Christopher J. Tadanier

Measuring interfacial and adhesion forces between bacteria and mineral surfaces with biological force microscopy

Interfacial and adhesion forces between living, unmodified bacterial cells ( Escherichia coli) and mineral surfaces (muscovite, goethite, and graphite) have been directly measured in aqueous solution using a force microscope. Native cells are linked to a force-sensing probe that is used to characterize interactions as a mineral surface approaches, makes contact with, and withdraws from bacteria on the probe. Attractive and repulsive interfacial forces were detected at ranges up to 400 nanometers separation, the magnitude and sign depending on the ionic strength of the intervening solution and the mineral surface charge and hydrophobicity. Adhesion forces, up to several nanoNewtons in magnitude and exhibiting various fibrillation dynamics, were also measured and reflect the complex interactions of structural and chemical functionalities on the bacteria and mineral surfaces. Copyright

Ab Initio Determination of Edge Surface Structures for Dioctahedral 2 : 1 Phyllosilicates: Implications for Acid-Base Reactivity

The atomic structure of dioctahedral 2:1 phyllosilicate edge surfaces was calculated using pseudopotential planewave density functional theory. Bulk structures of pyrophyllite and ferripyrophyllite were optimized using periodic boundary conditions, after which crystal chemical methods were used to obtain initial terminations for ideal (110)- and (010)-type edge surfaces. The edge surfaces were protonated using various schemes to neutralize the surface charge, and total minimized energies were compared to identify which schemes are the most energetically favorable. The calculations show that significant surface relaxation should occur on the (110)-type faces, as well as in response to different protonation schemes on both surface types. This result is consistent with atomic force microscopy observations of phyllosilicate dissolution behavior. Bond-valence methods incorporating bond lengths from calculated structures can be used to predict intrinsic acidity constants for surface functional groups on (110)- and (010)-type edge surfaces. However, the occurrence of surface relaxation poses problems for applying current bond-valence methods. An alternative method is proposed that considers bond relaxation, and accounts for the energetics of various protonation schemes on phyllosilicate edges.

Dynamics of the Mineral?Microbe Interface: Use of Biological Force Microscopy in Biogeochemistry and Geomicrobiology

At the most fundamental level, inter- and intramolecular forces delineate the interface between a microorganism and a mineral surface. A new technique, termed biological force microscopy (BFM), is described that can be used to directly probe the dynamics of the mineral-microbe interface. BFM quantifies attractive and repulsive forces in the nano-Newton range between living microbial cells and mineral surfaces in aqueous solution. Native bacterial cells are linked to a force-sensor that is used in a force microscope to measure bacteria-mineral interactions as a function of the distance between the mineral surface and the cells on the sensor. The magnitudes and ranges of the measured forces reflect the chemical and structural intricacies of the mineral-microbe interface. BFM is presented with potential applications to studies assessing the role that microbes or biomolecules play in geochemical and mineralogical processes.At the most fundamental level, inter- and intramolecular forces delineate the interface between a microorganism and a mineral surface. A new technique, termed biological force microscopy (BFM), is described that can be used to directly probe the dynamics of the mineral-microbe interface. BFM quantifies attractive and repulsive forces in the nano-Newton range between living microbial cells and mineral surfaces in aqueous solution. Native bacterial cells are linked to a force-sensor that is used in a force microscope to measure bacteria-mineral interactions as a function of the distance between the mineral surface and the cells on the sensor. The magnitudes and ranges of the measured forces reflect the chemical and structural intricacies of the mineral-microbe interface. BFM is presented with potential applications to studies assessing the role that microbes or biomolecules play in geochemical and mineralogical processes.