Actinobacteria are prolific producers of thousands of biologically active natural compounds with diverse activities. More than half of these bioactive compounds have been isolated from members belonging to actinobacteria. Recently, rare actinobacteria existing at different environmental settings such as high altitudes, volcanic areas, and marine environment have attracted attention. It has been speculated that physiological or biochemical pressures under such harsh environmental conditions can lead to the production of diversified natural compounds. Hence, marine environment has been focused for the discovery of novel natural products with biological potency. Many novel and promising bioactive compounds with versatile medicinal, industrial, or agricultural uses have been isolated and characterized. The natural compounds cannot be directly used as drug or other purposes, so they are structurally modified and diversified to ameliorate their biological or chemical properties. Versatile synthetic biological tools, metabolic engineering techniques, and chemical synthesis platform can be used to assist such structural modification. This review summarizes the latest studies on marine rare actinobacteria and their natural products with focus on recent approaches for structural and functional diversification of such microbial chemicals for attaining better applications.

An Ag-loaded BiVO ₄ visible-light-driven photocatalyst was synthesized by the microwave hydrothermal method followed by photodeposition. The photocatalytic performance of the synthesized samples was evaluated on a mixed dye (methylene blue and rhodamine B), as well as bisphenol A in aqueous solution. Similarly, the disinfection activities of synthesized samples towards the Gram-negative Escherichia coli ( E. coli ) in a model cell were investigated under irradiation with visible light ( λ ≥ 420 nm). The synthesized samples have monoclinic scheelite structure. Photocatalytic results showed that all Ag-loaded BiVO ₄ samples exhibited greater degradation and a higher mineralization rate than the pure BiVO ₄ , probably due to the presence of surface plasmon absorption that arises due to the loading of Ag on the BiVO ₄ surface. The optimum Ag loading of 5 wt% has the highest photocatalytic performance and greatest stability with pseudo-first-order rate constants of 0.031 min ⁻¹ and 0.023 min ⁻¹ for the degradation of methylene blue and rhodamine B respectively in a mixture with an equal volume and concentration of each dye. The photocatalytic degradation of bisphenol A reaches 76.2% with 5 wt% Ag-doped BiVO ₄ within 180 min irradiation time. Similarly, the Ag-loaded BiVO ₄ could completely inactivate E. coli cells within 30 min under visible light irradiation. The disruption of the cell membrane as well as degradation of protein and DNA exhibited constituted evidence for antibacterial activity towards E. coli . Moreover, the bactericidal mechanisms involved in the photocatalytic disinfection process were systematically investigated.

Microorganisms produce a range of chemical substances representing a vast diversity of fascinating molecular architectures not available in any other system. Among them,Streptomycesare frequently used to produce useful enzymes and a wide variety of secondary metabolites with potential biological activities.Streptomycesare preferred over other microorganisms for producing more than half of the clinically useful naturally originating pharmaceuticals. However, these compounds are usually produced in very low amounts (or not at all) under typical laboratory conditions. Despite the superiority ofStreptomyces, they still lack well documented genetic information and a large number of in-depth molecular biological tools for strain improvement. Previous attempts to produce high yielding strains required selection of the genetic material through classical mutagenesis for commercial production of secondary metabolites, optimizing culture conditions, and random selection. However, a profound effect on the strategy for strain development has occurred with the recent advancement of whole-genome sequencing, systems biology, and genetic engineering. In this review, we demonstrate a few of the major issues related to the potential of “-omics” technology (genomics, transcriptomics, proteomics, and metabolomics) for improving streptomycetes as an intelligent chemical factory for enhancing the production of useful bioactive compounds.