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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 [26]. Acquisition of such data is hampered by low experimental throughput: previous studies have examined only one or a few specific microbe-mineral pairings (e.g., [16][11][27][28][29]), with one group systematically screening genes in one organism [30][31]. Novel methods are needed for rapidly measuring the weathering activity of microbe-mineral pairings and screening genetic variants in high throughput.

Actionable Goals

Platforms should be developed for high-throughput measurement of microbially-enhanced weathering in the lab. Enabling capabilities would include parallel screening of weathering by many genetic variants [31]; screening weathering enhancement by microbial exudates, in isolation from cells or biofilms that might influence diffusion; and streamlined, intercomparable assays of weathering by diverse microbial species. Measurements would ideally be miniaturized (i.e., in sub-ml volumes). To be comparable, measurements should rely on total alkalinity generation rather than release of specific cations, since different cations may be released at different and time-varying rates [32][33][4]. To be most application-relevant, weathering rates would ideally be measured over weeks or longer, since rates can change over time, for example due to passivation layer formation [4]. Integration of Raman spectroscopy would be valuable for measuring mineralogical changes [34].

Additional information

Open Questions

• The goals could be clarified by providing a starting list of specific microbe-mineral pairings worth screening.

• Identification and development of rapid assays for high-throughput screening. 

• New computational tools to make sense of the data we get from these screens.

Assumptions

• 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

• Propose and assess microbial community functions for reactor-based bio-enhanced weathering [35]

• Systematically characterize microbially-enhanced mineral weathering [26]

• Design, TEA, and LCA of reactor-based bio-enhanced rock weathering [36]

• Functionally characterize microbial weathering processes in soil [37]

Other information

• In addition to lab-based characterization of bioweathering, field-based characterization is also needed [9][37]

• The goals of this problem statement are also relevant to improving foundational biological understanding for biomining [31].