Distinctive Microbial Community Associated with Pond Sediment Magnetite Grains

Abstract

Magnetite is a naturally occurring ferrimagnetic mineral. It can be formed by both abiotic and biotic processes. Biological magnetite formation through dissimilatory iron reduction has been well-studied in culture since those bacterial species that perform dissimilatory iron reduction have various applications. However, from an ecological perspective, their presence and role as a magnetite former in natural environments are unclear. In this study, bacteria associated with magnetite grains from freshwater pond sediment were investigated. Pond sediment samples were collected and subjected to magnetic separation, enriching magnetite grains while leaving magnetite-depleted fraction behind. Soil DNA was taken from each of the magnetite-enriched and magnetite-depleted samples, and the V3 region of bacterial 16S ribosomal RNA (rRNA) gene was amplified. Using next generation sequencing (NGS) technique, bacterial community structure of the magnetite-enriched fraction was compared to that of the magnetite-depleted fraction. In the magnetite-enriched fraction, the most abundant operational taxonomic unit (OTU) belonged to Geobacter, a genus known to include several species that can form magnetite in culture condition. There were several other bacterial species particularly abundant in the magnetite-enriched fraction, inviting further investigation of their potential contribution to magnetite formation in nature. Overall, bacterial community structure of the magnetite-enriched and magnetite-depleted fractions was distinct from each other, providing a glimpse towards understanding how bacterial diversities in sediments and soils are structured and how a variety of bacterial species can coexist in soils.