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Contributors: Paul Reginato1, Pritha Ghosh2, Buz Barstow3, Esteban Gazel4

Lead contact: Paul Reginato ([email protected])

Problem Statement

Motivating Factor

Atmospheric carbon dioxide removal and point-source carbon capture technologies are well-accepted as being necessary for meeting climate goals [1]. Rock weathering in the environment naturally generates alkalinity that draws ~0.3 GtCO2/yr from the atmosphere and converts it to solid carbonates or (bi)carbonates which are transported to the ocean and stably stored [2][3]. Enhanced rock weathering (ERW) technology seeks to accelerate alkalinity generation via mineral dissolution for carbon storage by grinding rocks to increase reactive surface area and exposing them to weathering conditions [4][5]. A core challenge of ERW is cost-effectively increasing mineral dissolution kinetics to enable scaling [6].

Specific Constraint

Microbes can accelerate mineral weathering [7][8][9][10], for example through chelation by siderophores [11], chelation by organic acids [12][13], oxidoreductive chemolithotrophy [14][15], or prevention of surface passivation [16][17]. Biologically-enhanced weathering (bio-ERW) has been proposed, wherein microbes would accelerate weathering in soils or reactors [9][18][19][20], possibly in concert with valuable metal recovery [21][22].

While three studies [23][24][25] have shown microbially-enhanced alkalinity generation, research is constrained by a lack of systematic knowledge of the weathering activity and mechanisms of a broad range of microbes. Some studies have explored bioweathering in specific microbe-mineral pairings (e.g., [16][11][26][27][28] , with one group systematically screening genes in one organism [29][30], but there has been no systematic characterization of microbial weathering and mechanisms. While field-based studies are most application-relevant [9], lab experiments are needed to grow fundamental understanding, since they are more tractable, produce more comparable results, and are more capable of characterizing mechanisms.

Actionable Goals

Microbial catalysis of mineral dissolution should be systematically characterized via lab studies. Microbes or microbial communities and minerals of interest should be systematically paired. Minerals and microbes of interest for bio-ERW can be sourced from the literature [31][7][32][9][33], from functional studies of weathering in natural environments [9][34], or new samples from promising environments. Genetic screens, transcriptomics, and metabolomics should be performed in microbes with high weathering capabilities to discover genetic factors and mechanisms [30]. Integration of microscopy (e.g. SEM) with Raman spectroscopy may be valuable for measuring mineralogical changes [35].

This work should strive to identify promising strains for bio-ERW as well as identify avenues for further mechanistic studies, for example into surfactants or unknown molecular factors involved in bioweathering that may enhance the effects of chelators [36][11] or act separately from them [30].

Additional information

Open Questions

• What is a starting list of specific microbial species worth screening?

• What is a systematic list of promising natural mineral environments to sample novel microbes, and partners with access to them?

• What are the constraints on bio-ERW implementation, based on techno-economic and life cycle analysis [37]?

• What are the estimated bounds on performance of bio-ERW, based on both lab measurements and theoretical calculations?

Assumptions

• Experimental methods are available to systematically perform weathering measurements.

• Lab-based characterization of microbial weathering will generate insights relevant to bio-ERW in soils or reactors.

• Weathering effects of individual microbes can be isolated from their function within a natural microbial community.

Related problem statements

• Platforms for high-throughput characterization of biologically-enhanced mineral weathering [38]

• Propose and assess microbial community functions for reactor-based bio-enhanced weathering [39]

• Design, TEA, and LCA of reactor-based bio-enhanced rock weathering [37]

• Functionally characterize microbial weathering processes in soil [34]

Other information

• This work would benefit from development of high-throughput platforms for assaying bio-enhanced weathering [38] and methods for systematic discovery of culture conditions for non-model microbes [40][41].

• To ensure measurements are comparable, total alkalinity generation should be measured. While cation release is also informative, different cations may be released at different and time-varying rates, so they are generally not a good measure of alkalinity generation [42][4][43].

• The goals of this problem statement are also relevant to improving foundational biological understanding for biomining [30].