No abstract

X-ray diffraction (XRD) and Mn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy were combined to elaborate a structural model for phyllomanganates (layer-type Mn oxide) lacking 3D ordering (turbostratic stacking). These techniques were applied to a sample produced by a common soil and freshwater bacterium (Pseudomonas putida) and to two synthetic analogs, δ-MnO 2 and "acid birnessite", obtained by the reduction of potassium permanganate with MnCl 2 and HCl, respectively. To interpret the diffraction and spectroscopic data, we applied an XRD simulation technique utilized previously for wellcrystallized birnessite varieties, complementing this approach with single-scattering-path simulations of the Mn K-edge EXAFS spectra. Our structural analyses revealed that all three Mn oxides have an hexagonal layer symmetry with layers comprising edge-sharing Mn 4+ O 6 octahedra and cation vacancies, but no layer Mn 3+ O 6 octahedra. The proportion of cation vacancies in the layers ranged from 6 to 17 %, these vacancies being charge-compensated in the interlayer by protons, alkali metals, and Mn atoms, in amounts that vary with the phyllomanganate species and synthesis medium. Both vacancies and interlayer Mn were

Viruses are the most abundant biological entities in the oceans and a pervasive cause of mortality of microorganisms that drive biogeochemical cycles. Although the ecological and evolutionary

In contrast, pMn showed no gravitational settling behavior (Figures 1, 4b). Instead, peak 116 pMn concentrations remained close in depth to dMn and 3 He xs and followed density surfaces, 117 indicative of isopycnal mixing. Thus, while most pMn and pFe are removed exponentially from (Figures 1, S1). 159The physicochemical form of hydrothermal dissolved iron -A key finding of this study, 160 not discussed previously 8 but critical to the fate of Fe in the SEPR hydrothermal plume, is that 161 the maximum dissolved Fe also deepens by ~350 m by Sta. 36, mimicking pFe (Figures 1, 4a). is not isotopically resolvable in the near-field plume (dFe >5 nM). would not apply to dMn because dMn is minimally complexed by organic matter in natural 233 waters 2 , and negligible Mn was observed in the colloidal fraction ( Figure S4).

Oceanic crust comprises the largest hydrogeologic reservoir on Earth, containing fluids in thermodynamic disequilibrium with the basaltic crust. Little is known about microbial ecosystems that inhabit this vast realm and exploit chemically favorable conditions for metabolic activities. Crustal samples recovered from ocean drilling operations are often compromised for microbiological assays, hampering efforts to resolve the extent and functioning of a subsurface biosphere. We report results from the first in situ experimental observatory systems that have been used to study subseafloor life. Experiments deployed for 4 years in young (3.5 Ma) basaltic crust on the eastern flank of the Juan de Fuca Ridge record a dynamic, post-drilling response of crustal microbial ecosystems to changing physical and chemical conditions. Twisted stalks exhibiting a biogenic iron oxyhydroxide signature coated the surface of mineral substrates in the observatories; these are biosignatures indicating colonization by iron oxidizing bacteria during an initial phase of cool, oxic, iron-rich conditions following observatory installation. Following thermal and chemical recovery to warmer, reducing conditions, the in situ microbial structure in the observatory shifted, becoming representative of natural conditions in regional crustal fluids. Firmicutes, metabolic potential of which is unknown but may involve N or S cycling, dominated the post-rebound bacterial community. The archaeal community exhibited an extremely low diversity. Our experiment documented in situ conditions within a natural hydrological system that can pervade over millennia, exemplifying the power of observatory experiments for exploring the subsurface basaltic biosphere, the largest but most poorly understood biotope on Earth.