Real-Time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction.

Manganese oxides are often highly reactive and easily reduced, both abiotically, by a variety of inorganic chemical species, and biologically during anaerobic respiration by microbes. To evaluate the reaction mechanisms of these different reduction routes and their potential lasting products, we measured the sequence progression of microbial manganese(IV) oxide reduction mediated by chemical species (sulfide and ferrous iron) and the common metal-reducing microbe Shewanella oneidensis MR-1 under several endmember conditions, using synchrotron X-ray spectroscopic measurements complemented by X-ray diffraction and Raman spectroscopy on precipitates collected throughout the reaction. Crystalline or potentially long-lived phases produced in these experiments included manganese(II)-phosphate, manganese(II)-carbonate, and manganese(III)-oxyhydroxides. Major controls on the formation of these discrete phases were alkalinity production and solution conditions such as inorganic carbon and phosphate availability. The formation of a long-lived Mn(III) oxide appears to depend on aqueous Mn(2+) production and the relative proportion of electron donors and electron acceptors in the system. These real-time measurements identify mineralogical products during Mn(IV) oxide reduction, contribute to understanding the mechanism of various Mn(IV) oxide reduction pathways, and assist in interpreting the processes occurring actively in manganese-rich environments and recorded in the geologic record of manganese-rich strata.

Burkholderia insulsa sp. nov., a facultatively chemolithotrophic bacterium isolated from an arsenic-rich shallow marine hydrothermal system.

Enrichment cultures inoculated with hydrothermally influenced nearshore sediment from Papua New Guinea led to the isolation of an arsenic-tolerant, acidophilic, facultatively aerobic bacterial strain designated PNG-April(T). Cells of this strain were Gram-stain-negative, rod-shaped, motile and did not form spores. Strain PNG-April(T) grew at temperatures between 4 °C and 40 °C (optimum 30-37 °C), at pH 3.5 to 8.3 (optimum pH 5-6) and in the presence of up to 2.7% NaCl (optimum 0-1.0%). Both arsenate and arsenite were tolerated up to concentrations of at least 0.5 mM. Metabolism in strain PNG-April(T) was strictly respiratory. Heterotrophic growth occurred with O2 or nitrate as electron acceptors, and aerobic lithoautotrophic growth was observed with thiosulfate or nitrite as electron donors. The novel isolate was capable of N2-fixation. The respiratory quinones were Q-8 and Q-7. Phylogenetically, strain PNG-April(T) belongs to the genus Burkholderia and shares the highest 16S rRNA gene sequence similarity with the type strains of Burkholderia fungorum (99.8%), Burkholderia phytofirmans (98.8%), Burkholderia caledonica (98.4%) and Burkholderia sediminicola (98.4%). Differences from these related species in several physiological characteristics (lipid composition, carbohydrate utilization, enzyme profiles) and DNA-DNA hybridization suggested the isolate represents a novel species of the genus Burkholderia, for which we propose the name Burkholderia insulsa sp. nov. The type strain is PNG-April(T) ( = DSM 28142(T) = LMG 28183(T)).