Journal Article
Applied and Environmental Microbiology, vol. 80, iss. 9, pp. 2665-2671, 2014
Authors
Ryan M. Jennings, Laura M. Whitmore, James J. Moran, Helen W. Kreuzer, William P. Inskeep, R. M. Kelly
Abstract
ABSTRACT
The fixation of inorganic carbon has been documented in all three domains of life and results in the biosynthesis of diverse organic compounds that support heterotrophic organisms. The primary aim of this study was to assess carbon dioxide fixation in high-temperature Fe(III)-oxide mat communities and in pure cultures of a dominant Fe(II)-oxidizing organism (
Metallosphaera yellowstonensis
strain MK1) originally isolated from these environments. Protein-encoding genes of the complete 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) carbon dioxide fixation pathway were identified in
M. yellowstonensis
strain MK1. Highly similar
M. yellowstonensis
genes for this pathway were identified in metagenomes of replicate Fe(III)-oxide mats, as were genes for the reductive tricarboxylic acid cycle from
Hydrogenobaculum
spp. (
Aquificales
). Stable-isotope (
13
CO
2
) labeling demonstrated CO
2
fixation by
M. yellowstonensis
strain MK1 and in
ex situ
assays containing live Fe(III)-oxide microbial mats. The results showed that strain MK1 fixes CO
2
with a fractionation factor of ∼2.5‰. Analysis of the
13
C composition of dissolved inorganic C (DIC), dissolved organic C (DOC), landscape C, and microbial mat C showed that mat C is from both DIC and non-DIC sources. An isotopic mixing model showed that biomass C contains a minimum of 42% C of DIC origin, depending on the fraction of landscape C that is present. The significance of DIC as a major carbon source for Fe(III)-oxide mat communities provides a foundation for examining microbial interactions that are dependent on the activity of autotrophic organisms (i.e.,
Hydrogenobaculum
and
Metallosphaera
spp.) in simplified natural communities.
