Abstract
Actinomycetes in extreme alpine habitat have attracted much attention due to their unique physiological activities and functions. However, little is known about their ecological distribution and diversity. Here, we explored the phylogenetic relationship and physiological heterogeneity of cultivable actinomycetes from near-root soils of different plant communities in the Laohu Ditch (2200 – 4200 m) and Gaize County area (5018 – 5130 m) on the Qinghai-Tibetan Plateau. A total of 128 actinomycete isolates were obtained, 16S rDNA-sequenced and examined for antimicrobial activities and organic acid, H2S, diffusible pigments, various extracellular enzymes production. Seventy three isolates of the total seventy eight isolates from the Laohu Ditch, frequently isolated from 2200 to 4200 m, were closely related to Streptomyces spp. according to the 16S rDNA sequencing, while four isolates within the genus Nocardia spp. were found at 2200, 2800, and 3800 m. In addition, one potential novel isolate with 92% sequence similarity to its nearest match Micromonospora saelicesensis from the GenBank database, was obtained at 2200 m. From the Gaize County area, fifty Streptomyces isolates varied in diversity at different sites from 5018 to 5130 m. The investigation of phenotypic properties of 128 isolates showed that 94.5, 78.9, 68, 64.8, 53, 51.6, 50, 36.7, 31.2, and 22.7% of the total isolates produced catalase, lipase 2, urease, protease, H2S, lipase 3, amylase, lipase 1, diffusible pigment and organic acid, respectively. The antimicrobial assays of the total isolates revealed that 5, 28, 19, and 2 isolates from Streptomyces spp. exhibited antimicrobial activity against Escherichia coli, Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa, respectively. This study intends to bring helpful insights in the exploitation and utilization of alpine actinomycetes for novel bioactive compounds discovery.
Highlights
Actinomyces had served as the sources of novel antibiotic and bioactive molecule candidates with application in many fields (Ramesh and Mathivanan, 2009; Genilloud et al, 2011)
The study in the high Arctic permafrost of Spitsbergen has shown that there is a high diversity of actinobacterial communities in this alpine soil and many of the phylotypes identified may represent novel, uncultured species, which might be the sources of genetic diversity and novel bioactive compounds (Hansen et al, 2007)
Ivanova et al (2009) presented that a large amount of trehalose and glycerol as cryopreservation additives produced by Streptomyces spp. from the permafrost in Spitsbergen could be a reason for the strains to survive in cold and dry conditions
Summary
Actinomyces had served as the sources of novel antibiotic and bioactive molecule candidates with application in many fields (Ramesh and Mathivanan, 2009; Genilloud et al, 2011). Further studies revealed that production of a range of bioactive metabolites including antibiotics, trehalose, lipase and pigment by actinobacteria from alpine cold habitats, could be a strategy for the strains in response to harsh environmental conditions (Fong et al, 2001; Dillon et al, 2003; Zhang et al, 2008; Babalola et al, 2009; Ivanova et al, 2009; Sivalingam et al, 2019). Malviya et al (2009) documented that some Streptomyces isolates from alpine zones of Pindari glacier region in Indian Himalaya exhibited strong antifungal properties These findings provide evidence that a wide diversity of Actinobacteria can survive in alpine environments, and most of which could yield bioactive compounds. Exploring the phylogenetic and physiological diversity patterns of alpine actinomycetes may provide an opportunity for selecting strains that are under environmental pressures, which may drive adaptions that produce unique biosynthetic or hydrolytic capabilities
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