1. ¹Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Research Network Chemistry Meets Microbiology, University of Vienna, Vienna, Austria
2. ²Department of Biology, University of Konstanz, Konstanz, Germany
3. ³Hydrology Group, Institute of Landscape Ecology, University of Münster, Münster, Germany
4. ⁴Joint Genome Institute, US Department of Energy, Walnut Creek, CA, USA

Correspondence: A Loy, Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, Research Network Chemistry Meets Microbiology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria. E-mail: loy@microbial-ecology.net.

Received 8 September 2015; Revised 15 February 2016; Accepted 22 February 2016
Advance online publication 25 March 2016

Abstract

Dissimilatory sulfate reduction in peatlands is sustained by a cryptic sulfur cycle and effectively competes with methanogenic degradation pathways. In a series of peat soil microcosms incubated over 50 days, we identified bacterial consortia that responded to small, periodic additions of individual fermentation products (formate, acetate, propionate, lactate or butyrate) in the presence or absence of sulfate. Under sulfate supplementation, net sulfate turnover (ST) steadily increased to 16–174 nmol cm^–3 per day and almost completely blocked methanogenesis. 16S rRNA gene and cDNA amplicon sequencing identified microorganisms whose increases in ribosome numbers strongly correlated to ST. Natively abundant (0.1% estimated genome abundance) species-level operational taxonomic units (OTUs) showed no significant response to sulfate. In contrast, low-abundance OTUs responded significantly to sulfate in incubations with propionate, lactate and butyrate. These OTUs included members of recognized sulfate-reducing taxa (Desulfosporosinus, Desulfopila, Desulfomonile, Desulfovibrio) and also members of taxa that are either yet unknown sulfate reducers or metabolic interaction partners thereof. Most responsive OTUs markedly increased their ribosome content but only weakly increased in abundance. Responsive Desulfosporosinus OTUs even maintained a constantly low population size throughout 50 days, which suggests a novel strategy of rare biosphere members to display activity. Interestingly, two OTUs of the non-sulfate-reducing genus Telmatospirillum (Alphaproteobacteria) showed strongly contrasting preferences towards sulfate in butyrate-amended microcosms, corroborating that closely related microorganisms are not necessarily ecologically coherent. We show that diverse consortia of low-abundance microorganisms can perform peat soil sulfate reduction, a process that exerts control on methane production in these climate-relevant ecosystems.

Please visit website for full article.