Biology subjects

Dahl, C.

Publications and source records attributed to Dahl, C..

3 recordsLinked to original sources

bioRxiv2026

A widespread SCCmec-located gene cluster protects methicillin-resistant Staphylococcus aureus against toxic polysulfides

The genus Staphylococcus contains important human commensals and pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), which is a frequent colonizer of humans and a leading cause of healthcare-associated and life-threatening infections. While its virulence and pathogenicity have been extensively studied, factors driving the colonization and distribution of MRSA as a pathobiont are less understood. Here, we report on a cst sulfide detoxification gene cluster located on SCCmec, the antibiotic resistance-mediating genetic element of MRSA. Bioinformatic analyses revealed a heterogeneous distribution of cst clusters in staphylococcal genomes and that many clinically relevant SCCmec types introduce an additional cst cluster (cst2) to MRSA. While the canonical cst cluster (cst1) consists of the five genes tauE, cstR, cstA, cstB, and sqr, most staphylococcal cst clusters, including the SCCmec-located cst2, lack the sqr gene, which encodes for a sulfide:quinone reductase responsible for the initial step of sulfide detoxification. Growth experiments with a diverse set of representative Staphylococcus strains, cst-deletion mutants, and complementation with cst-containing plasmids demonstrated that the cst cluster enables sqr-independent polysulfide-detoxification. Furthermore, the additional cst2 cluster confers high polysulfide tolerance to MRSA, providing the pathogen with a unique advantage in polysulfide-rich environments. Using serial passaging co-cultivation experiments with methicillin-sensitive S. aureus (MSSA) strains, we demonstrated that in the presence of polysulfides cst2-containing MRSA can invade an established MSSA population and outperform the occupying resident in direct competition. Overall, our findings indicate that polysulfides are critical stress factors for staphylococci, potentially contributing to the spread of cst2-containing SCCmec and MRSA. ImportanceMethicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent human pathogens responsible for millions of life-threatening infections worldwide. It acquires antibiotic resistance through the genetic element SCCmec, which contains the characteristic mecA gene that renders the organism resistant to most classes of {beta}-lactam antibiotics. Besides mecA and accessory gene complexes necessary for the transfer of SCCmec and phenotype manifestation, the genetic element also contains prominent gene clusters with unknown functions. Here, we report on a (poly-)sulfide-detoxification gene cluster (cst2) present on SCCmec that provides MRSA with a unique advantage in environments containing polysulfides - highly reactive intermediates of sulfide oxidation naturally occurring as microbial stressors on mucosal surfaces inside the human body. We demonstrate that in the presence of polysulfides, cst2 enables MRSA to outperform non-MRSA in direct competition, thus supporting the invasion and proliferation of this pathogen independent of its antibiotic resistance.

microbiology↗

bioRxiv2025

In Hyphomicrobium denitrificans two related sulfane-sulfur responsive transcriptional repressors regulate thiosulfate oxidation and have a deep impact on nitrate respiration and anaerobic biosyntheses

Bacteria have evolved multiple strategies to sense and respond to the availability of inorganic reduced sulfur compounds such as thiosulfate. In Hyphomicrobium denitrificans, an obligately chemoorganoheterotrophic Alphaproteobacterium, the use of thiosulfate as a supplemental electron donor is regulated by two homologous sulfane-sulfur-responsive ArsR-type transcriptional repressors, sHdrR and SoxR. Here, we provide information on the distribution and phylogeny of sHdrR, the relevance of its two conserved cysteines in vivo, and identify the genes controlled by SoxR and sHdrR not only by targeted qRT-PCR but also by global RNA-Seq-based analyses of regulator-deficient mutant strains.The absence of sHdrR and SoxR affected 165 and 170 genes, respectively, with 138 genes overlapping. SoxR affects the sox genes for periplasmic thiosulfate oxidation and sulfane sulfur import into the cytoplasm, as well as the lip-shdr-lbpA genes encoding the cytoplasmic enzymes essential for sulfite formation. sHdrR affects only a subset of these genes. The transcription of sox genes remains unaltered in its absence. sHdrR and SoxR act cooperatively, possibly involving heterodimer formation, and their activity also involves interaction with other transcriptional regulators. Most importantly, sHdrR/SoxR regulation extends far beyond sulfur oxidation and deeply affects anaerobic metabolism, particularly denitrification in H. denitrificans.

microbiology↗

bioRxiv2023

A cascade of sulfur transferases delivers sulfur to the sulfur-oxidizing heterodisulfide reductase-like complex

A heterodisulfide reductase-like complex (sHdr) and novel lipoate-binding proteins (LbpAs) are central players of a wide-spread pathway of dissimilatory sulfur oxidation. Bioinformatic analysis demonstrate that the cytoplasmic sHdr-LbpA systems are always accompanied by sets of sulfur transferases (DsrE proteins, TusA, rhodaneses). The exact composition of these sets may vary depending on the organism and sHdr system type. To enable generalizations, we studied model sulfur oxidizers from distant bacterial phyla, i.e. Aquificota and Pseudomonadota. DsrE3C of the chemoorganotrophic Alphaproteobacterium Hyphomicrobium denitrificans and DsrE3B from the Gammaproteobacteria Thioalkalivibrio sp. K90mix, an obligate chemolithotroph, and Thiorhodospira sibirica, an obligate photolithotroph, are homotrimers that donate sulfur to TusA. Additionally, the hyphomicrobial rhodanese-like protein Rhd442 exchanges sulfur with both TusA and DsrE3C. The latter is essential for sulfur oxidation in Hm. denitrificans. TusA from Aquifex aeolicus (AqTusA) interacts physiologically with AqDsrE, AqLbpA and AqsHdr proteins. This is particularly significant as it establishes a direct link between sulfur transferases and the sHdr-LbpA complex that oxidizes sulfane sulfur to sulfite. In vivo, it is unlikely that there is a strict unidirectional transfer between the sulfur-binding enzymes studied. Rather, the sulfur transferases form a network, each with a pool of bound sulfur. Sulfur flux can then be shifted in one direction or the other depending on metabolic requirements. A single pair of sulfur-binding proteins with a preferred transfer direction, such as a DsrE3-type protein towards TusA, may be sufficient to push sulfur into the sink where it is further metabolized or needed. SIGNIFICANCE STATEMENTA network of bacterial sulfur transferases is uncovered and characterized that ultimately delivers sulfur to a complex cytoplasmic sulfur-oxidizing metalloenzyme, sHdr, that resembles heterodisulfide reductase from methanogenic archaea and interacts with lipoate-binding proteins. Similar sets of sulfur transferases occur in phylogenetically distant bacteria, underscoring the fundamental importance of the work.

biochemistry↗