Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
Division of Earth and Ecosystem Science, Desert Research Institute, Reno, Nevada, USA.
Appl Environ Microbiol. 2018 Mar 19;84(7). doi: 10.1128/AEM.02322-17. Print 2018 Apr 1.
Snow algae can form large-scale blooms across the snowpack surface and near-surface environments. These pigmented blooms can decrease snow albedo and increase local melt rates, and they may impact the global heat budget and water cycle. Yet, the underlying causes for the geospatial occurrence of these blooms remain unconstrained. One possible factor contributing to snow algal 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 -bacterial coculture through laboratory-based experimentation. Fo was capable of stimulating snow algal growth and increased the algal growth rate in otherwise Fe-depleted cocultures. Fo-bearing systems also exhibited a decrease in the ratio of bacteria to algae compared to those of Fe-depleted conditions, suggesting a shift in microbial community structure. The coculture also increased the rate of Fo dissolution relative to that of an abiotic control. Analysis of 16S rRNA genes in the coculture 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%) operational taxonomic units (OTUs). These data provide unequivocal evidence that mineral dust can support elevated snow algal growth under otherwise Fe-depleted growth conditions and that snow algal microbial communities can enhance mineral dissolution under these conditions. Fe, a key micronutrient for photosynthetic growth, is necessary to support the formation of high-density snow algal blooms. The laboratory experiments described herein allow for a systematic investigation of the interactions of snow algae, bacteria, and minerals 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 algal-bacterial coculture. This evidence includes (i) an observed increase in snow algal density and growth rate, (ii) decreased ratios of bacteria to algae in Fo-containing cultures relative to those of cultures grown under similarly Fe-depleted conditions with no mineral-bound Fe present, and (iii) increased Fo dissolution rates in the presence of algal-bacterial cocultures relative to those of 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 algal blooms capable of lowering snow albedo and increasing snow melt rates on regional, and possibly global, scales.
雪藻可以在积雪表面和近表面环境中形成大规模的水华。这些色素水华可以降低雪的反照率并增加局部融化率，从而可能影响全球热量平衡和水循环。然而，这些水华发生的地理空间原因仍然受到限制。造成雪藻水华的一个可能因素是矿物灰尘作为微量元素源的存在。我们通过实验室实验研究了含铁（Fe）矿物，包括镁铁橄榄石（Fo，MgFeSiO）、针铁矿、蒙脱石和黄铁矿作为细菌 - 细菌共培养物的 Fe 源的生物利用度。Fo 能够刺激雪藻生长，并在其他缺铁共培养物中增加藻类生长速度。与缺铁条件相比，含有 Fo 的系统还表现出细菌与藻类的比例降低，这表明微生物群落结构发生了变化。与非生物对照相比，共培养物还增加了 Fo 的溶解速率。共培养物中 16S rRNA 基因的分析确定了 、 、 和 ，这些菌均常见于雪和冰环境中。未检测到古菌。 和 ，已知它们可以提高矿物风化速率，构成了前 8 个（>1%）操作分类单元（OTUs）中的两个。这些数据提供了确凿的证据，证明矿物灰尘可以在其他缺铁生长条件下支持雪藻的高生长，并证明在这些条件下雪藻微生物群落可以增强矿物溶解。Fe 是光合作用生长的关键微量元素，是形成高密度雪藻水华所必需的。本文所述的实验室实验允许系统地研究雪藻、细菌和矿物质的相互作用及其在动员和吸收矿物质结合的 Fe 方面的能力。结果提供了确凿而全面的证据，证明含铁 Fo 中的矿物质结合的 Fe 对 雪藻在藻 - 细菌共培养物中是生物可利用的。这一证据包括：（i）观察到雪藻密度和生长速率增加；（ii）在含有 Fo 的培养物中细菌与藻类的比例相对于在没有矿物质结合的 Fe 存在且同样缺铁的条件下生长的培养物中降低；（iii）在存在藻 - 细菌共培养物的情况下 Fo 的溶解速率相对于无生命矿物质对照物增加。这些结果对矿物灰尘在为雪微生物组提供微量元素方面的作用具有重要意义，这可能有助于支持在区域乃至全球范围内降低雪反照率并增加雪融化率的密集雪藻水华的形成。
