Understanding the Complexity of Biogenic Mineral Formation in Microbial Extracellular Polymeric Substances: a 3-d Nano-scale Perspective
EMSL Project ID
51000
Abstract
Microbial role in sequestration of various metal has been well studied, including PNNL Microbiology group and numerous EMSL user projects. However, the current view of microbial-mineral interactions at high resolution has arisen from 2-dimensional images of 3-dimensional structures. Countless structures that appeared to have linear ultrastructure in a single cross-section had proven to actually have a robust 3d structure that had often posed unpredictable functional consequences. Based on our previous research several years ago, we discovered that our model organism for metal reduction, Shewanella oneidensis MR-1, produced copious amounts for extracellular polymeric substances (EPS) during its anaerobic respiration of uranium [1, 2]. Bacterially-secreted EPS, forming the matrix of microbial biofilms, present a remarkable dynamic entity. Although it is generally assumed that EPS’s primary function is physical adhesiveness which plays a major role in biofilm formation and cell adhesion to solid surfaces, its other properties, such as high absorptive capacity, are also important, yet often overlooked. Generally composed of bacterially secreted heterogeneous combinations of high-molecular-weight polysaccharides, lipids, proteins, and nucleic acids, as well as variable amounts of structural components, it provides an assortment of functional groups that are capable of binding, accumulating, and sequestering dissolved organic matter and metals from the environment. In our experiments with uranium, EPS was associated with large amounts of biogenically-produced nanocrystalline UO4.
We hypothesize that EPS plays a key role in metal nucleation, capture and precipitation and, possibly, extracellular electron transfer. Furthermore, after the cell lysis, membrane lipid fractions and intracellular material gets incorporated into the overall polysaccharide network, and its functional groups provide a substrate for nucleation of new biominerals. Therefore, understanding how microbial EPS functions and interacts with inorganic substrates such as metal ions and mineral surfaces connects the molecular-scale biochemical processes to those at the microorganism-level. Importantly, EPS can present itself as a currently not-recognized redox vehicle for metal sequestration from solutions.
We would like to obtain representative data to identify common features and make implications that will be important for strengthening our understanding of how microbes interact with redox transformable metals, valuable for research including industrial applications (the above-mentioned rare earth elements sequestration), and biogeochemical reactions, by providing insight to how microorganisms influence processes at larger scales in soil environments.
Project Details
Start Date
2019-06-18
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)