2000 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 1999 – JUN 2000
Biological Influences on Weathering
Biological activity can generate minerals with unique compositions, structures, and forms that may persist long after organic remains of cells associated with biomineralization are destroyed. Thus, laboratory studies of mineralization on, or in proximity to, organic polymer assemblages are of direct relevance to interpretation of biosignatures. We are exploring the linkages between structure and properties of organic polymers (such as those associated with cell surfaces), solution chemistry, and the resulting mineral-polymer composites. Biomimetic experiments are being conducted on iron oxyhydroxide- polymer systems where the iron oxyhydroxides is ferrihydrite or goethite (FeOOH). The work has required development of a number of new biomimetic composite materials that have been synthesized through such strategies as carbohydrate self-assembly, multiphase amphiphilic self-organization, and “guest-host” inorganic phase formation. Two- and three-dimensional matrices-templates based on natural functional polysaccharides were observed to host the formation of iron (III)-containing oxo-hydroxyphases of various morphologies. Close connection between polymer matrices and mesoscopic mineral phase morphologies was revealed in some cases. This work is primarily being conducted by Dr. Maria Nesterova, who joined our group shortly after the NASA funding became available in November 1999. She will present an invited talk at AGU that reports the results of the first 5 months of her work.
In parallel with the above mentioned laboratory studies, high-resolution and analytical transmission electron microscopy are being used to study biomineralized sheaths and stalks of a variety of iron-oxidizing microorganisms that form in a subsurface aquifer. All sheaths were heavily mineralized by ferric iron minerals, especially ferrihydrite and feroxyhite. Bacterially-mediated ferrous iron oxidation is followed by immediate precipitation due to the extremely low solubility of ferric iron at pH ~8.0. The resulting particle size is extremely small, typically 2-3 nm. Particles coat all polymer surfaces, leading to distinctive polymer-mineral assemblages, and form colloidal aggregates due to flocculation of nanoparticles in solution.
In addition to understanding the ways in which biomineralization occurs, it is important to understand how subsequent reactions (due to heat and / or time) can modify mineralogical biosignatures. This is especially important when particle size is very small, because the large driving force associated with surface free energy promotes rapid crystal growth. Characterization of the mineralized sheaths and stalks, as well as the colloidal aggregates of nanoparticles, demonstrated that crystal growth occurs primarily by a novel mechanism that involves oriented attachment of very small particles. This is most pronounced at the margins of polymers, where rotation of particles is not restricted by binding to the polymeric substrate. These findings lead to the prediction that the preexistence of cell and distinctive cell product morphologies might be detected via particle size distribution pattern analysis and defect microstructure analysis (the organic substrate should be evident due to the finer particle size). This research has been submitted for publication and will be published following some revision (Banfield et al. Science, in press).
In related work, Mr. Jeffrey Brownson, a MS student, also joined our group in Fall 1999 is working on experimental biomineralization of clay minerals on cell surfaces.
PROJECT MEMBERS:Jill Banfield
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Define how ecophysiological processes structure microbial communities, influence their adaptation and evolution, and affect their detection on other planets.
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet.