Diversity and Co-Occurrence Patterns of Fungal and Bacterial Communities from Alkaline Sediments and Water of Julong High-Altitude Hot Springs at Tianchi Volcano, Northeast China

SIMPLE SUMMARY: Volcanic hot springs are considered of particular interest in biology as precious sources of peculiar microorganisms adapted to extreme environmental conditions. The Julong high-altitude volcanic hot springs in northeast China are characterized by alkali, sulfur and metal enrichment. The microbial communities colonizing these intriguing habitats still remain completely unknown. We carried out the present study in order to shed light on the Julong hot springs fungal and bacterial community diversity, structure and interactions, and to understand the impact of pH on the microorganisms colonizing the investigated environment. We detected a large variety of typical photosynthetic, thermophilic, alkalophilic, antimicrobial-active, and sulfide- and metal-oxidizing microbial taxa representing clear links to the extreme properties of the studied environment. Results showed a striking microorganism community variation strongly influenced by pH under clearly alkaline conditions. Our analyses suggests that mutualistic relationships might be common among microorganisms coexisting in the Julong hot springs, especially for the bacterial community. This study provides new insights in the diversity and ecological interactions of microorganisms living in high-altitude volcanic hot springs and contributes to our knowledge of abiotic factors influencing the microbial community in the analyzed extreme environment. ABSTRACT: The Julong high-altitude volcanic hot springs in northeast China are of undeniable interest for microbiological studies due to their unique, extreme environmental conditions. The objective of this study was to provide a comprehensive analysis of the unexplored fungal and bacterial community composition, structure and networks in sediments and water from the Julong hot springs using a combination of culture-based methods and metabarcoding. A total of 65 fungal and 21 bacterial strains were isolated. Fungal genera Trichoderma and Cladosporium were dominant in sediments, while the most abundant fungi in hot spring water were Aspergillus and Alternaria. Bacterial communities in sediments and water were dominated by the genera Chryseobacterium and Pseudomonas, respectively. Metabarcoding analysis revealed significant differences in the microorganism communities from the two hot springs. Results suggested a strong influence of pH on the analyzed microbial diversity, at least when the environmental conditions became clearly alkaline. Our analyses indicated that mutualistic interactions may play an essential role in shaping stable microbial networks in the studied hot springs. The much more complicated bacterial than fungal networks described in our study may suggest that the more flexible trophic strategies of bacteria are beneficial for their survival and fitness under extreme conditions.