Phylogenetic Diversity, Antimicrobial and Antioxidant Potential and Identification of Bioactive Compounds from Culturable Endophytic Fungi Associated with Mangrove Bruguiera sexangula (Lour.) Poir

Exploring the antioxidant potential of endophytic fungi: a review on methods for extraction and quantification of total antioxidant capacity (TAC)

Endophytic fungi have emerged as a significant source of natural products with remarkable bioactivities. Recent research has identified numerous antioxidant molecules among the secondary metabolites of endophytic fungi. These organisms, whether unicellular or micro-multicellular, offer the potential for genetic manipulation to enhance the production of these valuable antioxidant compounds, which hold promise for promoting health, vitality, and various biotechnological applications. In this study, we provide a critical review of methods for extracting, purifying, characterizing, and estimating the total antioxidant capacity (TAC) of endophytic fungi metabolites. While many endophytes produce metabolites similar to those found in plants with established symbiotic associations, we also highlight the existence of novel metabolites with potential scientific interest. Additionally, we discuss how advancements in nanotechnology have opened new avenues for exploring nanoformulations of endophytic metabolites in future studies, offering opportunities for diverse biological and industrial applications.

Exploring the diversity, bioactivity of endophytes, and metabolome in Synsepalum dulcificum

Synsepalum dulcificum exhibits high edible and medicinal value; however, there have been no reports on the exploration of its endophyte resources. Here, we conducted analyses encompassing plant metabolomics, microbial diversity, and the biological activities of endophytic metabolites in S. dulcificum. High-throughput sequencing identified 4,913 endophytic fungal amplicon sequence variants (ASVs) and 1,703 endophytic bacterial ASVs from the roots, stems, leaves, flowers, and fruits of S. dulcificum. Fungi were classified into 5 phyla, 24 classes, 75 orders, 170 families, and 313 genera, while bacteria belonged to 21 phyla, 47 classes, 93 orders, 145 families, and 232 genera. Furthermore, there were significant differences in the composition and content of metabolites in different tissues of S. dulcificum. Spearman's correlation analysis of the differential metabolites and endophytes revealed that the community composition of the endophytes correlated with plant-rich metabolites. The internal transcribed spacer sequences of 105 isolates were determined, and phylogenetic analyses revealed that these fungi were distributed into three phyla (Ascomycota, Basidiomycota, and Mucoromycota) and 20 genera. Moreover, 16S rDNA sequencing of 46 bacteria revealed they were distributed in 16 genera in three phyla: Actinobacteria, Proteobacteria, and Firmicutes. The antimicrobial activities (filter paper method) and antioxidant activity (DPPH and ABTS assays) of crude extracts obtained from 68 fungal and 20 bacterial strains cultured in different media were evaluated. Additionally, the α-glucosidase inhibitory activity of the fungal extracts was examined. The results showed that 88.6% of the strains exhibited antimicrobial activity, 55.7% exhibited antioxidant activity, and 85% of the fungi exhibited α-glucosidase inhibitory activity. The research suggested that the endophytes of S. dulcificum are highly diverse and have the potential to produce bioactive metabolites, providing abundant species resources for developing antibiotics, antioxidants and hypoglycemic drugs.

"Mini-community" simulation revealed the differences of endophytic fungal communities between the above- and below-ground tissues of Ephedra sinica Stapf

The microecology of endophytic fungi in special habitats, such as the interior of different tissues from a medicinal plant, and its effects on the formation of metabolites with different biological activities are of great importance. However, the factors affecting fungal community formation are unclear. This study is the first to utilize "mini-community" remodeling to understand the above phenomena. First, high-throughput sequencing technology was applied to explore the community composition and diversity of endophytic fungi in the above-ground tissues (Ea) and below-ground tissues (Eb) of Ephedra sinica. Second, fungi were obtained through culture-dependent technology and used for "mini-community" remodeling in vitro. Then, the effects of environmental factors, partner fungi, and plant tissue fluid (internal environment) on endophytic fungal community formation were discussed. Results showed that environmental factors played a decisive role in the selection of endophytic fungi, that is, in Ea and Eb, 93.8% and 25.3% of endophytic fungi were halophilic, respectively, and 10.6% and 60.2% fungi were sensitive to high temperature (33 °C), respectively. Meanwhile, pH had little effect on fungal communities. The internal environment of the plant host further promoted the formation of endophytic fungal communities.

Insights into the phylogenetic diversity, biological activities, and biosynthetic potential of mangrove rhizosphere Actinobacteria from Hainan Island

Mangrove rhizosphere soils host diverse Actinobacteria tolerant to numerous stresses and are inevitably capable of exhibiting excellent biological activity by producing impressive numbers of bioactive natural products, including those with potential medicinal applications. In this study, we applied an integrated strategy of combining phylogenetic diversity, biological activities, and biosynthetic gene clusters (BGCs) screening approach to investigate the biotechnological importance of Actinobacteria isolated from mangrove rhizosphere soils from Hainan Island. The actinobacterial isolates were identifified using a combination of colony morphological characteristics and 16S rRNA gene sequence analysis. Based on the results of PCR-detected BGCs screening, type I and II polyketide synthase (PKS) and non-ribosomal synthetase (NRPS) genes were detected. Crude extracts of 87 representative isolates were subjected to antimicrobial evaluation by determining the minimum inhibitory concentration of each strain against six indicator microorganisms, anticancer activities were determined on human cancer cell lines HepG2, HeLa, and HCT-116 using an MTT colorimetric assay, and immunosuppressive activities against the proliferation of Con A-induced T murine splenic lymphocytes in vitro. A total of 287 actinobacterial isolates affiliated to 10 genera in eight families of six orders were isolated from five different mangrove rhizosphere soil samples, specififically, Streptomyces (68.29%) and Micromonospora (16.03%), of which 87 representative strains were selected for phylogenetic analysis. The crude extracts of 39 isolates (44.83%) showed antimicrobial activity against at least one of the six tested indicator pathogens, especially ethyl acetate extracts of A-30 (Streptomyces parvulus), which could inhibit the growth of six microbes with MIC values reaching 7.8 μg/mL against Staphylococcus aureus and its resistant strain, compared to the clinical antibiotic ciproflfloxacin. Furthermore, 79 crude extracts (90.80%) and 48 (55.17%) of the isolates displayed anticancer and immunosuppressive activities, respectively. Besides, four rare strains exhibited potent immunosuppressive activity against the proliferation of Con A-induced T murine splenic lymphocyte in vitro with an inhibition rate over 60% at 10 μg/mL. Type I and II polyketide synthase (PKS) and non-ribosomal synthetase (NRPS) genes were detected in 49.43, 66.67, and 88.51% of the 87 Actinobacteria, respectively. Signifificantly, these strains (26 isolates, 29.89%) harbored PKS I, PKS II, and NRPS genes in their genomes. Nevertheless, their bioactivity is independent of BGCs in this study. Our findings highlighted the antimicrobial, immunosuppressive, and anticancer potential of mangrove rhizosphere Actinobacteria from Hainan Island and the biosynthetic prospects of exploiting the corresponding bioactive natural product.

Diversity of endophytic fungi in Coptis chinensis Franch. and their activity against methicillin-resistant Staphylococcus aureus

This study aimed at investigating the diversity of endophytic fungi from Coptis chinensis and their activity against methicillin-resistant Staphylococcus aureus (MRSA). Seventy-nine fungal isolates obtained from C. chinensis were identified to belong to 27 species based on morphological features and internal transcript spacer (ITS) gene sequencing analysis. Comparing relative frequency values, the most frequent genera were Colletotrichum and Fusarium, while most frequent species were C. gloeosporioides and F. avenaceum. Analysis of diversity indices indicated that C. chinensis harbored abundant fungal resources. Methanol extracts of fungal endophyte cultures were evaluated for antibacterial activity against S. aureus ATCC 25923 and two other MRSA clinical strains. Nine of 27 endophytic fungi exhibited inhibitory activities against S. aureus ATCC 25923. Among them, Paraboeremia litseae HL-17, Fusarium sp. HL-23, and Fusarium sp. HL-27 exhibited obvious inhibition against the three S. aureus strains. Our findings suggest that the endophytic fungi in C. chinensis have a high diversity and an obvious tissue specificity, and could be of potential interest in screening anti-MRSA agents. To the best of our knowledge, this is the first report on the diversity and anti-MRSA activity of fungal endophytes from C. chinensis.

Desert soil fungi isolated from Saudi Arabia: cultivable fungal community and biochemical production

Desert soils harbor fungi that have survived under highly stressed conditions of high temperature and little available moisture. This study was designed to survey the communities of cultivable fungi in the desert soils of the Arabian Peninsula and to screen the fungi for the potentially valuable antioxidants (flavonoids, phenols, saponins, steroids, tannins, terpenoids, and alkaloids) and enzymes (cellulase, laccase, lipase, protease, amylase, and chitinase). Desert soil was sampled at 30 localities representing different areas of Saudi Arabia and studied for physico-chemical soil properties. Five types of soil texture (sand, loamy sand, sandy loam, silty loam, and sandy clay loam) were observed. A total of 25 saprotrophic species was identified molecularly from 68 isolates. Our survey revealed 13 culturable fungal species that have not been reported previously from Arabian desert soils and six more species not reported from Saudi Arabian desert soils. The most commonly recorded genera were Aspergillus (isolated from 20 localities) and Penicillium (6 localities). The measurements of biochemicals revealed that antioxidants were produced by 49 and enzymes by 52 isolates; only six isolates did not produce any biochemicals. The highest biochemical activity was observed for the isolates Fusarium brachygibbosum and A. phoenicis. Other active isolates were A. proliferans and P. chrysogenum. The same species, for instance, A. niger had isolates of both high and low biochemical activities. Principal component analysis gave a tentative indication of a relationship between the biochemical activity of fungi isolated from soil and soil texture variables namely the content of silt, clay and sand. However, any generalizable relation between soil properties and fungal biochemical activities cannot be suggested. Each fungal isolate is probable to produce several antioxidants and enzymes, as shown by the correlation within the compound groups. Desert soil warrants further research as a promising source of biochemicals.