %), with β-caryophyllene oxide as the major component (37 %). Aromadendrene oxide-(2), β-caryophyllene oxide, and (±)-β-pinene displayed significant activities against the maturation phase (IC50 =9-310 μ mol l-1 ) and preformed 24 h-biofilm (IC50 =38-630 μ mol l-1 ) of C. albicans with very low cytotoxicity for the first two compounds. C. albicans remained the most susceptible species to this EO and its components. This study highlighted for the first time the antibiofilm potential of B. halimifolia, its EO and some of its components.