Figure legends
Fig. 1. Phylogenetic tree of four bacterial isolates and
representatives of related species based on the 16S rRNA gene sequences.
The tree was inferred from an alignment of 1,380-bp-long sequences of
16S rRNA genes, and constructed by the neighbor-joining method. The
numbers at the nodes denote the bootstrap percentages derived from 1,000
replications. Scale bar: 0.01 substitutions per nucleotide position.
Fig. 2. Anaerobic growth of P. denitrificansMIC1-1T (A), P. denitrificans AT004 (B),P. denitrificans KGS048 (C), Prolixibacter sp. SD074 (D).Prolixibacter sp. NT017 (E), and
P. bellariivorans JCM 13498T (F). These strains
were grown anaerobically in either YSw medium (open symbol) or
ammonium-free YSw medium (closed symbol) in the presence (circle) or
absence (triangle) of 10 mM sodium nitrate. Data represent the means
(n = 3), with standard deviation values less than 18% of the
corresponding mean values.
Fig. 3. Scanning electron micrographs showing the surface and
cross-sections of Fe0 foils incubated anaerobically
with nitrate-reducing Prolixibacter strains.
Fe0 foils were incubated for 30 days in corrosion-test
medium in the presence of P. denitrificansMIC1-1T (A–C), P. denitrificans AT004 (D–F),P. denitrificans KG048 (G–I), and Prolixibacter sp. SD074
(J–L). A, D, G, and J: the surface of Fe0 foils (×300
magnification). B, E, H, and K: the surface of Fe0foils (×1,000 magnification). C, F, I, and L: the cross-section of
Fe0 foils (×300 magnification). Scale bar: 10 µm for
A, C, D, F, G, I, J, and L; 1 µm for B, E, H, and K. Scanning electron
micrographs were obtained from two independent experiments.
Fig. 4. Scanning electron micrographs showing the surface and
cross-sections of Fe0 foils incubated anaerobically
with nitrate-non-reducing Prolixibacter strains.
Fe0 foils were incubated for 30 days in corrosion-test
medium in the presence of Prolixibacter sp. NT017 (A–C), andP. belleriivorans JCM 13498T (D–F). The
aseptic controls are also shown (G–I). A, D, and G: the surface of
Fe0 foils (×300 magnification). B, E, and H: the
surface of Fe0 foils (×1,000 magnification). C, F, and
I: the cross-section of Fe0 foils (×300
magnification). Bar = 10 µm for A, C, D, F, G, and I. Scale bar: 1 µm
for B, E, and H. Scanning electron micrographs were obtained from two
independent experiments.
Fig. 5. Corrosion potential and corrosion current of an
Fe0 electrode immersed in the cultures of P.
denitrificans strain MIC1-1T and Prolixibactersp. NT017. Corrosion potential and corrosion current of an
Fe0 electrode were determined as described in the
Materials and Methods. (A) Change in the corrosion potential of an
Fe0 foil used as the working electrode. (B) Change in
the corrosion current generated at the Fe0 foil poised
at 25 mV versus corrosion potential. Solid red line: in the presence ofP. denitrificans MIC1-1T; dashed green line: in
the presence of Prolixibacter sp. strain NT017; dotted black
line, aseptic control.
Fig. 6. Nitrate reduction and the accumulation of nitrite and
ammonium in the cultures of nitrate-reducing Prolixibacterstrains. Nitrate-reducing Prolixibacter strains were grown under
an atmosphere of N2:CO2 (4:1) in
corrosion-test medium either in the presence (A to E) or absence (F to
J) of an Fe0 foil. In F to J, the concentrations of
oxidized iron in the aseptic controls were between 0 mM at day 0 and 0.2
mM at day 28. The strains used were P. denitrificansMIC1-1T (A and F), P. denitrificans AT004 (B
and G), P. denitrificans KGS048 (C and H) Prolixibactersp. SD074 (D and I), and aseptic control (E and J). Filled circle:
nitrate concentration, filled triangle: nitrite concentration, cross:
ammonium concentration, and open circles: concentration of oxidized
iron. Data represent means (n = 3), with standard deviation
values less than 8.9% of the corresponding mean values.
Fig. 7. The relationship between Fe0oxidation and nitrite reduction. The data in Fig. 6 are rearranged to
show the relationships between the increment in the concentration of
oxidized iron (open circles) and the consumed concentration of nitrite
(filled triangle) during three weeks after day 7. The latter
concentration was calculated as described in the text. The strains used
were P. denitrificans MIC1-1T (A), P.
denitrificans AT004 (B), P. denitrificans KGS048 (C), andProlixibacter sp. SD074 (D). Bold lines were obtained by
multiplying the values of the consumed concentration of nitrite bya where a = 1.25 for A, 2 for B, 2.4 for C, and 1.85 for D. Data
represent means (n = 3), with standard deviation values less than
8.9% of the corresponding mean values.
Table 1. Bacterial strains used in this study.