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

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.

Simplicity in numbers: Implications of diversity for the community Bioturbation Potential (BPc)

The mobility of particles and solutes within aquatic sediment is substantially impacted by faunal bioturbation activities such as bioirrigation and sediment reworking. The non-quantitative community bioturbation potential (BPc) aims to estimate the potential of a given benthic community for bioturbation activities, based on the functional traits of the species within that community. We argue that in sufficiently diverse communities, the characteristics of individual species, expressed as traits scores, average each other out, and approach a universal constant. This enables to derive a simpler community bioturbation potential (BPs), which may be applied in cases when taxonomic expertise or trait data are not available. As a proof of concept, we evaluated a dataset of 84 benthos assemblages, and found a high degree of agreement of full BPc and simplified BPs.

Co-exposure to foodborne and waterborne ZnO nanoparticles in aquatic sediment environments enhances DNA damage and stress gene expression in freshwater Asian clam Corbicula fluminea

Co-exposure to foodborne and waterborne ZnO nanoparticles in aquatic sediment environments increases mortality, Zn bioaccumulation, stress genes expression, and DNA damage in freshwater Asian clam Corbicula fluminea.