The Influence of Glacial Rock Flour (GRF) on Algal Growth and Associated Microbiomes

Global anthropogenic CO₂ emissions are rapidly increasing, posing a threat to the biosphere resulting in cascading consequences for the ecosystems. Glacial Rock Flour (GRF), that is a fine grained silicate material formed by glacial erosion on the Greenlandic bedrock, can promote growth of agricultural crops (maize and potato) and can also stimulate oceanic phytoplankton growth [1, 2]. The aim of our study was to explore the potential of GRF as a novel biofertilizer for the biotechnological relevant microalga Isochrysis galbana, and to assess whether it affected the microbiome composition of the alga.

By replacing a traditional trace metal solution in the algal growth media with GRF (0.25, 0.5, or 1 g/L), we found that GRF could stimulate growth of xenic I. galbana and even outperformed traditional algal media. GRF had direct impact on exponential growth of the algae, resulting in the highest observed cell counts, growth rates and chlorophyll a content. However, the cell counts after 14 days were similar for all culture conditions. Metataxonomic analyses using 16S rRNA gene amplicons revealed that the presence of GRF did not significantly alter the microbiome of I. galbana [3].

The results strongly suggest that GRF has promising potential as a novel biofertilizer for enhancing microalgae growth without disrupting or compromising the native algal microbiome. Future work should investigate how GRF might alter the functional profile of a microalgae, as well as its effect on axenic algal cultures and on microbiomes extracted from algae.