Diversity, ecophysiology, and evolution of sulfate-reducing microbes
Bacterial and archaeal lineages known to contain SRM. | Sulfate-reducing microbes (SRM) are ubiquitous, inhabiting mainly anoxic zones but also the oxic/anoxic interface in various natural and man-made environments. The unifying physiological trait of these microorganisms is their ability to use sulfate as terminal electron acceptor coupled with the generation of energy. This unique geobiological process is called dissimilatory sulfate reduction or anaerobic sulfate respiration |
| and is exclusively restricted to the archaeal and bacterial domains of life, making SRM essential biotic component of global sulfur cycling. Dissimilatory sulfate reduction is a very ancient process. Molecular and geological data indicate that some of first life forms on the early earth probably already employed this type of physiology. From the viewpoint of modern rRNA-based taxonomy SRM form a rather heterogenous group. All so far described sulfate-reducing species belong either to one of the five major bacterial lineages Proteobacteria, Firmicutes, Nitrospirae, Thermodesulfobacteria, or Thermodesulfobiaceae or to the two archaeal phyla Euryarchaeota and Crenarcheota. Although SRM are most abundant in environments with high sulfate concentrations such as marine sediments, their versatile metabolism endows them with manifold opportunities to also make a living under sulfate-poor conditions. While of great importance for the functioning of many ecosystems, SRM can also pose a potential threat to human economy or health. Oil production is only one example where the activity of SRM is detrimental, causing oil souring and corrosion of pipelines. |
Project: Unknown SRM in acidic, sulfate-poor wetlands
Hidden SRM in an acidic fen | Environmental inventories of dsrAB, genes that encode major subunits of the dissimilatory (bi)sulfite reductase and are diagnostic for SRM, have recently demonstrated that the diversity of this guild is far greater than previously recognized by cultivation-based surveys. For example, we could show that the SRP community in an acidic fen soil system is largely represented by novel dsrAB sequence types which form novel, deep-branching lineages in the phylogenetic tree and thus most likely derive from yet unknown SRM. Similar dsrAB sequences were also found in other wetland ecosystems, indicating a widespread distribution of these novel SRM lineages in the environment. |
| However, apart from their molecular signature nothing is currently known about these previously hidden SRM. We aim to considerably extend our current knowledge of these presumably important microorganisms, which have so far resisted cultivation, by using the acidic fens as a model system. Based on already available sequence data, novel cultivation-independent methods such as DNA microarrays and stable isotope probing will be developed and applied for monitoring changes in the diversity and cellular activity of SRM thriving in the acidic fen system, and for yielding insights into their metabolic properties. A further goal is the selective enrichment, which is also a requirement for future (meta)genomic studies, and subsequent taxonomic identification of the novel SRM. The combined application of these complementary techniques should allow one to unravel important features of the biology of these novel SRM, for which currently nothing more than partial sequences of a key enzyme are known. |
Project: Thermophilic, sporeforming SRM in cold and temperate marine sediments
Marine sediment from a
Svalbard fjord. | Sulfate-reducing microbes (SRM) are of global relevance for sulfur cycling and the mineralization of carbon in the upper, anoxic sediment layers of the seafloor. In addition to the common psychro- and/or mesophilic microbial SRM populations, some cold and temperate marine sediments unexpectedly host a cryptic community of presumably inactive spores from thermophilic SRM, whose source and mode of dispersal are currently unknown. One hypothesis is that these heat-loving, sporeforming SRM grow in the hot subsurface and are transported to the surface as spores via locally defined seepages, which could be areas where also deep gas and possibly oil occasionally penetrate up to the sediment surface. The apparent inability of the thermophilic SRM to grow in the cold sediments where they were discovered provides a unique possibility to exemplarily study the biogeography and dispersal of microbial cells in the oceans. We thus aim to shed light on the origin of thermophilic SRM spores by revealing their diversity and distribution in ocean sediments and waters of various |
| geographic regions using a combination of molecular, biogeochemical, and cultivation-based methods. Practical molecular and biogeochemical assays will be developed for the detection and quantification of thermophilic, sporeforming SRM and applied to test if these organisms are bioindicators for fluid flow from the hot subsurface and thus potentially also for deep oil/gas deposits. |
This research is supported by: 
Link
 PhyloChips
Investigated by: Alexander Loy, Michael Pester, Bela Hausmann, Martina Putz
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