|Schellenberger, S; Drake, HL; Kolb, S: Functionally Redundant Cellobiose-Degrading Soil Bacteria Respond Differentially to Oxygen, Applied and Environmental Microbiology, 77, 6043-6048 (2011)|
The availability of oxygen (O2) in aerated (i.e., water-unsaturated) soils affects the metabolic activity of aerobic and anaerobic soil prokaryotes that degrade plant-derived saccharides. Fluctuating availabilities of O2 were imposed on agricultural soil slurries supplemented with cellobiose. Slurries were subjected to oxic conditions (48 hours), followed by an anoxic period (120 hours) and a final oxic period (24 hours). Redox potential was stable at 500 mV during oxic periods but rapidly (within 10 hours) decreased under anoxic conditions to -330 mV. The consumption of cellobiose occurred without apparent delay at all redox potentials. Metabolic activity of seven, previously identified saccharolytic family-level taxa of the investigated soil were measured with newly designed quantitative PCR assays targeting the 16S ribosomal RNA. Four taxa responded to the experimental conditions. The amount of ribosomal RNA of Micrococcaceae and Cellulomonadaceae (Actinobacteria) increased under oxic conditions. In contrast, the RNA content of Clostridiaceae (Cluster I, Firmicutes), and two uncultured family-level-taxa, i.e., ‘Cellu’ and ‘Sphingo’ (both Bacteroidetes), increased under anoxic conditions. That the degradation of cellobiose was independent of the availability of O2 and that redox potentials decreased in response to anaerobic activities indicated that the degradation of cellobiose was linked to functionally redundant cellobiose-degrading taxa capable of altering redox conditions.
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