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

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.

Ecological Stoichiometry of the Mountain Cryosphere

“…Glacier-fed streams and lakes reflect the integration of both upstream and in situ processes (Figure 1; Brittain and Milner, 2001;Mindl et al, 2007;Robinson et al, 2016;Hotaling et al, 2017b;Ren and Gao, 2019). Melting glaciers supply key water, sediment, and nutrients to aquatic ecosystems, determining their optical properties, resource availability, and the structure and composition of biological communities (Laspoumaderes et al, 2013;Martyniuk et al, 2014;Rose et al, 2014;Hotaling et al, 2017b;Ren et al, 2017a ; Figures 4, 5). In general, glacier-fed streams and lakes are characterized by considerable sediment input from upstream grinding of bedrock, cold temperatures (e.g., < 10 • even in summer), and dynamic water levels.…”

Microbial assemblages reflect environmental heterogeneity in alpine streams

“…As high-elevation headwaters, alpine streams are a key hydrological link between cryospheric processes and downstream habitats, both freshwater and marine (Hood, Battin, Fellman, O'Neel, & Spencer, 2015;Hotaling, Hood, et al, 2017;O'Neel et al, 2015). To date, most studies of microbial ecology in alpine headwaters have emphasized ice-fed streams, and particularly those fed by surface glaciers (Freimann et al, 2013a;Ren, Gao, Elser, & Zhao, 2017;Wilhelm et al, 2013) with rare rock glacier examples (Fegel et al, 2016). However, there has been considerably less focus on other stream types (but see Esposito et al, 2016), and no comparisons across multiple stream types in the same geographic region have been made.…”

Microbial community structure and functional properties in permanently and seasonally flooded areas in Poyang Lake

“…In our study, high proportions of positive correlations between nodes in the two networks suggested the interdependencies among bacterial taxa under environmental disturbance. Topological parameters provide important information to help us to understand microbial community structure 2,3,47,52 . Higher values of network centralization and heterogeneity in the emerged areas than in the inundated areas suggested that there were many tightly connected bacterial modules (subnetworks in the whole network) in the emerged areas.…”

“…S2c). In general, ANR processes are much more prevalent than DNR processes in natural ecosystems 3,71 , and high concentrations of NH 4 + could stimulate assimilatory pathways 67,71,72 . The reduction processes of NO 3 − to NO 2 − and then to NH 4 + are part of the ANR processes, which usually occur in anaerobic environments such as sediment and soil 73 .…”

“…The reduction processes of NO 3 − to NO 2 − and then to NH 4 + are part of the ANR processes, which usually occur in anaerobic environments such as sediment and soil 73 . In the wet season, a large amount of mineralized nitrogen (especially NH 4 + ) could be easily dissolved in pore water and be rapidly released into lake water, and these mineralized nitrogen types could be used by bacterial communities as an energy source 3,71,74 . DNR is another nitrogen catabolic pathway that can retain nitrogen in the system in a bioavailable form for further biological processes 71,75 .…”