**Abstract**

"Actinobacteria" are of significant economic value to mankind since agriculture and forestry depend on their soil system contribution. The organic stuff of deceased creatures is broken down into soil, and plants are able to take the molecule up again. Actinobacteria can be used for sustainable agriculture as biofertilizers for the improvement of plant growth or soil health by promoting different plant growth attributes, such as phosphorus and potassium solubilization, production of ironchelating compounds, phytohormones, and biological nitrogen attachment even under the circumstances of natural and abiotic stress. Nanotechnology has received considerable interest in recent years due to its predicted impacts on several key fields such as health, energy, electronics, and the space industries. Actinobacterial biosynthesis of nanoparticles is a dependable, environmentally benign, and significant element toward green chemistry, which links together microbial biotechnology and nanobiology. Actinobacterial-produced antibiotics are common in nearly all of the medical treatments, and they are also recognized to aid in the biosynthesis of excellent surface and size properties of nanoparticles. Bioremediation using microorganisms is relatively safe and more efficient. Actinobacteria use carbon toxins to synthesize economically viable antibiotics, enzymes, and proteins as well. These bacteria are the leading microbial phyla that are beneficial for deterioration and transformation of organic and metal substrates.

**Keywords:** Actinobacteria, *Streptomyces*, PGPR, agriculture, nanoparticles, bioremediation

### **1. Introduction**

One of the largest taxonomic groups of bacteria, Actinobacteria, are generally gram-positive with high Guanine + Cytosine (G + C) content (usually around 70%), a common marker in bacterial systematics [1, 2]. They are unicellular, filamentous, spore-forming, motile, or nonmotile and can be aerobic or anaerobic in nature [3]. The morphological structure ranges from coccoid (*Micrococcus*) and rod-coccoid (*Arthrobacter*) to fragmenting hyphal forms

(*Nocardia*) and branched mycelium (*Streptomyces*) [4]. In culture media, actinobacterial colonies have a powdery consistency and adhere tightly to the agar surface, forming hyphae and conidia/sporangia-like fungi on (aerial mycelium) or under (substrate mycelium) the agar surface [2, 5]. Found in a plethora of environment, including terrestrial and aquatic (both marine and freshwater), they share features of both the bacteria (chromosomes organized in a nucleoid and cell wall made of peptidoglycan) as well as fungi (presence of mycelium) [1, 2, 6]. Actinobacteria possess high ecological significance with an immense ability to produce organic acids, fix nitrogen from the atmosphere, and impart an essential role in the decomposition of organic compounds including cellulose and chitin, thus contributing to organic matter turnover and the carbon cycle. This further renews the supply of nutrients in the soil and forms humus [2, 3]. They play a crucial role not only in agriculture but also in the clinical and pharmaceutical industry [7]. Antibiotics, antifungals, enzymes, enzyme inhibitors, antivirals, antioxidants, anticholesterol, antiprotozoal, anticancer, and immunosuppressant are few of the beneficial secondary metabolites with therapeutic implications produced by Actinobacteria [1, 6, 7]. Some of the important genera of Actinobacteria found in soil are *Actinoplanes*, *Micromonospora*, *Nocardia*, *Streptomyces*, and *Streptosporangium* [2], and found as plant or animal pathogens are *Corynebacterium*, *Mycobacterium*, or *Nocardi*a [1].
