Enriching Acidophilic Fe(II)-oxidizing Bacteria in No-flow, Fed-batch Systems

Abstract

Low-pH microbial Fe(II) oxidation occurs naturally in some Fe(II)-rich acid mine drainage (AMD) ecosystems across so-called terraced iron formations. Indigenous acidophilic Fe(II)-oxidizing bacterial communities can be incorporated into both passive and active treatments to remove Fe from the AMD solution. Here, we present a protocol of enriching acidophilic Fe(II)-oxidizing bacteria in no-flow, fed-batch systems. Mixed cultures of naturally occurring microbes are enriched from the fresh surface sediments at AMD sites using a chemo-static bioreactor (Eppendorf BioFlo®/Celligen® 115 Fermentor) with respect to constant stirring speed, temperature, pH and unlimited dissolved oxygen. Ferrous sulfate is discontinuously added to the reactor as the primary substrate to enrich for acidophilic Fe(II)-oxidizing bacteria. Successfully and efficiently enriching acidophilic Fe(II)-oxidizing bacteria helps to exploit this biogeochemical process into AMD treatment systems.