Molecular characterization of an endophytic Phomopsisliquidambaris CBR-15 from Cryptolepis buchanani Roem. and impact of culture media on biosynthesis of antimicrobial metabolites

Evaluation of the Antibacterial Activity of Crude Extracts Obtained From Cultivation of Native Endophytic Fungi Belonging to a Tropical Montane Rainforest in Colombia

Bioactive secondary metabolite production from endophytic fungi has gained a recurring research focus in recent decades as these microorganisms represent an unexplored biological niche for their diverse biotechnological potential. Despite this focus, studies involving tropical endophytes remain scarce, particularly those isolated from medicinal plants of these ecosystems. In addition, the state of the art of the pharmaceutical industry has experienced stagnation in the past 30years, which has pushed pathogenic infections to get one step ahead, resulting in the development of resistance to existing treatments. Here, five fungal endophytes were isolated from the medicinal plant Otoba gracilipes (Myristicaceae), which corresponded to the genera Xylaria and Diaporthe, and screened to demonstrate the promissory potential of these microorganisms for producing bioactive secondary metabolites with broad-spectrum antibacterial activities. Thus, the evaluation of crude organic extracts obtained from the mycelia and exhaust medium allowed the elucidation of Xylaria sp. and Diaporthe endophytica potential toward providing crude extracellular extracts with promising bioactivities against reference strains of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923), according to the determined half-maximum inhibitory concentration (IC₅₀) with values down to 3.91 and 10.50mg/ml against each pathogen, respectively. Follow-up studies provided insights into the polarity nature of bioactive compounds in the crude extracts through bioactivity guided fractionation using a polymeric resin absorbent alternative extraction procedure. In addition, evaluation of the co-culturing methods demonstrated how this strategy can enhance endophytes biosynthetic capacity and improve their antibacterial potential with a 10-fold decrease in the IC₅₀ values against both pathogens compared to the obtained values in the preliminary evaluations of Xylaria sp. and D. endophytica crude extracts. These results support the potential of Colombian native biodiversity to provide new approaches concerning the global emergence of antibiotics resistance and future production of undiscovered compounds different from the currently used antibiotics classes and simultaneously call for the value of preserving native habitats due to their promising ecosystemic applications in the biotechnological and pharmaceutical industries.

Evaluation of bone healing activity of Cissus quadrangularis (Linn), Cryptolepis buchanani, and Sardinella longiceps in Wistar rats

Background

The object of the present study is to evaluate the effect of alcoholic extracts of Cissus quadrangularis (CQ), Cryptolepis buchanani (CB), and Sardinella longiceps (SL) either alone or in the combination (100 mg/kg) in the management of femur bone healing of Wistar albino rats for 8 weeks. After the period of treatment, femur bones were examined by using biochemical, radiographical, and histopathological studies.

Result

Biochemical evaluation results reveal that there is a steep increase of serum calcium level in the experimental animals during the entire period of treatment which led to an adequate supply of serum calcium to the fractured bone for healing and increases the thickness of the femur bones soon compared to control group. It had been estimated by a calibrated ocular micrometer. Radiographical images of the bones also disclose that the complete bridging of fractured bone occurred in the experimental animals after the treatment of natural compound extracts. In addition to that, all the organs of animals were safe in the experimental animals during the entire study.

Conclusion

The present study strongly recommended that these ethanolic extracts (CQCBSL) either alone or in the combination restoring the strength of the bone and reduced bone repairing period due to the rich content of calcium and other natural phytochemicals presents with them.

Graphical abstract

Annulohypoxylon sp. strain MUS1, an endophytic fungus isolated from Taxus wallichiana Zucc., produces taxol and other bioactive metabolites

The current study focuses on the isolation and in vitro characterization of bioactive metabolites produced by endophytic fungi isolated from the Himalayan yew (Taxus wallichiana Zucc.). The endophytic fungi were isolated on artificial media from inner tissues of bark and needles. Antimicrobial and antioxidant activity, along with total phenolic- and flavonoid-content assays were used in the evaluation of bioactivity of the fermented crude extracts. The ability of the endophytes to produce the anticancer compound Taxol was also analyzed using thin-layer chromatography (TLC) and reverse-phase high-performance liquid chromatography (RP-HPLC). A total of 16 fungal morphotypes were obtained from asymptomatic inner tissues of the bark and needles of T. wallichiana. Among the 16 isolates, the ethyl acetate (EA) fraction of isolate MUS1, showed antibacterial and antifungal activity against all test-pathogens used (Streptococcus faecalis ATCC 19433, Staphylococcus aureus ATCC 12600, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, Salmonella enterica ATCC 13076, Pseudomonas aeruginosa ATCC 27853, and Candida albicans). MUS1 showed significant inhibition against Pseudomonas aeruginosa ATCC 27853 (minimum inhibitory concentration (MIC): 250 µg/ml) and the pathogenic yeast, Candida albicans (MIC: 125 µg/ml). Antioxidant activity, total phenolic, and total flavonoid content as well as in vitro Taxol production were evaluated for EA fraction of isolate MUS1. Antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. At a concentration of 100 µg/ml, the % DPPH radical scavenging activity was 83.15 ± 0.40, 81.62 ± 0.11, and 62.36 ± 0.29, for ascorbic acid, butylated hydroxytoluene (BHT), and the EA fraction of MUS1, respectively. The DPPH-Half maximal inhibitory concentration (DPPH-IC₅₀) value for the EA fraction was 81.52 ± 0.23 µg/ml, compared to BHT (62.87 ± 0.08 µg/ml) and ascorbic acid (56.15 ± 0.19 µg/ml). The total phenolic and flavonoid content in the EA fraction were 16.90 ± 0.075 µg gallic acid equivalent (GAE) and 11.59 ± 0.148 µg rutin equivalent (RE), per mg of dry crude extract, respectively. TLC and RP-HPLC analysis showed that the isolate MUS1 also produces Taxol (282.05 µg/l of fermentation broth). Isolate MUS1 was identified as Annulohypoxylon sp. by internal transcribed spacer (ITS) sequencing. Having the ability to produce antimicrobial and antioxidant metabolites, as well as the anticancer compound Taxol, makes Annulohypoxylon sp. strain MUS1, a promising candidate for further study of naturally occurring bioactive metabolites.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02693-z.

Molecular profiling of endophytic Streptomyces cavourensis MH16 inhabiting Millingtonia hortensis Linn. and influence of different culture media on biosynthesis of antimicrobial metabolites

Endophytic actinomycetes, a prolific source of natural products, are well known for their diverse metabolic versatility, and their association with medicinal plants and antimicrobial potential are well worth exploring. We isolated and identified the Streptomyces cavourensis strain MH16 inhabiting the tree Millingtonia hortensis Linn. using phylogenetic analysis based on a 16S rRNA molecular approach. We used the disc diffusion method to evaluate the impact of differences in the compositions of the media on the production of secondary metabolites from strain MH16. The production of antimicrobial metabolites was determined by the observation of inhibition zones on intensive bands when using a TLC-bioautography assay. Biosynthesis of secondary metabolites was optimal when the strain MH16 was cultured in ISP-2 medium as depicted by a zone of inhibition. Strain MH16 effectively inhibited methicillin-resistant Staphylococcus aureus, Escherichia coli, Candida albicans, and other multi drug-resistant pathogens. The minimum inhibitory concentration of the antimicrobial metabolites was 25-100 μg mL^-1. The study manifests the optimization and utilization of different fermentation media which best suits for increased production of the secondary metabolites from Streptomyces cavourensis. This research suggests that the antimicrobial metabolites of strain MH16 found in M. hortensis has great potential for the biodiscovery of new anti-infective drugs against a wide range of multidrug-resistant pathogens.

Chemogenomics driven discovery of endogenous polyketide anti-infective compounds from endosymbiotic Emericella variecolor CLB38 and their RNA secondary structure analysis

In the postgenomic era, a new strategy for chemical dereplication of polyketide anti-infective drugs requires novel genomics and chromatographic strategies. An endosymbiotic fungal strain CLB38 was isolated from the root tissue of Combretum latifolium Blume (Combretaceae) which was collected from the Western Ghats of India. The isolate CLB38 was then identified as Emericella variecolor by its characteristic stellate ascospores culture morphology and molecular analysis of ITS nuclear rDNA and intervening 5.8S rRNA gene sequence. ITS2 RNA secondary structure modeling clearly distinguished fungal endosymbiont E. variecolor CLB38 with other lifestyles in the same monophyletic clade. Ethyl acetate fraction of CLB38 explored a broad spectrum of antimicrobial activity against multidrug resistant pathogens. Biosynthetic PKS type-I gene and chromatographic approach afford two polyketide antimicrobial compounds which identified as evariquinone and isoindolones derivative emerimidine A. MIC of purified compounds against test microorganisms ranged between 3.12 μg/ml and 12.5 μg/ml. This research highlights the utility of E. variecolor CLB38 as an anticipate source for anti-infective polyketide metabolites evariquinone and emerimidine A to combat multidrug resistant microorganisms. Here we demonstrates a chemogenomics strategy via the feasibility of PKS type-I gene and chromatographic approach as a proficient method for the rapid prediction and discovery of new polyketides compounds from fungal endosymbionts.

Biomimetic Synthesis of Silver Nanoparticles Using Endosymbiotic Bacterium Inhabiting Euphorbia hirta L. and Their Bactericidal Potential

The present investigation aims to evaluate biomimetic synthesis of silver nanoparticles using endophytic bacterium EH 419 inhabiting Euphorbia hirta L. The synthesized nanoparticles were initially confirmed with change in color from the reaction mixture to brown indicating the synthesis of nanoparticles. Further confirmation was achieved with the characteristic absorption peak at 440 nm using UV-Visible spectroscopy. The synthesized silver nanoparticles were subjected to biophysical characterization using hyphenated techniques. The possible role of biomolecules in mediating the synthesis was depicted with FTIR analysis. Further crystalline nature of synthesized nanoparticles was confirmed using X-ray diffraction (XRD) with prominent diffraction peaks at 2θ which can be indexed to the (111), (200), (220), and (311) reflections of face centered cubic structure (fcc) of metallic silver. Transmission electron microscopy (TEM) revealed morphological characteristics of synthesized silver nanoparticles to be polydisperse in nature with size ranging from 10 to 60 nm and different morphological characteristics such as spherical, oval, hexagonal, and cubic shapes. Further silver nanoparticles exhibited bactericidal activity against panel of significant pathogenic bacteria among which Pseudomonas aeruginosa was most sensitive compared to other pathogens. To the best of our knowledge, present study forms first report of bacterial endophyte inhabiting Euphorbia hirta L. in mediating synthesizing silver nanoparticles.

Molecular profiling and antimicrobial potential of endophytic Gliomastix polychroma CLB32 inhabiting Combretum latifolium Blume

Fungal endophytes as a source of bioactive metabolites have led to the development of pharmaceutical products finding new applications. In a survey of endophytic fungal biodiversity, an antimicrobial endophytic strain CLB32 was isolated from the leaf of Combretum latifolium Blume (Combretaceae) from the Western Ghats of Southern India. CLB32 was then identified as Gliomastix polychroma (KR704576) by morphological and phylogenetic analysis based on internal transcribed spacer (ITS) nuclear rDNA and intervening 5.8S rRNA gene. CLB32 here constituted the first report on incidence of endophytic fungi from C. latifolium Blume. Ethyl acetate fraction of strain CLB32 was evaluated for antimicrobial activity by disc diffusion assay. Secondary metabolites produced effectively inhibited methicillin-resistant Staphylococcus aureus (18.33 ± 0.33 mm), Pseudomonas aeruginosa (14.66 ± 0.33 mm) and Candida albicans (14.00 ± 0.57 mm). Biosynthesis of these antimicrobial compounds was detected by analytical TLC-bioautography method as depicted by zone of inhibition on intensive the band. These findings suggest that G. polychroma CLB32, as a producer of natural antimicrobial drugs, could help to combat against multidrug-resistant infections and also provide baseline information for industrial applications.

Bacterial Endo-Symbiont Inhabiting Tridax procumbens L. and Their Antimicrobial Potential

Bacterial symbionts inhabiting Tridax procumbens L. were screened for antimicrobial potential with the aim to isolate potent bacteria bearing significant activity against test pathogens. The selected isolate was subjected to large scale fermentation to extract antimicrobial metabolite. The organic phase was reduced under vacuum pressure and crude ethyl acetate extract (10 mg/mL) was evaluated for antimicrobial activity against panel of test pathogens. The antibacterial activity was measured as a zone of inhibition and compared with standard antibiotics, gentamicin and tetracycline. Similarly, antifungal activity was compared with miconazole and bavistin. Significant activity was conferred against Shigella flexneri (MTCC 731) with 27±1.5 mm zone across the disc. Partially, purification of antimicrobial metabolite with TLC-bioautography and HPLC resulted in active fraction bearing activity at Rf 0.65 and eluting between 4 and 5 retention times. The obtained results are promising enough for future purification and characterization of antimicrobial metabolite. Thus, the study attributes to the growing knowledge on endophytes as one of the rich sources of antimicrobial potentials.