Secondary Mineral Formation During Ferrihydrite Reduction by <i>Shewanella oneidensis</i> MR-1 Depends on Incubation Vessel Orientation and Resulting Gradients of Cells, Fe²⁺ and Fe Minerals

<div><p>In previous studies on microbial ferric iron (Fe(III)) reduction varying results regarding reduction rates and secondary mineral formation have been reported for almost identical conditions regarding temperature, pH, medium composition, Fe(III) mineral identity and bulk iron concentration. Here we show that in addition to physico-chemical parameters also geometric aspects, i.e., incubation orientation and dimension of cultivation vessels, influence the reduction rates and mineralogy. We incubated the Fe(III)-reducer <i>Shewanella oneidensis</i> MR-1 in test tubes at ferrihydrite (FH) concentrations of 1.3–50 mM either in vertical or horizontal orientation. Cells and minerals formed a pellet at the bottom of the tubes with different thicknesses at the same initial FH concentration depending on the incubation orientation. In vertically incubated tubes thick FH pellets were present at the bottom of the tubes and magnetite was formed in all setups with ≥2.5 mM initial FH. In tubes that were incubated horizontally no magnetite was formed in presence of <5 mM initial FH. Spatially resolved analysis of the supernatant and mineral sediment including voltammetric microelectrodes, Xray diffraction and Mössbauer spectroscopy revealed strong gradients of Fe²⁺ in both the aqueous supernatant and mineral pellets, whereas a heterogeneous distribution of cells and minerals in the sediment pellet was detected. The highest cell density and, consequently, the initiation of FH reduction was found at the mineral-supernatant interface. This study demonstrates that small changes in incubation conditions can significantly influence and even change the experimental results of geomicrobiological experiments.</p></div

Independent predictors of inflammation and atherosclerosis.

<p>Independent predictors of inflammation and atherosclerosis.</p

Relationships between parameters for autonomic function, inflammatory markers, atherosclerosis and clinical factors.

<p>Relationships between parameters for autonomic function, inflammatory markers, atherosclerosis and clinical factors.</p

Characteristics of study population and comparison between subjects with or without prevalent CVD.

<p>Characteristics of study population and comparison between subjects with or without prevalent CVD.</p

Forest plots of the HR of the combined endpoint per one SD of average mean CCA-IMT (with 95% CIs).

<p>Panel I: Group A (asymptomatic individuals with three or more CVD risk factors), HR adjusted for age, sex and annual mean CCA-IMT change (model 1). Panel II: Group A (asymptomatic individuals with three or more CVD risk factors), HR adjusted for age, sex, annual mean CCA-IMT change and other CVD risk factors (model 2). Panel III: Group B (asymptomatic individuals with carotid plaques), HR adjusted for age, sex and annual mean CCA-IMT change (model 1). Panel IV: Group B (asymptomatic individuals with carotid plaques), HR adjusted for age, sex, annual mean CCA-IMT change and other CVD risk factors (model 2). Panel V: Group C (individuals with previous CVD events), HR adjusted for age, sex and annual mean CCA-IMT change (model 1). Panel VI: Group C (individuals with previous CVD events), HR adjusted for age, sex, annual mean CCA-IMT change and other CVD risk factors (model 2).</p

Meta-regression plot for the HR (combined endpoint) per SD of annual mean CCA-IMT change (model 1), by the correlation of baseline and follow-up common CIMT.

<p>The size of each circle represents the precision of the log HR.</p

Cohorts and subsamples.

<p>Cohorts and subsamples.</p

Forest plots of the HR of the combined endpoint per one SD of annual mean CCA-IMT change (with 95% CIs).

<p>Panel I: Group A (asymptomatic individuals with three or more CVD risk factors), HR adjusted for age, sex and average mean CCA-IMT (model 1). Panel II: Group A (asymptomatic individuals with three or more CVD risk factors), HR adjusted for age, sex, average mean CCA-IMT and other CVD risk factors (model 2). Panel III: Group B (asymptomatic individuals with carotid plaques), HR adjusted for age, sex and average mean CCA-IMT (model 1). Panel IV: Group B (asymptomatic individuals with carotid plaques), HR adjusted for age, sex, average mean CCA-IMT and other CVD risk factors (model 2). Panel V: Group C (individuals with previous CVD events), HR adjusted for age, sex and average mean CCA-IMT (model 1). Panel VI: Group C (individuals with previous CVD events), HR adjusted for age, sex, average mean CCA-IMT and other CVD risk factors (model 2).</p

Inclusion criteria.

<p>Inclusion criteria.</p