Fig 1.
Schematic diagram of the bioelectrochemical set-up used in this work.
In the denominated bioelectrochemical system (BES) a working electrode (WE) is covered by a biofilm; CE and RE are immersed in the same solution (left). In the microbial fuel cell (MFC) the anode and cathode compartments were separated by a PEM (Nafion) membrane (right). N2 was filtered by a 0.22 μm membrane, as shown.
Fig 2.
Phylogenetic tree of RNV-4 strain and closely related species based on 16S rRNA.
The tree was constructed using the neighbor-joining method. The numbers at nodes indicate the percentages of occurrence of the branching order in 500 bootstrapped trees for values greater than 50%. Scale bar = 0.5% divergence.
Fig 3.
Morphology and colour of Dietzia sp. RNV-4.
(A) Pigment expression after 48-h incubation at 32°C on Brain-Heart Infusion Agar (BHI) and Luria-Bertani agar (LB) media (B) Picture of a colony in LB agar obtained with a digital microscope (40X).
Fig 4.
Electrochemical experiments performed with Dietzia sp. RNV-4, in the BES set-up.
(A) Chronoamperometry after the inoculation. The medium change is indicated as MC and the addition of lactate as L (see Materials and Methods, section Assembly and operation of the BES). The star indicates the time when the CV experiments were done. (B) CVs at different stages of growth day 0 (just before inoculation, black), day 2 (red), day 5 (blue), and day 7 (green) of growth in the BES, indicated with star in A. Scan rate 1 mV/s.
Table 1.
Carotenoids detected by HPLC method.
Fig 5.
Microphotography of the working electrode used in the BES in order to understand the morphology of the biofilm formed by Dietzia sp. RNV-4 on carbon paper electrodes.
(A) Electrode from a control experiment, 1000X, bar 20 μm, by SEM. (B) Biofilm of Dietzia sp. RNV-4, 1000X, bar 20 μm, by SEM. (C) Biofilm of Dietzia sp. RNV-4, 60X zoom 2.5, bar10 μm, by CLSM. (D) Biofilm of Dietzia sp. RNV-4, 60X zoom 2.5, by confocal microscopy. XYZ images were processed using the program Image J.
Fig 6.
MFC experiments and bacterial strain comparison.
(A) Current density vs. time measured from a MFCS (S. oneidensis MR-1, closed squares) and from a MFCD (Dietzia sp. RNV-4 (opened squares).n = 3, RL = 4.68 kΩ. (B) Power density curves from the MFCS (closed simbols squares) and MFCD (opened squares) made after 1 (solid line) and 4 (dash line) days incubation. (C) Comparison of polarization curves from the MFCS (closed squares) and MFCD (opened squares) made after 1 (solid line) and 4 (dash line) days incubation.