Diversity of aerobic cold-adapted bacteria and archaea isolated from the Pamir Plateau

Abstract:

[Objective] The Pamir Plateau is characterized by a cold and oligotrophic environment exposed to strong radiation, in which cold-adapted microorganisms are abundant. Using a cultivation-dependent approach, we aimed to reveal the diversity of cold-adapted bacteria and archaea present in the Pamir Plateau. [Methods] Soil samples were collected from a gradient of altitudes in the Pamir Plateau, from which aerobic bacteria and archaea were isolated by different cultivation methods. For the isolation of cold-adapted bacteria, two bacterial culture media were used and the incubation was only conducted at 4℃. For cultivation of archaeal ones, two archaeal culture media were employed, and cultivation was at two temperatures, i.e., 4℃ and 15℃. Sampling was conducted at four altitudes:1 000-2 000 m, 2 000-3 000 m, 3 000-4 000 m and 4 000-5 000 m. All microbial isolates were classified based on their 16S rRNA gene sequences. [Results] A total of 419 strains of aerobic prokaryotes were isolated from the soil samples, which belonged to 118 different species, including 115 bacterial species and 3 archaeal species. These microorganisms fell into 49 genera, 28 families, 18 orders, 8 classes, 5 phyla, and 2 domains. Gammaproteobacteria was the predominant order of cold-adapted bacteria and Actinomycetes constituted the most diverse one. Gammaproteobacteria dominated at altitude of 1 000-4 000 m and Actinobacteria prevailed at altitude of 4 000-5 000 m (the highest altitude). The archaeal isolates belonged to haloarchaea of Natrinema and Haloterrigena, and they were obtained from the samples at altitude of 1 000-2 000 m and at the cultivation temperature of 15℃. Furthermore, among the four culture media used in this work, Gammaproteobacteria isolates were mainly obtained with the two bacterial media whereas the haloarchaea only grew on the archaeal media. Additionally, 23 strains represented new taxa among all isolates, and they belonged to Actinobacteria, Proteobacteria, Bacteroidetes, Firmicutes and Euryarchaeota.[Conclusion] A number of cold-adapted bacteria and three archaeal species were isolated as pure cultures from the Pamir Plateau soil samples. These microorganisms exhibited an altitude-dependent distribution. Furthermore, we found that the isolation experiment was benefitted from utilization of different culture conditions, which was a strategy to be exploited in future work. Together, the present study has yielded the first insights into the composition and diversity of cold-adapted bacteria and archaea in the Pamir Plateau. The obtained microorganisms provide unique resources for exploration of their ecological functions and biotechnological applications.