Over a long period of time, humans have explored many natural resources looking for remedies of various ailments. Traditional medicines have played an intrinsic role in human life for thousands of years, with people depending on medicinal plants and their products as dietary supplements as well as using them therapeutically for treatment of chronic disorders, such as cancer, malaria, diabetes, arthritis, inflammation, and liver and cardiac disorders. However, plant resources are not sufficient for treatment of recently emerging diseases. In addition, the seasonal availability and other political factors put constrains on some rare plant species. The actual breakthrough in drug discovery came concurrently with the discovery of penicillin from Penicillium notatum in 1929. This discovery dramatically changed the research of natural products and positioned microbial natural products as one of the most important clues in drug discovery due to availability, variability, great biodiversity, unique structures, and the bioactivities produced. The number of commercially available therapeutically active compounds from microbial sources to date exceeds those discovered from other sources. In this review, we introduce a short history of microbial drug discovery as well as certain features and recent research approaches, specifying the microbial origin, their featured molecules, and the diversity of the producing species. Moreover, we discuss some bioactivities as well as new approaches and trends in research in this field.

In spite of great developments in the agricultural field and plant productivity in the last decades, the concern about the control of agricultural pests is still continuous. However, pest management is expected to have more effects from nanomaterials by providing innovative solutions. The current study confirms the biotransformation of copper nanoparticles (CuNPs) using a cell-free culture extract of metal copper-resistant bacteria Pseudomonas fluorescens MAL2, which was isolated from heavy metal-contaminated soils collected from Sharqia Governorate, Egypt. The local screened bacterial isolate, Pseudomonas fluorescens MAL2, is similar to Pseudomonas fluorescens DSM 12442T DSM. After optimization of growth conditions, F-Base medium was found to be the best medium and pH 7, temperature 35 °C, concentration of CuSO₄·5H₂O 300 ppm, 10 mL supernatant: 40 mL CuSO₄·5H₂O (300 ppm), and reaction time 90 min were recorded as the best growth conditions to the fabrication of CuNPs. The formed CuNPs were characterized using initially visual observation of the change in the color of the reaction mixture from blue color to the dark green as an indication of CuNPs biotransformation. Then, UV–Vis spectroscopy showed a maximum absorption at 610 nm under the optimum conditions performed. Transmission Electron Microscopy (TEM) revealed the formation of spherical aspect with size ranges from 10:70 nm; moreover, Energy Dispersive X-ray spectroscopy (EDX) indicated the presence of CuNPs and other elements. In addition, the presence of alcohols, phenols, alkenes, and amines is confirmed by Fourier-Transform Infrared spectroscopy (FTIR) spectroscopy analysis. Dynamic Light Scattering (DLS) supported that the Zeta-average size of nanoparticle was 48.07 with 0.227 PdI value. The Zeta potential showed −26.00mV with a single peak. The biosynthesized CuNPs (Bio CuNPs) showed toxicity against the stored grain pest (Tribolium castaneum), where LC₅₀ value was 37 ppm after 5 days of treatment. However, the negligible effect was observed with chemical synthesis of CuNPs (Ch CuNPs) at the same concentration. The results suggest that Bio CuNPs could be used not only as a biocontrol agent, but also as an ecofriendly and inexpensive approach for controlling the stored grain pests.

The adverse influences of elevated ambient temperatures during the summer season on the rabbit industry have received increased global attention. Therefore, this study intended to compare the potential effects of nano-selenium (nano-Se) synthesized by biological (BIO) and chemical (CH) methods on growth performance, carcass variables, serum metabolites, and inflammatory cytokines responses of growing rabbits in the summer season. Two hundred and fifty weaned rabbits (males, 35 days of age) were randomly divided into five treatment groups of 50 rabbits each (each group had five replicates with ten male rabbits). Treatment groups were fed a control diet and four controlled diets supplemented with nano-Se synthesized by biological method (BIO25 and BIO50, with a 25 and 50 mg of nano-Se/kg diet, respectively) and chemical method (CH25 and CH50, with a 25 and 50 mg of nano-Se/kg diet, respectively) for eight weeks. During 11 to 13 weeks of age, a gradual enhancement in live body weight (LBW), feed intake (FI) and feed conversion ratio (FCR) was noticed with BIO25 and BIO50 treatments compared to those in the other groups. The carcass percentage was significantly higher (p < 0.01) for animals fed with BIO25 than the other groups. The other organ functions were significantly higher (p < 0.01) in heat-stressed groups compared to that of nano-Se groups. Increasing the level of only BIO from a 25 to a 50 mg/kg diet gave more improvement in the studied parameters. Additionally, the concentrations of serum urea, triglycerides (TG), and glutamyl transferase (GGT) were lower (p < 0.01) in both treated and untreated groups. Likewise, the supplementation with nano-Se (BIO25, BIO50, or CH25) significantly improved the antioxidant indices and inflammatory cytokines responses as indicated from serum metabolites. Based on the study results, nano-Se especially synthesized by the biological method at diet levels of 25 or 50 mg/kg improved the growth performance, kidney and liver functions, carcass traits, antioxidants indices, and inflammatory cytokines of growing rabbits during thermal stress.