Microbial functional genes elucidate environmental drivers of biofilm metabolism in glacier-fed streams

Ze Ren,James J Elser,Qiudong Zhao,Hongkai Gao

doi:10.1038/s41598-017-13086-9

Abstract

Benthic biofilms in glacier-fed streams harbor diverse microorganisms driving biogeochemical cycles and, consequently, influencing ecosystem-level processes. Benthic biofilms are vulnerable to glacial retreat induced by climate change. To investigate microbial functions of benthic biofilms in glacier-fed streams, we predicted metagenomes from 16s rRNA gene sequence data using PICRUSt and identified functional genes associated with nitrogen and sulfur metabolisms based on KEGG database and explored the relationships between metabolic pathways and abiotic factors in glacier-fed streams in the Tianshan Mountains in Central Asia. Results showed that the distribution of functional genes was mainly associated with glacier area proportion, glacier source proportion, total nitrogen, dissolved organic carbon, and pH. For nitrogen metabolism, the relative abundance of functional genes associated with dissimilatory pathways was higher than those for assimilatory pathways. The relative abundance of functional genes associated with assimilatory sulfate reduction was higher than those involved with the sulfur oxidation system and dissimilatory sulfate reduction. Hydrological factors had more significant correlations with nitrogen metabolism than physicochemical factors and anammox was the most sensitive nitrogen cycling pathway responding to variation of the abiotic environment in these glacial-fed streams. In contrast, sulfur metabolism pathways were not sensitive to variations of abiotic factors in these systems.

Highlights

Glaciers provide vital water resources[1,2,3] and harbor complex microbial communities[4,5,6], in arid regions in Central Asia[7,8,9,10]
We predicted metagenomes from 16s rRNA gene sequence data using PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States)[46], identified functional genes associated with nitrogen and sulfur metabolisms based on KEGG (Kyoto Encyclopedia of Genes and Genomes) database[47], and explored the relationships between metabolic pathways and abiotic factors
Mantel tests were run to assess how functional dissimilarity (Bray-Curtis distance calculated from functional gene abundances) correlated with taxonomic dissimilarity (Bray-Curtis distance calculated from taxon abundances), environmental distance (Euclidean distance), and geographic distance

Summary

Introduction

Glaciers provide vital water resources[1,2,3] and harbor complex microbial communities[4,5,6], in arid regions in Central Asia[7,8,9,10]. Hydrological alteration associated with glacial retreat has the potential to re-structure the habitat template of glacier-fed streams with consequences for the associated biota, including benthic microbial communities and their ecosystem functions. The microbial diversity of benthic biofilms increases with distance from the source glacier, and declines with glacier area proportion, glacier source proportion, and elevation[14,24] This diversity decreases with glacial retreat, illustrating the sensitivity of benthic microbial communities to the effects of climate change[14]. Metagenomics reflects potential rather than realized functional capacity, our data offer a window into the poorly known metabolism of benthic biofilms in glacier-fed streams, providing insights into the potential impacts of glacial melting on the ecosystem function

Methods

Results

Conclusion