The demand for natural colors is increasing day by day due to harmful effects of some synthetic dyes. Bacterial and fungal pigments provide a readily available alternative source of naturally derived pigments. In contrast to other natural pigments, they have enormous advantages including rapid growth, easy processing, and independence of weather conditions. Apart from colorant, bacterial and fungal pigments possess many biological properties such as antioxidant, antimicrobial and anticancer activity. This review outlines different types of pigments. It lists some bacterial and fungal pigments and current bacterial and fungal pigment status and challenges. It also focuses on possible fungal and bacterial pigment applications.

Abiotic stressors, such as drought, flooding, extreme temperature, soil salinity, and metal toxicity, are the most important factors limiting crop productivity. Plants use their innate biological systems to overcome these abiotic stresses caused by environmental and edaphic conditions. Microorganisms that live in and around plant systems have incredible metabolic abilities in mitigating abiotic stress. Recent advances in multi-omics methods, such as metagenomics, genomics, transcriptomics, and proteomics, have helped to understand how plants interact with microbes and their environment. These methods aid in the construction of various metabolic models of microbes and plants, resulting in a better knowledge of all metabolic exchanges engaged during interactions. Actinobacteria are ubiquitous and are excellent candidates for plant growth promotion because of their prevalence in soil, the rhizosphere, their capacity to colonize plant roots and surfaces, and their ability to produce various secondary metabolites. Mechanisms by which actinobacteria overcome abiotic stress include the production of osmolytes, plant hormones, and enzymes, maintaining osmotic balance, and enhancing nutrient availability. With these characteristics, actinobacteria members are the most promising candidates as microbial inoculants. This review focuses on actinobacterial diversity in various plant regions as well as the impact of abiotic stress on plant-associated actinobacterial diversity and actinobacteria-mediated stress mitigation processes. The study discusses the role of multi-omics techniques in expanding plant–actinobacteria interactions, which aid plants in overcoming abiotic stresses and aims to encourage further investigations into what may be considered a relatively unexplored area of research.

Dracaena cochinchinensis Lour. is an ethnomedicinally important plant used in traditional Chinese medicine known as dragon’s blood. Excessive utilization of the plant for extraction of dragon’s blood had resulted in the destruction of the important niche. During a study to provide a sustainable way of utilizing the resources, the endophytic Actinobacteria associated with the plant were explored for potential utilization of their medicinal properties. Three hundred and four endophytic Actinobacteria belonging to the genera Streptomyces, Nocardiopsis, Brevibacterium, Microbacterium, Tsukamurella, Arthrobacter, Brachybacterium, Nocardia, Rhodococcus, Kocuria, Nocardioides, and Pseudonocardia were isolated from different tissues of D. cochinchinensis Lour. Of these, 17 strains having antimicrobial and anthracyclines-producing activities were further selected for screening of antifungal and cytotoxic activities against two human cancer cell lines, MCF-7 and Hep G2. Ten of these selected endophytic Actinobacteria showed antifungal activities against at least one of the fungal pathogens, of which three strains exhibited cytotoxic activities with IC₅₀-values ranging between 3 and 33 μg·mL⁻¹. Frequencies for the presence of biosynthetic genes, polyketide synthase- (PKS-) I, PKS-II, and nonribosomal peptide synthetase (NRPS) among these 17 selected bioactive Actinobacteria were 29.4%, 70.6%, and 23.5%, respectively. The results indicated that the medicinal plant D. cochinchinensis Lour. is a good niche of biologically important metabolites-producing Actinobacteria.

Diseases caused by Staphylococcus warneri have a significant impact on human health. We evaluated the antibacterial activity of silver nanoparticles (synthesized using the endophytic strain SYSU 333150) against Staphylococcus warneri. The strain SYSU 333150 was isolated from the roots of Borszczowia aralocaspica Bunge. The 16S rRNA sequence results suggest that SYSU 333150 belongs to the genus Isoptericola and is likely a new species. Photo-irradiation was used to synthesize silver nanoparticles, which were characterized using UV-visible spectroscopy, transmission electron microscopy and X-ray diffraction. The nanoparticles were spherical and measured to be11 to 40 nm. X-ray diffraction revealed four peaks corresponding to the 111, 200, 220 and 311 planes of the face-centered cubic lattice, indicating a crystalline nature. Fourier transform infrared spectroscopy suggested that the metabolites in the culture supernatant were likely reducing and capping agents. The silver nanoparticles possessed antimicrobial activity (14 mm zone of inhibition) against Staphylococcus warneri, which was likely a result of DNA cleavage. The synthesized silver nanoparticles have potent antibacterial activity against Staphylococcus warneri and can be used to control infection.