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Fe biomineralization mirrors individual metabolic activity in a nitrate-dependent Fe(II)-oxidizer.

Miot J, Remusat L, Duprat E, Gonzalez A, Pont S, Poinsot M - Front Microbiol (2015)

Bottom Line: Mineral precipitation within the periplasm is, however, thought to induce death, as a result of permeability loss preventing nutrient and waste transit across the cell wall.Carbon assimilation decreased exponentially with increasing cell-associated Fe content.Eventually, our results suggest that periplasmic Fe biomineralization may provide a signature of individual metabolic status, which could be looked for in the fossil record and in modern environmental samples.

View Article: PubMed Central - PubMed

Affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d'Histoire Naturelle, Université Pierre et Marie Curie - Sorbonne Universités, CNRS UMR 7590, IRD 206 Paris, France.

ABSTRACT
Microbial biomineralization sometimes leads to periplasmic encrustation, which is predicted to enhance microorganism preservation in the fossil record. Mineral precipitation within the periplasm is, however, thought to induce death, as a result of permeability loss preventing nutrient and waste transit across the cell wall. This hypothesis had, however, never been investigated down to the single cell level. Here, we cultured the nitrate reducing Fe(II) oxidizing bacteria Acidovorax sp. strain BoFeN1 that have been previously shown to promote the precipitation of a diversity of Fe minerals (lepidocrocite, goethite, Fe phosphate) encrusting the periplasm. We investigated the connection of Fe biomineralization with carbon assimilation at the single cell level, using a combination of electron microscopy and Nano-Secondary Ion Mass Spectrometry. Our analyses revealed strong individual heterogeneities of Fe biomineralization. Noteworthy, a small proportion of cells remaining free of any precipitate persisted even at advanced stages of biomineralization. Using pulse chase experiments with (13)C-acetate, we provide evidence of individual phenotypic heterogeneities of carbon assimilation, correlated with the level of Fe biomineralization. Whereas non- and moderately encrusted cells were able to assimilate acetate, higher levels of periplasmic encrustation prevented any carbon incorporation. Carbon assimilation only depended on the level of Fe encrustation and not on the nature of Fe minerals precipitated in the cell wall. Carbon assimilation decreased exponentially with increasing cell-associated Fe content. Persistence of a small proportion of non-mineralized and metabolically active cells might constitute a survival strategy in highly ferruginous environments. Eventually, our results suggest that periplasmic Fe biomineralization may provide a signature of individual metabolic status, which could be looked for in the fossil record and in modern environmental samples.

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Related in: MedlinePlus

13C assimilation as a function of the level of biomineralization. (A,B)16O and 12C14N NanoSIMS images of a control culture never exposed to biomineralization medium. (C–E) Carbon assimilation by mineralized cells. (C,D)16O and 13C14N/12C14N NanoSIMS images of bacteria cultured 1 day in the Gt-medium, then transferred for 1 day in the labeled medium (same area analyzed in the two maps). Red, green, and yellow data points in panel (E) correspond to the bacteria identified by the color circles in panels (C,D). Their 16O/CN and 13C14N/12C14N ratios are (0.429; 0.148), (0.129; 0.255), and (0.598; 0.196), respectively. (E)13C14N/12C14N as a function of 16O/CN ratios in all mineralized populations of all samples studied (whatever the biomineralization and incubation conditions – see red points in Figure 6). The 3-parameter exponential model, estimated by non-linear least-square fitting, is displayed as a red curve (R2 = 0.397).
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Figure 4: 13C assimilation as a function of the level of biomineralization. (A,B)16O and 12C14N NanoSIMS images of a control culture never exposed to biomineralization medium. (C–E) Carbon assimilation by mineralized cells. (C,D)16O and 13C14N/12C14N NanoSIMS images of bacteria cultured 1 day in the Gt-medium, then transferred for 1 day in the labeled medium (same area analyzed in the two maps). Red, green, and yellow data points in panel (E) correspond to the bacteria identified by the color circles in panels (C,D). Their 16O/CN and 13C14N/12C14N ratios are (0.429; 0.148), (0.129; 0.255), and (0.598; 0.196), respectively. (E)13C14N/12C14N as a function of 16O/CN ratios in all mineralized populations of all samples studied (whatever the biomineralization and incubation conditions – see red points in Figure 6). The 3-parameter exponential model, estimated by non-linear least-square fitting, is displayed as a red curve (R2 = 0.397).

Mentions: Nano-Secondary Ion Mass Spectrometry analyses indicate that co-existence of mineralized and non-mineralized cells persisted after 4 days in the labeled medium, whatever the biomineralization conditions previously experienced (Figures 3 and 4). Based on the maximum value of 16O/CN (where CN = 12C14N + 13C14N) recorded on a control culture that was prepared without Fe in an unlabeled medium (Figures 4A,B), we defined a 16O/CN ratio threshold (16O/CN = 0.121) above which cells were considered mineralized and below which they were defined as non-mineralized. In the following, quantitative analyses are based on this 16O/CN threshold. Cells at early stages of biomineralization exhibit a 16O level much higher than cells from the control culture (see e.g., cells circled in red, green, and yellow in Figures 4C,D). We estimated the proportion of mineralized vs. non-mineralized cells based on the number of ROIs that exhibited 16O/CN ratios above and below the threshold, respectively (Supplementary Table S1, Figure 5). The values obtained must be interpreted cautiously as they were not compared with bulk measurements. General trends can, however, be described. The proportion of mineralized cells decreased with increasing time spent in the labeled medium. Significant differences were, however, observed depending on the biomineralization conditions. Proportion of mineralized cells decreased from 77 to 37% and from 88 to 13% in samples from FeP- and Gt-media, respectively, after only 1 day in the labeled medium. By comparison, proportion of mineralized cells remained constant (around 100%) in samples from Lp- and Mt-media at tlab = 1 day. In these samples, the main drop in the number of mineralized cells occurred between tlab = 1 and 4 days. After 4 days in the labeled medium, whatever the biomineralization conditions, all samples were mainly composed of non-mineralized cells (around or less than 20% of mineralized cells remaining).


Fe biomineralization mirrors individual metabolic activity in a nitrate-dependent Fe(II)-oxidizer.

Miot J, Remusat L, Duprat E, Gonzalez A, Pont S, Poinsot M - Front Microbiol (2015)

13C assimilation as a function of the level of biomineralization. (A,B)16O and 12C14N NanoSIMS images of a control culture never exposed to biomineralization medium. (C–E) Carbon assimilation by mineralized cells. (C,D)16O and 13C14N/12C14N NanoSIMS images of bacteria cultured 1 day in the Gt-medium, then transferred for 1 day in the labeled medium (same area analyzed in the two maps). Red, green, and yellow data points in panel (E) correspond to the bacteria identified by the color circles in panels (C,D). Their 16O/CN and 13C14N/12C14N ratios are (0.429; 0.148), (0.129; 0.255), and (0.598; 0.196), respectively. (E)13C14N/12C14N as a function of 16O/CN ratios in all mineralized populations of all samples studied (whatever the biomineralization and incubation conditions – see red points in Figure 6). The 3-parameter exponential model, estimated by non-linear least-square fitting, is displayed as a red curve (R2 = 0.397).
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Figure 4: 13C assimilation as a function of the level of biomineralization. (A,B)16O and 12C14N NanoSIMS images of a control culture never exposed to biomineralization medium. (C–E) Carbon assimilation by mineralized cells. (C,D)16O and 13C14N/12C14N NanoSIMS images of bacteria cultured 1 day in the Gt-medium, then transferred for 1 day in the labeled medium (same area analyzed in the two maps). Red, green, and yellow data points in panel (E) correspond to the bacteria identified by the color circles in panels (C,D). Their 16O/CN and 13C14N/12C14N ratios are (0.429; 0.148), (0.129; 0.255), and (0.598; 0.196), respectively. (E)13C14N/12C14N as a function of 16O/CN ratios in all mineralized populations of all samples studied (whatever the biomineralization and incubation conditions – see red points in Figure 6). The 3-parameter exponential model, estimated by non-linear least-square fitting, is displayed as a red curve (R2 = 0.397).
Mentions: Nano-Secondary Ion Mass Spectrometry analyses indicate that co-existence of mineralized and non-mineralized cells persisted after 4 days in the labeled medium, whatever the biomineralization conditions previously experienced (Figures 3 and 4). Based on the maximum value of 16O/CN (where CN = 12C14N + 13C14N) recorded on a control culture that was prepared without Fe in an unlabeled medium (Figures 4A,B), we defined a 16O/CN ratio threshold (16O/CN = 0.121) above which cells were considered mineralized and below which they were defined as non-mineralized. In the following, quantitative analyses are based on this 16O/CN threshold. Cells at early stages of biomineralization exhibit a 16O level much higher than cells from the control culture (see e.g., cells circled in red, green, and yellow in Figures 4C,D). We estimated the proportion of mineralized vs. non-mineralized cells based on the number of ROIs that exhibited 16O/CN ratios above and below the threshold, respectively (Supplementary Table S1, Figure 5). The values obtained must be interpreted cautiously as they were not compared with bulk measurements. General trends can, however, be described. The proportion of mineralized cells decreased with increasing time spent in the labeled medium. Significant differences were, however, observed depending on the biomineralization conditions. Proportion of mineralized cells decreased from 77 to 37% and from 88 to 13% in samples from FeP- and Gt-media, respectively, after only 1 day in the labeled medium. By comparison, proportion of mineralized cells remained constant (around 100%) in samples from Lp- and Mt-media at tlab = 1 day. In these samples, the main drop in the number of mineralized cells occurred between tlab = 1 and 4 days. After 4 days in the labeled medium, whatever the biomineralization conditions, all samples were mainly composed of non-mineralized cells (around or less than 20% of mineralized cells remaining).

Bottom Line: Mineral precipitation within the periplasm is, however, thought to induce death, as a result of permeability loss preventing nutrient and waste transit across the cell wall.Carbon assimilation decreased exponentially with increasing cell-associated Fe content.Eventually, our results suggest that periplasmic Fe biomineralization may provide a signature of individual metabolic status, which could be looked for in the fossil record and in modern environmental samples.

View Article: PubMed Central - PubMed

Affiliation: Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d'Histoire Naturelle, Université Pierre et Marie Curie - Sorbonne Universités, CNRS UMR 7590, IRD 206 Paris, France.

ABSTRACT
Microbial biomineralization sometimes leads to periplasmic encrustation, which is predicted to enhance microorganism preservation in the fossil record. Mineral precipitation within the periplasm is, however, thought to induce death, as a result of permeability loss preventing nutrient and waste transit across the cell wall. This hypothesis had, however, never been investigated down to the single cell level. Here, we cultured the nitrate reducing Fe(II) oxidizing bacteria Acidovorax sp. strain BoFeN1 that have been previously shown to promote the precipitation of a diversity of Fe minerals (lepidocrocite, goethite, Fe phosphate) encrusting the periplasm. We investigated the connection of Fe biomineralization with carbon assimilation at the single cell level, using a combination of electron microscopy and Nano-Secondary Ion Mass Spectrometry. Our analyses revealed strong individual heterogeneities of Fe biomineralization. Noteworthy, a small proportion of cells remaining free of any precipitate persisted even at advanced stages of biomineralization. Using pulse chase experiments with (13)C-acetate, we provide evidence of individual phenotypic heterogeneities of carbon assimilation, correlated with the level of Fe biomineralization. Whereas non- and moderately encrusted cells were able to assimilate acetate, higher levels of periplasmic encrustation prevented any carbon incorporation. Carbon assimilation only depended on the level of Fe encrustation and not on the nature of Fe minerals precipitated in the cell wall. Carbon assimilation decreased exponentially with increasing cell-associated Fe content. Persistence of a small proportion of non-mineralized and metabolically active cells might constitute a survival strategy in highly ferruginous environments. Eventually, our results suggest that periplasmic Fe biomineralization may provide a signature of individual metabolic status, which could be looked for in the fossil record and in modern environmental samples.

No MeSH data available.


Related in: MedlinePlus