Electron Acceptor-Dependent Respiratory and Physiological Stratifications in Biofilms

Bacterial respiration is an essential driving force in biogeochemical cycling and bioremediation processes. Electron acceptors respired by bacteria often have solid and soluble forms that typically coexist in the environment. It is important to understand how sessile bacteria attached to solid electron acceptors respond to ambient soluble alternative electron acceptors. Microbial fuel cells (MFCs) provide a useful tool to investigate this interaction. In MFCs with Shewanella decolorationis, azo dye was used as an alternative electron acceptor in the anode chamber. Different respiration patterns were observed for biofilm and planktonic cells, with planktonic cells preferred to respire with azo dye while biofilm cells respired with both the anode and azo dye. The additional azo respiration dissipated the proton accumulation within the anode biofilm. There was a large redox potential gap between the biofilms and anode surface. Changing cathodic conditions caused immediate effects on the anode potential but not on the biofilm potential. Biofilm viability showed an inverse and respiration-dependent profile when respiring with only the anode or azo dye and was enhanced when respiring with both simultaneously. These results provide new insights into the bacterial respiration strategies in environments containing multiple electron acceptors and support an electron-hopping mechanism within Shewanella electrode-respiring biofilms

Performance of the MRIS for domestic wastewater treatment.

<p>(A) The concentration of chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (NH₃-N), nitrate nitrogen (NO₃-N); (B) Dissolved oxygen (DO) concentration (the right axis) and pH value (the left axis) in the Inlet, Sampling ports and the Outlet. A1–5: the Inlet, Sampling port 1–3, and the Outlet, correspondingly.</p

The copy numbers of AOB and AOA <i>amo</i>A genes from the flowing (A) and the stationary phase (B).

<p>All data are the means of values obtained from three parallel experiments ± SD (<i>t</i>-test, <i>p</i><0.01) using the ΔΔCT method. A1–5: the Inlet, Sampling port 1–3, and the Outlet, correspondingly; P1–8: Packing 1–8, correspondingly.</p

PBDE congener products of BDE-209 after 70 days performance by c-MFCs and o-MFCs.

<p>PBDE congener products of BDE-209 after 70 days performance by c-MFCs and o-MFCs.</p

Novel Strategy for Tracking the Microbial Degradation of Azo Dyes with Different Polarities in Living Cells

Direct visualization evidence is important for understanding the microbial degradation mechanisms. To track the microbial degradation pathways of azo dyes with different polar characterizations, sensors based on the fluorescence resonance energy transfer (FRET) from 1,8-naphthalimide to azo dyes were synthesized, in which the quenched fluorescence will recover when the azo bond was cleaved. In living cells, the sensor-tracking experiment showed that the low polarity and hydrophobic azo dye can be taken up into the cells and reduced inside the cells, whereas the high polarity and hydrophilic azo dye can be reduced only outside the cells because of the selective permeability of the cell membranes. These results indicated that there were two different bacterial degradation pathways available for different polarity azo dyes. To our knowledge, no fluorescent sensor has yet been designed for illuminating the microbial degradation mechanisms of organic pollutants with different characteristics

The normalized signal intensity of the detected key gens families (A) and the organisms (B) involved in energy transformation process under both c-MFCs and o-MFCs.

<p>The signal intensities were the sum of detected individual gene sequences for each functional gene, averaged among three samples. All data are presented as mean±SE. **<i>p</i><0.05, *<i>p</i><0.10.</p

Phylogenetic analysis of 16S rRNA genes.

<p>Phylogenetic tree was constructed using the Neighbor-Joining method by MEGA v4.0.2 software. The numbers at the nodes are bootstrap values (<i>n</i> = 1000) and the Random seed value is 64,238.</p

The normalized signal intensity of the detected key gens families involved in aromatic compound degradation (A) and chlorinated solvent remediation (B) under both c-MFCs and o-MFCs.

<p>The signal intensities were the sum of detected individual gene sequences for each functional gene, averaged among three samples. All data are presented as mean±SE. *** <i>p</i><0.001, **<i>p</i><0.05, *<i>p</i><0.10.</p

Triplot of RDA for AOB in the flowing phase.

<p>The first and the second axes explained 76.8% and 6.8% of the total variation respectively. The length of each arrow is correlated with the degree of relationship between the response variables. The arrows point in the direction of the maximum change for the associated variable. Open symbols represent samples from the flowing phase.</p

Cluster analysis of functional genes detected using GeoChip 4.0.

<p>The figure was generated using CLUSTER and visualized in TREEVIEW. Black indicates signal intensities below the threshold value and red indicates a positive hybridization signal. The color intensity indicates differences in signal intensity. The samples from c-MFCs and o-MFCs on day 70 were clearly separated in two groups. Six different gene patterns were observed and indicated by numbers in the tree (A), and also illustrated in the graphs (B). (c1, c2, c3 represented the three replications of c-MFCs and o-1, o-2, o-3 represented those from o-MFCs.).</p