MICROBIAL COMMUNITY IN HYPERALKALINE STEEL SLAG-FILL EMULATES SERPENTINIZING SPRINGS

To date, a majority of studies of microbial life in hyperalkaline settings focus on environments that are also highly saline (haloalkaline). Haloalkaline conditions offer microbes abundant workarounds to maintain pH homeostasis, as salt ions can be exchanged for protons by dedicated antiporter proteins. Yet hyperalkaline freshwater systems also occur both naturally and anthropogenically, such as the slag fill aquifers around former Lake Calumet, Chicago, IL, USA. Weathering of these waste minerals leaches highly alkaline Ca(OH)₂ into the area’s groundwater, driving pH up to 13, and causing massive CaCO₃ precipitation on contact with atmospheric CO₂.

In this study, 16S rRNA gene sequences and metagenomic sequence libraries were collected to assess the taxonomic composition and functional potential of microbes present in these slag-polluted waterways. Relative 16S rRNA gene abundances in Calumet sediment and water samples describe community compositions not significantly divergent from those in nearby circumneutral conditions. Major differences in composition are mainly driven by Proteobacteria, primarily one sequence cluster closely related to Hydrogenophaga, which comprises up to 85% of 16S rRNA gene abundance in hyperalkaline surface sediments.

Sequence identity indicates the highly abundant species belongs to the recently established genus Serpentinomonas, a bacterial lineage associated with natural freshwater hyperalkaline serpentinizing springs. Genomic features of Serpentinomonas bacteria indicate they are uniquely adapted to utilizing products of serpentinization, specifically carbonates and hydrogen gas.