Impact of Fe(III) (Oxyhydr)oxides Mineralogy on Iron Solubilization and Associated Microbial Communities.

Fengfeng Zhang,Pascale Gautret,Mikael Motelica-Heino,Catherine Joulian,Jennifer Hellal,Fabienne Battaglia-Brunet

doi:10.3389/fmicb.2020.571244

Abstract

Iron-reducing bacteria (IRB) are strongly involved in Fe cycling in surface environments. Transformation of Fe and associated trace elements is strongly linked to the reactivity of various iron minerals. Mechanisms of Fe (oxyhydr)oxides bio-reduction have been mostly elucidated with pure bacterial strains belonging to Geobacter or Shewanella genera, whereas studies involving mixed IRB populations remain scarce. The present study aimed to evaluate the iron reducing rates of IRB enriched consortia originating from complex environmental samples, when grown in presence of Fe (oxyhydr)oxides of different mineralogy. The abundances of Geobacter and Shewanella were assessed in order to acquire knowledge about the abundance of these two genera in relation to the effects of mixed IRB populations on kinetic control of mineralogical Fe (oxyhydr)oxides reductive dissolution. Laboratory experiments were carried out with two freshly synthetized Fe (oxyhydr)oxides presenting contrasting specific surfaces, and two defined Fe-oxides, i.e., goethite and hematite. Three IRB consortia were enriched from environmental samples from a riverbank subjected to cyclic redox oscillations related to flooding periods (Decize, France): an unsaturated surface soil, a flooded surface soil and an aquatic sediment, with a mixture of organic compounds provided as electron donors. The consortia could all reduce iron-nitrilotriacetate acid (Fe(III)-NTA) in 1–2 days. When grown on Fe (oxyhydr)oxides, Fe solubilization rates decreased as follows: fresh Fe (oxyhydr)oxides > goethite > hematite. Based on a bacterial rrs gene fingerprinting approach (CE-SSCP), bacterial community structure in presence of Fe(III)-minerals was similar to those of the site sample communities from which they originated but differed from that of the Fe(III)-NTA enrichments. Shewanella was more abundant than Geobacter in all cultures. Its abundance was higher in presence of the most efficiently reduced Fe (oxyhydr)oxide than with other Fe(III)-minerals. Geobacter as a proportion of the total community was highest in the presence of the least easily solubilized Fe (oxyhydr)oxides. This study highlights the influence of Fe mineralogy on the abundance of Geobacter and Shewanella in relation to Fe bio-reduction kinetics in presence of a complex mixture of electron donors.

Highlights

Feoxides are ubiquitous components in several compartments of the critical zone and are present in many different mineralogical forms
Experiments performed with fresh Feoxides, goethite and hematite confirmed that the type of Fe mineral could influence Fe solubilization rates and the abundances of two Iron-Reducing Bacteria (IRB) commonly involved as pure strains in Fe-reducing experiments, i.e., Geobacter and Shewanella
The present study’s results showed that: (1) the sub-culturing of IRB enrichments from Fe(III)-NTA to pure iron oxides significantly modified the bacterial communities; (2) in our experimental conditions, bacterial diversity was not significantly different from one type of pureoxide to another; (3) the type of Fe oxide can influence the proportion of Geobacter and Shewanella

Summary

Introduction

Fe (oxyhydr)oxides are ubiquitous components in several compartments of the critical zone (e.g., soils, sediments, and aquifers) and are present in many different mineralogical forms. Reductive dissolution of Fe (oxyhydr)oxides can be driven by dissimilatory iron-reducing bacteria (DIRB), significantly contributing to biogeochemical cycling of Fe and subsequent TE mobilization (Cooper et al, 2006; Ghorbanzadeh et al, 2017; Levar et al, 2017). The rate of Fe(III) reduction will influence mobility of TE initially immobilized on or in Fe (oxyhydr)oxides through adsorption or co-precipitation. Crystallinity, specific surface area and size among other factors may influence reactivity of Fe (oxyhydr)oxides in relation to the metabolic activity and diversity of DIRB (Cutting et al, 2009; Aino et al, 2018)

Methods

Results

Discussion

Conclusion