Microbial Populations of the River-Recharged Fredericton Aquifer

The City of Fredericton, New Brunswick, Canada obtains its water from the Saint John River-recharged Fredericton aquifer. Water quality improves as it flows from the river into the aquifer in a process called bank filtration. Microorganisms contribute to water quality improvements during bank filtration by removing organic carbon. In the Fredericton aquifer, microbially catalyzed reductive dissolution of manganese oxide minerals negatively affects water quality. Aerobic and anaerobic microorganisms were cultured from Fredericton aquifer production well water, from associated bedrock groundwater, and from Saint John River sediment core and sediment groundwater samples. Aerobes were the largest culturable groups in all samples. The ratio of aerobes to other microbial groups, i.e., those reducing nitrate, Mn^{4 +}, Fe^{3 +}, or sulfate, did not vary significantly along the water flow path from the river to the aquifer. Analysis of microbial community composition along the flow path indicated an essentially identical community except in the immediate vicinity of the aquifer. This is in agreement with the absence of macroscale redox zones in the sediment below the Saint John River as determined by groundwater geochemical data. Bacteria isolated from groundwater samples, identified by 16S ribosomal RNA gene sequencing, were α -, β -, γ -, and δ -Proteobacteria, Actinobacteria, and Firmicutes. In contrast to groundwater samples, the majority of bacteria isolated from sediments were γ -Proteobacteria. Numbers of manganese-reducing bacteria, including Aeromonas spp., were small, however Mn^{4 +} reduction ability was widespread in bacteria enriched and isolated with other electron acceptors. The diverse Fredericton aquifer microbial community likely uses manganese oxide minerals as a sink for electrons derived from organic carbon oxidation.     

Membrane topology of the methyl-accepting chemotaxis protein DcrA fromDesulfovibrio vulgaris Hildenborough

Alkaline phosphatase fusions were used to study the membrane topology of DcrA, a protein of 668 amino acids fromDesulfovibrio vulgaris Hildenborough, which has two potentially membrane-spanning hydrophobic sequences at residues 11 to 29 and 188 to 207. A fusion at amino acid residue 170 in the proposed periplasmic domain exhibited high alkaline phosphatase activity, while low activity was observed for a fusion at amino acid residue 284 in the proposed cytoplasmic domain. The data support a topological model for DcrA similar to that of the methyl-accepting chemotaxis proteins of the enteric bacteria.