Eloise I. Larsen

Manganese(II) adsorption and oxidation by whole cells and a membrane fraction of Pedomicrobium sp. ACM 3067

Abstract Heat treatment of Pedomicrobium sp. ACM 3067 enhanced the adsorption of Mn(II) to whole cells but abolished Mn(II)-oxidising activity. In whole cells, optimal Mn(II)-oxidising activity occurred at pH 7 and 25 °C. The apparent Km of the Mn(II)-oxidising system for Mn(II) was 26 μM. These data confirm that Mn(II) oxidation is an enzymic process in Pedomicrobium sp. ACM 3067. Measurement of Mn(II) oxidation during the growth cycle demonstrated that the highest activity occurred during early- to mid-exponential phase and was independent of the presence of Mn in the growth medium. Mn(II)-oxidising activity was localised to the membrane fraction. Transmission electron microscopy showed that this fraction consisted of double-layered membrane vesicles. Positively charged molecules such as poly-l-lysine interfered with the adsorption and oxidation of Mn(II) by whole cells and membranes. Similarly, aminoglycoside antibiotics such as gentamicin sulfate proved to be potent inhibitors of Mn(II) oxidation. Treatment of cells with the copper chelator diethyldithiocarbamate inhibited Mn(II) oxidation. Enzyme activity was restored by the addition of Cu(II) ions, but not by Co(II) nor Zn(II). We conclude that Mn(II) oxidation in Pedomicrobium sp. ACM 3067 is catalysed by a Cu-dependent enzyme.

Neutrophilic, Microaerophilic Fe(II)-Oxidizing Bacteria are Ubiquitous in Aquatic Habitats of a Subtropical Australian Coastal Catchment (Ubiquitous FeOB in Catchment Aquatic Habitats)

We examined the abundance and distribution of neutrophilic, microaerophilic Fe(II)-oxidizing bacteria (FeOB) in aquatic habitats of a highly weathered, subtropical coastal catchment where Fe biogeochemistry is of environmental significance. Laboratory cultivation and microscopy indicated that stalked Gallionella and sheathed Leptothrix-like FeOB were present in microbial mats associated with a circumneutral-pH, groundwater seep and streambank surface sediment, whereas unicellular FeOB were widespread in surface and subsurface waters, including a seep, shallow stream and estuary-adjacent groundwater. Direct Gallionella-specific PCR detected dominant bacterial members related to Sideroxydans paludicola (95% sequence identity, SI) and Gallionella capsiferriformans (96% SI) in the seep microbial mat. TGGE analysis indicated that the most common FeOB in water enrichment cultures were related to S. lithotrophicus (96% SI). The ubiquity of FeOB in Poona catchment aquatic habitats suggests bacterial Fe(II) oxidation is integral to catchment Fe biogeochemistry.