A total of 118 actinobacterial isolates were collected from the three types of termite nests (mound, carton, and subterranean nests) to evaluate their potential as a source of bioactive actinobacteria with antimicrobial activity. The highest number (67 isolates) and generic abundance (7 known genera) of actinobacterial isolates were obtained from carton nests. Streptomyces was the dominant genus in each type of termite nest. In the non-Streptomyces group, Nocardia was the dominant genus detected in mound and carton nests, while Pseudonocardia was the dominant genus in subterranean nests. A discovery trend of novel species (<99% similarity in the 16S rRNA gene sequence) was also observed in the termite nests examined. Each type of termite nest housed >20% of bioactive actinobacteria that could inhibit the growth of at least one test organism, while 12 isolates, belonging to the genera Streptomyces, Amycolatopsis, Pseudonocardia, Micromonospora and Nocardia, exhibited distinct antimicrobial activities. Streptomyces sp. CMU-NKS-3 was the most distinct bioactive isolate. It was closely related to S. padanus MITKK-103T, which was confirmed by 99% similarities in their 16S rRNA gene sequences. The highest level of extracellular antimicrobial substances was produced by the isolate CMU-NKS-3, which was grown in potato dextrose broth and exhibited a wide range (6.10×10−4–1.25 mg mL−1) of minimum inhibitory concentrations against diverse pathogens. We concluded that termite nests are an abundant source of bioactive strains of cultivable actinobacteria for future biotechnological needs.

A novel Gram-stain-positive bacterium designated CMU-NKS-70T was isolated from a subterranean termite nest and characterized using a polyphasic approach. The strain exhibited branching, pinkish-cream aerial mycelium and cream-brown substrate mycelium, and formed chains of rod-like spores. The 16S rRNA gene sequence analyses indicated that strain CMU-NKS-70T belonged to the genus Pseudonocardia, showing high similarity with Pseudonocardia oroxyli D10T (98.9 % 16S rRNA gene sequence similarity), Pseudonocardia xishanensis YIM 63638T (98.9 %) and Pseudonocardia kujensis A4038T (98.5 %). However, DNA-DNA relatedness values between strains CMU-NKS-70T and the closest phylogenetically related species ranged from 40.5±2.9 to 48.6±0.7 %. Whole-cell hydrolysates of strain CMU-NKS-70T consisted of meso-diaminopimelic acid, glucose, galactose, arabinose, mannose, ribose and rhamnose. The predominant menaquinone was MK-8(H4). The major cellular fatty acids (>10 %) were iso-C16 : 0, C16 : 0, C16 : 1ω7c and/or iso-C15 : 0 2-OH and 10-methyl C16 : 0. The polar lipids detected were phosphatidylethanolamine, phosphatidylmethylethanolamine, hydroxyphosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, three unidentified glycolipids and two unidentified phospholipids. The G+C content of genomic DNA was 71.9 mol%. The physiological and biochemical properties also supported the phenotypic distinction of strain CMU-NKS-70T from its closely related species. On the basis of evidence from this study using a polyphasic approach, strain CMU-NKS-70T represents a novel species of the genus Pseudonocardia for which the name Pseudonocardia thailandensis sp. nov. is proposed. The type strain is CMU-NKS-70T (=JCM 31292T=TBRC 2000T).