Bioavailability of Mineral-Bound Iron to a Snow Algal-Bacterial Coculture and Implications for Albedo-Altering Snow Algal Blooms

Abstract

Snow algae can form large-scale blooms across the snowpack surface and near-surface environments. These pigmented blooms can decrease snow albedo, increase local melt rates, and may impact the global heat budget and water cycle. Yet, underlying causes for the geospatial occurrence of these blooms remain unconstrained. One possible factor contributing to snow algae blooms is the presence of mineral dust as a micronutrient source. We investigated the bioavailability of iron (Fe) -bearing minerals, including forsterite (Fo, MgFeSiO), goethite, smectite and pyrite as Fe sources for a - bacteria co-culture through laboratory-based experimentation. Fo was capable of stimulating snow algal growth and increased the algal growth rate in otherwise Fe-depleted co-cultures. Fo-bearing systems also exhibited a decrease in bacteria:algae ratios compared to Fe-depleted conditions, suggesting a shift in microbial community structure. The co-culture also increased the rate of Fo dissolution relative to an abiotic control. Analysis of 16S rRNA genes in the co-culture identified , and , all of which are commonly found in snow and ice environments. Archaea were not detected. and , which are known to enhance mineral weathering rates, comprised two of the top eight (> 1 %) OTUs. These data provide unequivocal evidence that mineral dust can support elevated snow algae growth under otherwise Fe-depleted growth conditions, and that snow algae can enhance mineral dissolution under these conditions. Fe, a key micronutrient for photosynthetic growth, is necessary to support the formation of high-density snow algae blooms. The laboratory experiments described herein allow for a systematic investigation of snow algae-bacteria-mineral interactions and their ability to mobilize and uptake mineral-bound Fe. Results provide unequivocal and comprehensive evidence that mineral-bound Fe in Fe-bearing Fo was bioavailable to snow algae within an algae-bacteria co-culture. This evidence includes: 1) an observed increase snow algae density and growth rate; 2) decreased bacteria:algae ratios in Fo-containing cultures relative to cultures grown under similarly Fe-depleted conditions with no mineral-bound Fe present; and 3) increased Fo dissolution rates in the presence of algae-bacteria co-cultures relative to abiotic mineral controls. These results have important implications for the role of mineral dust in supplying micronutrients to the snow microbiome, which may help support dense snow algae blooms capable of lowering snow albedo, and increase snow melt rates on regional, and possibly global, scales.

Snow and Glacial Algae: A Review1

“…Fe, a key micronutrient for photosynthetic growth, is necessary to support the formation of high‐density snow algal blooms (Harrold et al. ). Using Fe 90 in Chloromonas brevispina ‐bacterial coculture experiments, snow algal growth was stimulated.…”

Alpine Snow Algae Microbiome Diversity in the Coast Range of British Columbia

“…isolated from snow grew better in the presence of bacteria from a field sample than when plated with an antibiotic. Another study, co-culturing snow bacteria and Chloromonas brevispina, showed increased iron containing mineral dissolution, which stimulated algae growth, suggesting bacteria could help snow algae obtain bioavailable iron from mineral dust (Harrold et al, 2018). Although little data exist for algae-fungal mutualisms outside of lichens, metabolite exchange can occur between yeast (Saccharomyces cerevisiae) and microalgae (Chlamydomonas reinhardtii; Hom and Murray, 2014).…”

Biological albedo reduction on ice sheets, glaciers, and snowfields

“…Therefore, bacteria and fungi may increase ecosystem carrying capacity, and thus the abundance of algae and algal BAR, through the liberation of phosphorus (P) and Fe (and other micronutrients) from rock flour and surface debris, while producing labile organic C that is readily consumed by heterotrophs through photosynthesis (Kellerman et al, 2020;Musilova et al, 2016). Experimental evidence supports this thesis; bacteria enhance the growth rate and abundance of snow algae in the presence of Fe-bearing minerals (Harrold et al, 2018;Lutz et al, 2015;Phillips-Lander et al, 2020). Viruses have not been directly linked to BAR but they may play an indirect role by regulating bacterial mortality, thereby influencing levels of dissolved organic matter (Anesio et al, 2007;Bellas et al, 2013).…”

“…Snow and ice algae are water-limited and potentially nutrient-limited (Anesio et al, 2017;Ganey et al, 2017;Havig, 2017, 2020;Lutz et al, 2015;Takeuchi et al, 2006). Algae and other psychrophilic microorganisms are also known to interact in their use of several limiting resources [e.g., C, iron (Fe), and N (Anesio et al, 2017;Harrold et al, 2018;Havig and Hamilton, 2019;Hodson et al, 2008;Phillips-Lander et al, 2020;Stibal et al, 2009;Telling et al, , 2011]. Therefore, bacteria and fungi may increase ecosystem carrying capacity, and thus the abundance of algae and algal BAR, through the liberation of phosphorus (P) and Fe (and other micronutrients) from rock flour and surface debris, while producing labile organic C that is readily consumed by heterotrophs through photosynthesis (Kellerman et al, 2020;Musilova et al, 2016).…”