Abstract
Actinobacteria are a group of ecologically important bacteria capable of producing diverse bioactive compounds. However, much remains unknown about the taxonomic and metabolic diversities of actinobacteria from many geographic regions and ecological niches. In this study, we report the isolation of actinobacteria from moss and moss-associated rhizosphere soils in Thailand. Among the 89 isolates analyzed for their bioactivities, 86 strains produced indole-3-acetic acid (IAA, ranging from 0.04 to 59.12 mg/L); 42 strains produced hydroxamate type of siderophore; 35 strains produced catecholate type of siderophore; 21 strains solubilized tricalcium phosphate; and many strains exhibited antagonistic activities against one to several of the seven selected plant, animal, and human pathogens. Overall, actinobacteria from the rhizosphere soil of mosses showed greater abilities to produce IAA and siderophores and to solubilize tricalcium phosphate than those from mosses. Among these 89 isolates, 37 were analyzed for their 16S rRNA gene sequences, which revealed their diverse phylogenetic distributions among seven genera, Streptomyces, Micromonospora, Nocardia, Actinoplanes, Saccharothrix, Streptosporangium, and Cryptosporangium. Furthermore, gas chromatography-mass spectrometry analyses of ethyl acetate crude extracts of three selected isolates with inhibitory effects against a methicillin-resistant Staphylococcus aureus strain revealed diverse metabolites with known antimicrobial activities. Together, our results demonstrate that actinobacteria from mosses in Thailand are taxonomically diverse and capable of producing a range of metabolites with plant-growth-promoting and microbial pathogen-inhibiting potentials.
Highlights
We discovered that actinobacteria belonging to three genera Nocardia, Streptomyces, and Saccharothrix were capable of solubilizing phosphate on PVK agar
Metagenomics-based studies of endophytic actinobacteria revealed that Streptomyces sp. was the most abundant genus [1,3], similar to what we found in this study
The species of moss, culture medium, and pre-treatment condition all influenced the isolation of actinobacteria from mosses and from moss-associated rhizospheric soil
Summary
Actinobacteria are common components of endophytic microbiota of medicinal plants [2,3] and have been found in the rhizosphere of numerous plants, including crops, such as wheat [4], yam [5], and pea [6]. These plant-associated actinobacteria can employ several mechanisms to influence plant growth, such as enhancing nitrogen fixation, phosphate solubilization, iron acquisition through secreting siderophores, and production of phytohormones [7]. Such a result suggests a potentially important role of actinobacteria in mosses
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