Competition between Fe(III)-Reducing and Methanogenic Bacteria for Acetate in Iron-Rich Freshwater Sediments

• Published in: Microbial ecology 2003-03, Vol.45 (3), p.252-258
• Main Authors: E. E. Roden, Wetzel, R. G.
• Format: Article
• Language: English
• Subjects: Acetates; Acetates - metabolism; Anaerobiosis; Bacteria; Biological and medical sciences; Carbon; Euryarchaeota - metabolism; Ferric Compounds - metabolism; Fresh water; Fresh Water - microbiology; Freshwater; Fundamental and applied biological sciences. Psychology; Geologic Sediments - microbiology; Iron; Juncus effusus; Kinetics; Metabolism; Methane production; Methanobacterium formicicum; Microbiology; Organic carbon; Oxides; Sediments; Slurries; Soil Microbiology; Sulfates
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/s00248-002-1037-9

The kinetics of acetate uptake and the depth distribution of$[2\text{-}{}^{14}{\rm C}]\text{acetate}$metabolism were examined in iron-rich sediments from a beaver impoundment in northcentral Alabama. The half-saturation constant (Km) determined for acetate uptake in slurries of Fe(III)-reducing sediment (0.8 μM) was more than 10-fold lower than that measured in methanogenic slurries (12 μM) which supported comparable rates of bulk organic carbon metabolism and Vmaxvalues for acetate uptake. The endogenous acetate concentration ($S_{{\rm n}}$) was also substantially lower (1.7 μM) in Fe(III)-reducing vs methanogenic (9.0 μM) slurries. The proportion of$[2\text{-}{}^{14}{\rm C}]\text{acetate}$converted to^{14}{\rm CH}{}_{4}$increased with depth from ca 0.1 in the upper 0.5 cm to ca 0.8 below 2 cm and was inversely correlated (r2=0.99) to a decline in amorphous Fe(III) oxide concentration. The results of the acetate uptake kinetics experiments suggest that differences in the affinity of Fe(III)-reducing bacteria vs methanogens for acetate can account for the preferential conversion of$[2\text{-}{}^{14}{\rm C}]\text{acetate}$to14CO2in Fe(III) oxide-rich surface sediments, and that the downcore increase in conversion of$[2\text{-}{}^{14}{\rm C}]\text{acetate}$to^{14}{\rm CH}{}_{4}$can be attributed to progressive liberation of methanogens from competition with Fe(III) reducers as Fe(III) oxides are depleted with depth.