Context: Streptomyces species are prolific sources of bioactive secondary metabolites known especially for their antimicrobial and anticancer activities.Objective: This study sought to isolate and characterize antioxidant molecules biosynthesized by Streptomyces sp. KTM18. The antioxidant potential of an isolated compound and its toxicity were accessed. Materials and methods: The compound was purified using bioassay-guided chromatography techniques. Nuclear magnetic resonance (NMR) experiments were carried out for structure elucidation. The antioxidant potential of the isolated compound was determined using DPPH free radical scavenging assay. The toxicity of the isolated compound was measured using a brine shrimp lethality (BSL) assay. Results: Ethyl acetate extract of Streptomyces sp. KTM18 showed more than 90% inhibition of DPPH free radical at 50 mg/mL of the test concentration. These data were the strongest among 13 Streptomyces isolates (KTM12-KTM24). The active molecule was isolated and characterized as maculosin (molecular formula, C 14 H 16 N 2 O 3 as determined by the [M þ H] þ peak at 261.1259). The DPPH free radical scavenging activity of pure maculosin was higher (IC 50 , 2.16 ± 0.05 mg/mL) than that of commercial butylated hydroxyanisole (BHA) (IC 50 , 4.8 ± 0.05 mg/mL). No toxicity was observed for maculosin (LD 50 , <128 mg/mL) in brine shrimp lethality assay (BSLA) up to the compound's antioxidant activity (IC 50 ) concentration range. The commercial standard, berberine chloride, showed toxicity in BSLA with an LD 50 value of 8.63 ± 0.15 mg/mL. Conclusions: Maculosin may be a leading drug candidate in various cosmetic and therapeutic applications owing to its strong antioxidant and non-toxic properties.

Background: Guava (Psidium guajava Linn.) has been traditionally used in the treatment of a wide range of diseases due to its rich content of secondary metabolites. This study was aimed to evaluate the effect of altitude and solvent systems on guava leaves crude extract’s phenolics and flavonoid content, antioxidant, antimicrobial, and its toxicity nature.Methods: Guava leaves were collected from three different geographical locations of Nepal while solvents with an increasing polarity index were used for extraction. The yield percentage of extracts was calculated. Total Phenolic Content, Total Flavonoid Content, and antioxidant activity were determined by the Folin-Ciocalteu method, Aluminium chloride colorimetric method, and DPPH (2,2’-Diphenyl-1-picrylhydrazyl) assay respectively. The quantification of fisetin and quercetin was performed using the HPLC with method validation. The antimicrobial activity of the extracts was tested against bacteria and fungus isolated from spoiled fruits and vegetables and identified through 16s and 18s rRNA sequencing. Finally, Brine Shrimp Lethality Assay (BSLA) was used for testing the toxicity of the extracts.Results: The phenolic and total flavonoid content was found to be higher in ethanol extract (331.84 mg GAE/g) and methanol extract (95.53 mg QE/g) from Kuleshwor respectively. Water extract of guava leaves from Kuleshwor (WGK) did not show significantly different antioxidant activity when compared to methanol and ethanol extracts. Fisetin and quercetin were higher in WGK (1.176 mg/100 g) and (10.967 mg/100 g) dry extract weight respectively. Antibacterial activity against food spoilage bacteria was dose dependent and found to be highest for all the extracts from different solvents and altitude at higher concentrations (80 mg/ml). Similarly, methanol and ethanol guava extracts from all locations showed antifungal activity against Geotrichum candidum RIBB-SCM43 and Geotrichum candidum RIBB-SCM44. WGK was found to be non-toxic.Conclusion: Our study concludes that the antioxidant and antimicrobial activity of WGK was found to be simlar with that of methanol and ethanol extracts of Bishnupur Katti and Mahajidiya. These results suggest the possibility of using water as a sustainable solvent to extract natural antioxidant and antimicrobial compounds which can further be used as natural preservatives to extend the shelf life of fruits and vegetables.

Background Guava (Psidium guajava Linn.) has been traditionally used in the treatment of a wide range of diseases due to its rich content of secondary metabolites. Aim This study was aimed to evaluate the effect of altitude and solvent systems on guava leaves crude extract’s phenolics and flavonoid content, antioxidant, antimicrobial, and toxicity nature. Methods Guava leaves were collected from three different geographical locations in Nepal while solvents with an increasing polarity index were used for extraction. The yield percentage of extracts was calculated. Total Phenolic Content, Total Flavonoid Content, and antioxidant activity were determined by the Folin-Ciocalteu method, Aluminium chloride colorimetric method, and DPPH (2,2′-Diphenyl-1-picrylhydrazyl) assay respectively. The quantification of fisetin and quercetin was performed using the HPLC with method validation. The antimicrobial activity of the extracts was tested against bacteria and fungus isolated from spoiled fruits and vegetables and identified through 16s and 18s rRNA sequencing. Finally, Brine Shrimp Lethality Assay (BSLA) was used for testing the toxicity of the extracts. Results The phenolic and total flavonoid content was found to be higher in ethanol extract (331.84 mg GAE/g dry extract) and methanol extract (95.53 mg QE/g dry extract) from Kuleshwor respectively. Water extract of guava leaves from Kuleshwor (WGK) did not show significantly different antioxidant activity when compared to methanol and ethanol extracts. Fisetin and quercetin were higher in WGK (1.176 mg/100 g) and (10.967 mg/100 g) dry extract weight respectively. Antibacterial activity against food spoilage bacteria was dose-dependent and found to be highest for all the extracts from different solvents and altitudes at higher concentrations (80 mg/ml). Similarly, methanol and ethanol guava extracts from all locations showed antifungal activity against Geotrichum candidum RIBB-SCM43 and Geotrichum candidum RIBB-SCM44. WGK was found to be non-toxic. Conclusion Our study concludes that the antioxidant and antimicrobial activity of WGK was found to be similar statistically to that of methanol and ethanol extracts of Bishnupur Katti and Mahajidiya. These results suggest the possibility of using water as a sustainable solvent to extract natural antioxidant and antimicrobial compounds which can further be used as natural preservatives to extend the shelf life of fruits and vegetables.