Actinobacteria, which share the characteristics of both bacteria and fungi, are widely distributed in both terrestrial and aquatic ecosystems, mainly in soil, where they play an essential role in recycling refractory biomaterials by decomposing complex mixtures of polymers in dead plants and animals and fungal materials. They are considered as the biotechnologically valuable bacteria that are exploited for its secondary metabolite production. Approximately, 10,000 bioactive metabolites are produced by Actinobacteria, which is 45% of all bioactive microbial metabolites discovered. Especially Streptomyces species produce industrially important microorganisms as they are a rich source of several useful bioactive natural products with potential applications. Though it has various applications, some Actinobacteria have its own negative effect against plants, animals, and humans. On this context, this chapter summarizes the general characteristics of Actinobacteria, its habitat, systematic classification, various biotechnological applications, and negative impact on plants and animals.

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A novel trinuclear zinc(II) complex [Zn3L2(μ‐O2CCH3)2(CH3OH)4] (1) that contains an N,O‐donor Schiff base ligand {H2L = 2‐[(2‐hydroxyphenylimino)methyl]‐6‐methoxyphenol} has been synthesized and crystallographically characterized. The X‐ray crystal structure of 1 contains three zinc(II) centers, which have distorted‐octahedral coordination geometry, and the molecule crystallizes in the Pbcn space group. The zinc(II) complex displays significant catecholase oxidation activity in methanolic medium through a ligand‐centered radical pathway. This is the first example of catecholase oxidation through a trinuclear zinc(II)–Schiff base complex by means of the formation of a mononuclear intermediate as [ZnL(dtbc)] (dtbc = 3,5‐di‐tert‐butylcatechol). The fluorescence property of 1 indicates that it can serve as a potential photoactive material. It effectively cleaves the double strand of pBR 322 plasmid DNA at a given concentration (25 μM). The complex shows remarkable cytotoxicity against a human hepatocarcinoma cell line (HepG2).

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A mononuclear cobalt(III) complex [Co(bpy) 2 Cl 2 ]NO 3 •2H 2 O (1) (bpy = 2,2-bipyridine) has been synthesized and crystallographically characterized. Self-assembly of the lattice water molecules from rectangular tetrameric water cluster interacts with nitrate anion along the c-axis forming a six membered hexagonal water-nitrate cluster. It presents a new mode of association of water molecules with nitrate molecules which is not predicted theoretically or found experimentally. The molecule effectively cleaves bacterial genomic DNA and shows important cytotoxicity against human hepatocarcinoma cell (HepG2).