Lichen-associated bacteria transform antibacterial usnic acid to products of lower antibiotic activity

Endophytic microorganisms in lichen: rising stars in the biomedicine field deserving broader recognition

Lichens are renowned for their ability to thrive in extreme environments and for producing unique metabolites with considerable bioactive potential. However, their medicinal value remains largely underexplored, primarily due to slow growth rates and habitat specificity. Notably, endolichenic microorganisms, particularly fungi, are the predominant producers of these bioactive compounds, which exhibit antimicrobial, antiviral, and anticancer properties. Investigating these microorganisms and their metabolites presents promising biomedical opportunities, underscoring the importance of sustainably utilizing lichen resources and discovering novel compounds. This paper reviews the diversity and bioactive potential of endophytic microorganisms in lichens, providing valuable insights for the exploration of natural resources.

In vitro, in vivo and in silico anticancer activity and toxicity of Usnic acid extracted from the mycobiont culture of Usnea baileyi

Lichen has widespread uses in indigenous medicinal traditions, and it has been used to treat various conditions. Among the various active compounds in the lichen, Usnic acid has unique biological activities. However, the toxicology and the mechanism of action of Usnic acid need to be examined in detail to the extent of clinical trials. Hence, the present research is aimed to isolate usnic acid from the mycobiont culture of Usnea baileyi lichen and explore its toxicological properties and those of pharmacological importance. The methanolic extract of these mycobiont cultures has shown the presence of Usnic acid via column chromatography. The Usnic acid was computationally evaluated using molecular docking studies (GLIDE docking) and MMGBSA energy calculations. The results obtained from TLC, LC-MS, UV-VIS spectrophotometer, NMR spectroscopy (1H and 13c), and FT-IR indicated the presence of Usnic acid. An acute toxicity analysis by an in vivo study using a zebrafish animal model showed acute toxicity. The standard disc diffusion and DPPH assay suggested an antimicrobial and antioxidant activity with this lichen compound. The in vitro analysis of Usnic acid in G361 skin cancer cell lines demonstrated its anticancer potential against malignant melanoma. Furthermore, a molecular in silico study returned a good docking score of -7.977, and the MMGBSA free energy was measured as -18 and -30. Therefore, further extensive research on Usnic acid might lead to the development of novel anticancer drugs from the natural sources.

Nanostructured Poly-l-lactide and Polyglycerol Adipate Carriers for the Encapsulation of Usnic Acid: A Promising Approach for Hepatoprotection

The present study investigates the utilization of nanoparticles based on poly-l-lactide (PLLA) and polyglycerol adipate (PGA), alone and blended, for the encapsulation of usnic acid (UA), a potent natural compound with various therapeutic properties including antimicrobial and anticancer activities. The development of these carriers offers an innovative approach to overcome the challenges associated with usnic acid's limited aqueous solubility, bioavailability, and hepatotoxicity. The nanosystems were characterized according to their physicochemical properties (among others, size, zeta potential, thermal properties), apparent aqueous solubility, and in vitro cytotoxicity. Interestingly, the nanocarrier obtained with the PLLA-PGA 50/50 weight ratio blend showed both the lowest size and the highest UA apparent solubility as well as the ability to decrease UA cytotoxicity towards human hepatocytes (HepG2 cells). This research opens new avenues for the effective utilization of these highly degradable and biocompatible PLLA-PGA blends as nanocarriers for reducing the cytotoxicity of usnic acid.

The Tripartite Lichen Ricasolia virens: Involvement of Cyanobacteria and Bacteria in Its Morphogenesis

Ricasolia virens is an epiphytic lichen-forming fungus mainly distributed in Western Europe and Macaronesia in well-structured forests with ecological continuity that lack eutrophication. It is considered to be threatened or extinct in many territories in Europe (IUCN). Despite its biological and ecological relevance, studies on this taxon are scarce. The thalli are tripartite, and the mycobiont has a simultaneous symbiotic relationship with cyanobacteria and green microalgae, which represent interesting models to analyse the strategies and adaptations resulting from the interactions of lichen symbionts. The present study was designed to contribute to a better understanding of this taxon, which has shown a clear decline over the last century. The symbionts were identified by molecular analysis. The phycobiont is Symbiochloris reticulata, and the cyanobionts (Nostoc) are embedded in internal cephalodia. Light, transmission electron and low-temperature scanning microscopy techniques were used to investigate the thallus anatomy, ultrastructure of microalgae and ontogeny of pycnidia and cephalodia. The thalli are very similar to its closest relative, Ricasolia quercizans. The cellular ultrastructure of S. reticulata by TEM is provided. Non-photosynthetic bacteria located outside the upper cortex are introduced through migratory channels into the subcortical zone by the splitting of fungal hyphae. Cephalodia were very abundant, but never as external photosymbiodemes.

A roadmap for the creation of synthetic lichen

Lichens represent a charismatic corner of biology that has a rich history of scientific exploration, but to which modern biological techniques have been sparsely applied. This has limited our understanding of phenomena unique to lichen, such as the emergent development of physically coupled microbial consortia or distributed metabolisms. The experimental intractability of natural lichens has prevented studies of the mechanistic underpinnings of their biology. Creating synthetic lichen from experimentally tractable, free-living microbes has the potential to overcome these challenges. They could also serve as powerful new chassis for sustainable biotechnology. In this review we will first briefly introduce what lichen are, what remains mysterious about their biology, and why. We will then articulate the scientific insights that creating a synthetic lichen will generate and lay out a roadmap for how this could be achieved using synthetic biology. Finally, we will explore the translational applications of synthetic lichen and detail what is needed to advance the pursuit of their creation.

Synthesis and Characterization of Ferrous and Copper Nanoparticles from E-Waste Using Biological Reduction by Lichen-Associated Bacteria and Their Application in Antifouling Activity

The largest and fastest growing industry in the world is electronic industries and the generation of waste are emerging problem. Electronic wastes are the source of precious metals that contributes 40 to 50 times more than the ore extracted from mines. The recycling of the waste is very important as it can protect the earth's natural resources. There are various methods for recycling e-waste such as chemical, fire, physical, and mechanical method. Currently, chemical treatment is in practice for recycling but, due to the usage of inorganic chemicals, it gives more environmental issues. Therefore, this paper used the biological method to prepare the nanoparticle from e-waste as it is an eco-friendly method. The copper and ferrous nanoparticle was extracted from the e-waste and biologically reduced using lichen-associated bacterial such as Parmotrema tintorum and P. recticulatum. The characteristics of these nanoparticles such as size, shape, and functional group were analyzed using UV, PSA, SEM, and FTIR respectively. The size of the synthesized particle was in the range of 10-100 nm using PSA. At the 2.5% concentration, the synthesis of ferrous nanoparticles was confirmed by the peak value obtained at 430 nm and 540 nm for copper nanoparticles. The antifouling properties of synthesized nanoparticles were analyzed by colliding them with the paint and applying to the iron surface. In recent research, the nanomaterials were able to use to reduce the fouling activity, also prevent harmful effects to the other marine species and the resistance of some microorganisms to antifoulants. This study helps to prevent environmental contaminants by using the copper and ferrous nanoparticle substances synthesized from the e-waste materials with the help of bacterial reduction.

Chronicle of Research into Lichen-Associated Bacteria

Lichens are mutually symbiotic systems consisting of fungal and algal symbionts. While diverse lichen-forming fungal species are known, limited species of algae form lichens. Plasticity in the combination of fungal and algal species with different eco-physiological properties may contribute to the worldwide distribution of lichens, even in extreme habitats. Lichens have been studied systematically for more than 200 years; however, plasticity in fungal-algal/cyanobacterial symbiotic combinations is still unclear. In addition, the association between non-cyanobacterial bacteria and lichens has attracted attention in recent years. The types, diversity, and functions of lichen-associated bacteria have been studied using both culture-based and culture-independent methods. This review summarizes the history of systematic research on lichens and lichen-associated bacteria and provides insights into the current status of research in this field.

Rhizocarpon geographicum Lichen Discloses a Highly Diversified Microbiota Carrying Antibiotic Resistance and Persistent Organic Pollutant Tolerance

As rock inhabitants, lichens are exposed to extreme and fluctuating abiotic conditions associated with poor sources of nutriments. These extreme conditions confer to lichens the unique ability to develop protective mechanisms. Consequently, lichen-associated microbes disclose highly versatile lifestyles and ecological plasticity, enabling them to withstand extreme environments. Because of their ability to grow in poor and extreme habitats, bacteria associated with lichens can tolerate a wide range of pollutants, and they are known to produce antimicrobial compounds. In addition, lichen-associated bacteria have been described to harbor ecological functions crucial for the evolution of the lichen holobiont. Nevertheless, the ecological features of lichen-associated microbes are still underestimated. To explore the untapped ecological diversity of lichen-associated bacteria, we adopted a novel culturomic approach on the crustose lichen Rhizocarpon geographicum. We sampled R. geographicum in French habitats exposed to oil spills, and we combined nine culturing methods with 16S rRNA sequencing to capture the greatest bacterial diversity. A deep functional analysis of the lichen-associated bacterial collection showed the presence of a set of bacterial strains resistant to a wide range of antibiotics and displaying tolerance to Persistent Organic Pollutants (POPs). Our study is a starting point to explore the ecological features of the lichen microbiota.

An insight into an intriguing oxidative biotransformation pathway of 5-O-caffeoylquinic acid by a gut bacterium

Microbiota is known to play a pivotal role in generating bioavailable and bioactive low-molecular-weight metabolites from dietary polyphenols. 5-O-caffeoylquinic acid (5-CQA), one of the main polyphenols found in human diet, was submitted to a resting cell biotransformation study using three gut bacteria species Lactobacillus reuteri, Bacteroides fragilis and Bifidobacterium longum. These bacteria were selected according to their belonging to the main phyla found in human gut microbiota. Our study highlighted the ability of only one of the strains studied, L. reuteri, to bioconverse 5-CQA into various metabolites due to the expression of the cinnamoyl esterase enzyme as the first step. Interestingly, one known natural compound, esculetin, was described for the first time as a 5-CQA-derived metabolite after conversion by a gut bacterium, the other metabolites had already been reported. This evidence highlighted an interesting oxidative pathway occurring in vivo by intestinal microbiota leading to esculetin. This molecule was also identified after electrochemical and enzymatic oxidations of caffeic acid. The oxidation capacity of L. reuteri led to less diverse metabolites in comparison to those obtained either electrochemically and enzymatically where dimers and trimers were reported. Thus, esculetin may have interesting and benefical biological effects on gut microbiota, which should be further evaluated. Novel synbiotics could be formulated from the association of L. reuteri with 5-CQA.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.

Establishment of Agrobacterium tumefaciens-Mediated Transformation of Cladonia macilenta, a Model Lichen-Forming Fungus

Despite the fascinating biology of lichens, such as the symbiotic association of lichen-forming fungi (mycobiont) with their photosynthetic partners and their ability to grow in harsh habitats, lack of genetic tools manipulating mycobiont has hindered studies on genetic mechanisms underpinning lichen biology. Thus, we established an Agrobacterium tumefaciens-mediated transformation (ATMT) system for genetic transformation of a mycobiont isolated from Cladonia macilenta. A set of combinations of ATMT conditions, such as input biomass of mycobiont, co-cultivation period with Agrobacterium cells, and incubation temperature, were tested to identify an optimized ATMT condition for the C. macilenta mycobiont. As a result, more than 10 days of co-cultivation period and at least 2 mg of input biomass of the mycobiont were recommended for an efficient ATMT, owing to extremely slow growth rate of mycobionts in general. Moreover, we examined T-DNA copy number variation in a total of 180 transformants and found that 88% of the transformants had a single copy T-DNA insertion. To identify precise T-DNA insertion sites that interrupt gene function in C. macilenta, we performed TAIL-PCR analyses for selected transformants. A hypothetical gene encoding ankyrin repeats at its C-terminus was interrupted by T-DNA insertion in a transformant producing dark-brown colored pigment. Although the identification of the pigment awaits further investigation, this proof-of-concept study demonstrated the feasibility of use of ATMT in construction of a random T-DNA insertion mutant library in mycobionts for studying genetic mechanisms behind the lichen symbiosis, stress tolerance, and secondary metabolite biosynthesis.