ABSTRACT
Actinobacteria remain to be one of the major sources for new antibiotics, which historically play an essential role in human's fight against infectious diseases. Due to the emergence of resistant pathogenic microorganisms such as bacteria, fungi and viruses, it is imperative to develop new and effective drugs against these pathogens. The symbiotic actinobacteria residing inside the animals are becoming more and more important as a new source for drug discovery, as well as a "hotspot" in the field of microbial medicine. During the long period of evolution, a specific host-microbe mutualism is formed between the symbiotic bacteria and their hosts of animals. In this unique ecosystem, the secondary metabolites produced by bacteria are well tolerated by the hosts, meanwhile, are able to selectively suppress pathogenic microorganisms, thus providing a specific protection to their hosts. These secondary metabolites encompass a large variety of structural diversities of natural products, and so far, the reported biological activities are including antibacterial, antifungal, antiviral, antitumor, and immunomodulatory effects, which give them a great potential in the field of drug discovery. Herein, we review the secondary metabolites of animal symbiotic actinobacteria and their biological activities within the recent decade, by which to provide a viewpoint for future research of drug discovery from actinobacteria.