Microbial sulfur metabolism

Genetics and biochemistry of sulfur oxidation

The conversion of sulfur compounds is one of the oldest biological strategies for energy conservation, and even today sulfur-metabolizing prokaryotes are of immense importance to the biogeochemical sulfur cycle. This global cycle has implications for human health, climate change, and bioremediation. Our focus is on the study of oxidative sulfur metabolism in bacteria, with emphasis on the biochemical, biophysical, and structural characterization of the enzymes involved.

Metalloenzymes and sulfur transferases

Many enzymes of oxidative sulfur metabolism in prokaryotes are metalloproteins whose processing requires special techniques such as the complete exclusion of oxygen (Dahl 2020). In the purification of the enzyme complexes from the original organisms, e.g. Thioalkalivibrio thiocyanoxydans, a variety of column chromatographic methods are used. In some cases, production in Escherichia coli is also possible. (Ernst et al. 2020). In the bacterial cytoplasm, reduced sulfur is handled in bound form and transferred to its target proteins via sulfur transferases. These proteins are also the subject of our research. In addition, we develop methods for gene manipulation for model organisms such as Hyphomicrobium denitrificans and Allochromatium vinosum and pursue systems biology approaches (genomics, transcriptomics, proteomics und metabolomics) (Koch et al. 2018).

© Volker Lannert
© Christiane Dahl

Assembly of lipoic acid

Lipoic acid is an essential biomolecule found in all domains of life and is involved not only in central carbon metabolism but also in dissimilatory sulfur oxidation (Cao et al. 2018). The mechanisms for lipoate assembly in mitochondria and chloroplasts of higher eukaryotes are prokaryotic in origin. We have found a novel pathway for lipoate assembly in bacteria based on an sLpl(AB) lipoate:protein ligase that binds octanoate or lipoate to Apo proteins and on highly oxygen-sensitive iron-sulfur proteins, LipS1 and LipS2, which together act as a lipoyl synthase and insert two sulfur atoms. We aim to characterize these enzymes and their interactions by analyzing their substrate spectrum in detail. We also aim to clarify the occurrence and general significance of the new lipoylation pathway in bacteria and finally to elucidate the origin and evolution of the different lipoyl synthesis machineries.

Regulation of sulfur metabolism

Many bacteria use reduced sulfur compounds instead of or in addition to organic compounds. In these cases, regulation of sulfur oxidation is required to adapt metabolic flux to environmental conditions. This regulation occurs at the level of transcription, but little is known about the signal transduction and the DNA-binding regulatory proteins involved. Our model organism Hyphomicrobium denitrificans has two related homodimeric repressor proteins, SoxR and sHdrR, which closely interact to regulate the expression of sox genes for a periplasmic multienzyme system for thiosulfate oxidation and shr-lbpA genes for a cytoplasmic metalloenzyme complex that oxidizes sulfane sulfur to sulfite (Li et al. 2023). We want to elucidate in detail the mechanisms underlying this regulation.

© Volker Lannert
© Sebastian Tanabe


The inorganic and organic compounds involved in the sulfur cycle not only represent a huge sulfur reservoir, but are also used by prokaryotes as energy and/or carbon sources. The underlying biochemistry is very complex, and the corresponding metabolic pathways are often not conserved and may vary even within strains of the same species. This complicates ecological and evolutionary studies based on rapid analysis of large (meta-)genomic datasets that aim to elucidate, among other things, the metabolic capacity of microbial communities. To facilitate these analyses, we are developing a comprehensive equivalent Hidden Markov Model (HMM)-based tool for rapid annotation and synteny analysis of proteins in prokaryotic genomes involved in the sulfur cycle (Tanabe et al. 2022, 2023). Our open-source analysis tools and software are available via Github.  The calculation of phylogenetic trees is also part of our portfolio.


Here you can find a list of our previously published papers.


Here you can find a list of the current members of the research group.

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