Endophytic actinobacteria of medicinal plant Aloe vera: Isolation, antimicrobial, antioxidant, cytotoxicity assays and taxonomic study

New opportunities and perspectives on biosynthesis and bioactivities of secondary metabolites from Aloe vera

Historically, the genus Aloe has been an indispensable part of both traditional and modern medicine. Decades of intensive research have unveiled the major bioactive secondary metabolites of this plant. Recent pandemic outbreaks have revitalized curiosity in aloe metabolites, as they have proven pharmacokinetic profiles and repurposable chemical space. However, the structural complexity of these metabolites has hindered scientific advances in the chemical synthesis of these compounds. Multi-omics research interventions have transformed aloe research by providing insights into the biosynthesis of many of these compounds, for example, aloesone, aloenin, noreugenin, aloin, saponins, and carotenoids. Here, we summarize the biological activities of major aloe secondary metabolites with a focus on their mechanism of action. We also highlight the recent advances in decoding the aloe metabolite biosynthetic pathways and enzymatic machinery linked with these pathways. Proof-of-concept studies on in vitro, whole-cell, and microbial synthesis of aloe compounds have also been briefed. Research initiatives on the structural modification of various aloe metabolites to expand their chemical space and activity are detailed. Further, the technological limitations, patent status, and prospects of aloe secondary metabolites in biomedicine have been discussed.

Bioprospecting of endophytic actinobacterium associated with Aloe ferox mill for antibacterial activity

BACKGROUND

The emergence of drug resistance among pathogens has resulted in renewed interest in bioprospecting for natural microbial products.

METHODS

This study aimed to bioprospecting endophytic actinobacterium associated with Aloe ferox Mill for its antibacterial activity. Endophytic actinomycetes were isolated from the gel of A. ferox Mill by surface sterilization technique using actinomycete isolation agar. The isolate with a promising antibacterial activity was identified using 16S rRNA sequence analysis. The minimum inhibitory concentration (MIC) of the extract was assessed by the micro-dilution method and its effect on the respiratory chain dehydrogenase (RCD) activity was ascertained by the iodonitrotetrazolium chloride (INT) assay. Fourier transform-infrared spectrophotometer (FTIR) and gas chromatography-mass spectrophotometry (GC-MS) were employed to identify functional groups and the chemical constituents, respectively.

RESULTS

The actinobacterium was found to be Streptomyces olivaceus CP016795.1. Its extract displayed noteworthy antibacterial activity (MIC ≤1 mg/mL) against Staphylococcus aureus (ATCC 25925), Bacillus cereus (ATCC 10102), and Escherichia coli (ATCC 25922); and showed an inhibitory effect on the RCD activity. FTIR spectrum displayed hydroxyl, amine, and aromatic groups, and the GC-MS revealed 5-Hydroxymethylfurfural as the main constituent (19.47%).

CONCLUSIONS

S. olivaceus CP016795.1 can serve as a potential source of effective antibacterial compounds.

A Review on Medicinal Plants Having Anticancer Properties of Northeast India and Associated Endophytic Microbes and their Future in Medicinal Science

Human beings are affected by different diseases and suffer to different extents. Cancer is one of the major human disease and millions of people suffered from cancer and end their lives every year. Peoples are dependent on herbal medicines since prehistoric time especially from developing countries. It is very common to have different side effects of modern synthetic medicines; hence now-a-days importance of herbal medicines due to no or least side effects increases all parts of the world. But the major problems of using herbal medicines are that plants can produce very limited amount of medicinally important bioactive metabolites and they have very long growth periods. Therefore endophytes are the excellent alternative of plant derived metabolites. Endophytic microbes can synthesize exactly same type of metabolites as the plant produces. North East India is a treasure of plant resources; various types of medicinal plants are present in this region. Different types of indigenous tribes are inhabited in this region who used different plants in traditional system for treating various disease. But with increasing demand it is sometimes not sufficient to manage the demand of medicines, therefore for massive production endophytic study is crucial. In spite of having huge plant resources very limited endophytic studies are observed in this region. In this review, we studied different plants with their endophytes of NE India showing anticancer properties.

Diversity and communities of culturable endophytic fungi from the root holoparasite Balanophora polyandra Griff. and their antibacterial and antioxidant activities

Purpose

Balanophora polyandra Griff. is a holoparasitic medicinal plant that produces compounds with antibacterial and antioxidant activities. Plant endophytic fungi are an abundant reservoir of bioactive metabolites for medicinal exploitation, and an increasing number of novel bioactive compounds are being isolated from endophytic fungi. The present study investigated the diversity of culturable endophytic fungi from the roots of holoparasite B. polyandra to explore active strains and metabolites. In addition, the antibacterial and antioxidant activities of 22 strains cultured from B. polyandra were also evaluated.

Methods

The endophytic fungi were identified according to their colony morphology and ITS-5.8S rDNA sequencing. TLC-MTT-Bioautography assays and DPPH radical scavenging assays were employed to assess the antibacterial and antioxidant activities of ethyl acetate extracts of the endophytic fungi.

Results

One hundred and twenty-five endophytic strains were isolated from the roots of B. polyandra, including 70 from female samples and 55 from male samples. Of them, twenty-two distinct isolates representing 15 genera and 22 species based on their ITS-rDNA genomic sequence were successfully identified from female and male samples of B. polyandra. The genus Calonectria was the most prevalent genus, with a CF% of 18.3, followed by the genera Clonostachys and Botryosphaeria, with CF% values of 13.4 and 10.0, respectively. Interestingly, the fungal extracts exhibited broad-spectrum antibacterial activities against gram-positive and gram-negative bacteria, as well as potential antioxidant activities with IC50 values ranging from 0.45 to 6.90 mg/mL. Among them, endophytes Bpf-10 (Diaporthe sp.) and Bpf-11 (Botryosphaeria sp.) showed the strongest biological activities and more abundant secondary metabolites.

Conclusions

This study reported the diversity of endophytic fungi from the roots of B. polyandra and the antibacterial and antioxidant activities of the crude extracts for the first time. The results revealed that B. polyandra contains diverse culturable endophytic fungi that potentially produce natural antibacterial and antioxidant compounds with great value to the agriculture and pharmaceutical industries.

Biocompatible CuInS2 Nanoparticles as Potential Antimicrobial, Antioxidant, and Cytotoxic Agents

A simple hydrothermal route is employed to synthesize pure copper indium disulfide (CIS) and CIS nanoparticles (NPs) mediated by various natural plant extracts. The plant extracts used to mediate are Azadirachta indica (neem), Ocimum sanctum (basil), Cocos nucifera (coconut), Aloe vera (aloe), and Curcuma longa (turmeric). The tetragonal unit cell structure of as-synthesized NPs is confirmed by X-ray diffraction. The analysis by energy-dispersive X-rays shows that all the samples are near-stoichiometric. The morphologies of the NPs are confirmed by high-resolution scanning and transmission modes of electron microscopy. The thermal stability of the synthesized NPs is determined by thermogravimetric analysis. The optical energy band gap is determined from the absorption spectra using Tauc's equation. The antimicrobial activity analysis and the estimation of the minimum inhibitory concentration (MIC) value of the samples are performed for Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Enterobacter aerogenes, and Staphylococcus aureus pathogens. It shows that the aloe-mediated CIS NPs possess a broad inhibitory spectrum. The best inhibitory effect is observed against S. aureus, whereas the least effect was exhibited against P. vulgaris. The least MIC value is found for aloe-mediated CIS NPs (0.300 mg/mL) against S. aureus, P. aeruginosa, and E. aerogenes, along with basil-mediated NPs against E. coli. The antioxidant activity study showed that the IC₅₀ value to inhibit the scavenging activity is maximum for the control (vitamin C) and minimum for pure CIS NPs. The in vivo cytotoxicity study using brine shrimp eggs shows that the pure CIS NPs are more lethal to brine shrimp than the natural extract-mediated CIS NPs. The in vitro cytotoxicity study using the human lung carcinoma cell line (A549) shows that the IC₅₀ value of turmeric extract-mediated CIS NPs is minimum (15.62 ± 1.58 μg/mL). This observation reveals that turmeric extract-mediated CIS NPs are the most potent in terms of cytotoxicity toward the A549 cell line.

Streptomyces-Derived Metabolites with Potential Photoprotective Properties-A Systematic Literature Review and Meta-Analysis on the Reported Chemodiversity

Sun overexposure is associated with the development of diseases that primarily affect the skin, which can lead to skin cancer. Among the main measures of photoprotection is the use of sunscreens. However, there is currently concern about the reported harmful effects to both humans and the environment due to several of the sunscreen ingredients available on the market. For this reason, the search for and development of new agents with photoprotective properties is required. In searching for these metabolites, researchers have turned their attention to microbial sources, especially the microbiota in unusual hostile environments. Among the diverse microorganisms available in nature, Actinobacteria and specifically Streptomyces, have been shown to be a source of metabolites with various biological activities of interest, such as antimicrobial, antitumor and immunomodulator activities. Herein, we present the results of a systematic review of the literature in which Streptomyces isolates were studied as a source of compounds with photoprotective properties. A meta-analysis of the structure-property and structure-activity relationships of those metabolites identified in the qualitative analysis phase was also carried out. These findings indicate that Streptomyces are a source of metabolites with potential applications in the development of new, safe and more eco-friendly sunscreens.

Antioxidant Activities of Streptomyces sp. strain MUSC 14 from Mangrove Forest Soil in Malaysia

The mangrove ecosystem of Malaysia remains yet to be fully explored for potential microbes that produce biologically active metabolites. In the present study, a mangrove-derived Streptomyces sp. strain MUSC 14 previously isolated from the state of Pahang, Malaysia Peninsula, was studied for its potential in producing antioxidant metabolites. The identity of Streptomyces sp. strain MUSC14 was consistent with the genotypic and phenotypic characteristics of the Streptomyces genus. The antioxidant potential of Streptomyces sp. strain MUSC 14 was determined through screening of its methanolic extract against sets of antioxidant assays. The results were indicative of Streptomyces sp. strain MUSC 14 displaying strong antioxidant activity against ABTS, DPPH free radicals and metal chelating activity of 62.71 ± 3.30%, 24.71 ± 2.22%, and 55.82 ± 2.35%, respectively. The result of ferric reducing activity measured in terms of dose was equivalent to 2.35–2.45 μg of positive control ascorbic acid. Furthermore, there was a high correlation between the total phenolic content and the antioxidant activities with r = 0.979, r = 0.858, and r = 0.983 representing ABTS, DPPH, and metal chelation, respectively. Overall, the present study suggests that Streptomyces sp. strain MUSC 14 from mangrove forest soil has potential to produce antioxidant metabolites that can be further exploited for therapeutic application.