3 Geochemistry: Advances in Low-Temperature and Isotope Geochemistry

Sunday, 4 November 2012
8:00 AM - 12:00 PM
209AB

SUSPENDED FLOC: MICROBIAL IRON REDOX CYCLING, FE BIOMINERALS AND TRACE ELEMENT BEHAVIOUR

Paper number: 3-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

Current perceptions regarding the highly environmentally restricted occurrence of Fe metabolizing microorganisms has directed investigation and thus driven our understanding of the global cycling of Fe; a key biogeochemical element. However, our discovery of pelagic, floc-associated multi-species, Fe(III)-reducing and Fe(II)-oxidizing bacterial consortia across diverse oxygenated aquatic systems is a game-changer in geomicrobial ecology. We isolated these consortia from conditions not predicted to sustain microbial Fe metabolism and therefore not investigated in environmental studies of microbial Fe redox cycling. Our findings challenge the current paradigm that Fe redox cycling bacteria are restricted to specific niche geochemical environments and identify that ecological collaborations between aero-intolerant Fe-bacteria with aerobic microorganisms provides a strategy to enable redox cycling of Fe at the microscale under much broader O2 and pH ranges than previously thought, with implications for Fe biominerals and associated trace element behaviour.

Across these widely varying aquatic systems, floc trace element (TE: Ag, As, Cu, Ni and Co) abundance and partitioning was dominated by the amorphous Fe oyhxydroxide fraction, concentrating TE up to ~55x above that of surficial bed sediments. Further, Fe biomineralization associated with Fe metabolising bacteria indicates the strong linkages between microbial metabolism and Fe mineral phases and TE sequestration in floc. While floc FeOOH is the dominant floc TE sequestration phase, EPS and microbial constituents underpin floc FeOOH occurrence, ultimately creating a distinctly different solid than bed sediments with differing controls on TE uptake. Enrichment of iron reducing and oxidizing microorganisms from floc across these highly varying systems indicate previously unconstrained Fe cycling occurs at the floc scale that is controlled by floc ecology, not by system geochemistry.