Biology subjects

Scherlach, K.

Publications and source records attributed to Scherlach, K..

4 recordsLinked to original sources

bioRxiv2025

Dual-use virulence factors of the opportunistic pathogen Chromobacterium haemolyticum mediate haemolysis and colonization

Chromobacterium haemolyticum is an environmental bacterium that can cause severe and fatal opportunistic infections in humans and animals. Although C. haemolyticum is characterized by its strong {beta}-haemolytic activity, the molecular basis of this phenotype has remained elusive over the more than fifteen years since the species was first described. Here, we report the discovery of a family of cyclic lipodepsipeptides that are responsible for the potent haemolytic activity of C. haemolyticum. Comparative genomics of Chromobacterium spp. isolated from different environments revealed a completely conserved gene locus (chl) encoding a non-ribosomal peptide synthetase (NRPS). Metabolic profiling of C. haemolyticum DSM 19808 identified a suite of cyclic lipodepsipeptides as the products of the chl locus, with the three main congeners (jagaricin, chromolysin A and B) being elucidated by a combination of tandem mass spectrometry, chemical derivatization, and NMR spectroscopy. Significantly, a C. haemolyticum chl deletion mutant is devoid of haemolytic activity. Moreover, purified jagaricin, chromolysin A and B are haemolytic at low- micromolar concentrations in an erythrocyte lysis assay. Further bioassays demonstrated that the cyclic lipodepsipeptides are crucial for biofilm-forming and swarming behavior of C. haemolyticum. MALDI mass spectrometry imaging showed that primarily chromolysin A and B are involved in these processes in vitro. Our data shed light on the bioactivities of chromolysin A and B, specialized metabolites that likely contribute to both successful colonization of new niches and virulence potential of C. haemolyticum. ImportanceDespite the rising incidence of Chromobacterium haemolyticum as a serious opportunistic pathogen, there is limited information on whether the competitive traits that ensure its survival in its freshwater niche contribute to host infection. We present a case where bacterially produced specialized metabolites act as lynchpin chemical mediators that are not only responsible for the pronounced haemolytic phenotype of C. haemolyticum but are crucial for biofilm formation and swarming motility. These results exemplify a case of coincidental evolution, wherein the selective pressures encountered in a primary environmental niche drive the evolution of a trait impacting virulence. This knowledge provides a foundation for the development of antivirulence therapies against the emerging pathogen C. haemolyticum.

microbiology↗

bioRxiv2020

Food-Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS to Synthesize Bolaamphiphilic Lipopeptide Antibiotics

Mining the genome of the food-spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five non-ribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analyses and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro-{beta}-alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions we proved the involvement of a designated citrate synthase (CS), priming ketosynthases (KS III), a type II NRPS including a novel desaturase for enamide formation, and a multimodular NRPS generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

microbiology↗

bioRxiv2019

Highly parallelized microfluidic droplet cultivation and prioritization on antibiotic producers from complex natural microbial communities

To investigate the overwhelming part of the bacterial diversity still evading standard cultivation for its potential use in antibiotic synthesis, we have compiled a microscale-cultivation and screening system. We devised a strategy based on droplet-microfluidics taking advantage of the inherent miniaturization and high throughput. Single cells of natural samples were confined in 9 x 106 aqueous droplets and subjected to long-term incubation under controlled conditions. Subsequent a high-throughput screening for antimicrobial natural products was implemented, employing a whole cell reporting system using the viability of reporter strains as a probe for antimicrobial activity. Due to the described microscale cultivation a novel subset of bacterial strains was made available for the following screening for antimicrobials. We demonstrate the merits of the in-droplet cultivation by comparing the cultivation outcome in microfluidic droplets and on conventional agar plates for a bacterial community derived from soil by 16S rRNA gene amplicon sequencing. In-droplet cultivation resulted in a significantly higher bacterial diversity without the common overrepresentation of Firmicutes. Natural strains able to inhibit either a Gram-positive or a Gram-negative reporter strain were isolated from the microscale system and further cultivated. Thereby a variety of rare isolates was obtained. The natural products with antimicrobial activity were elucidated for the most promising candidate. Our method combines a new cultivation approach with a high-throughput search for antibiotic producers to increase the chances of finding new lead substances.

microbiology↗

bioRxiv2017

Bacterium-triggered remodeling of chromatin identifies BasR, a novel regulator of fungal natural product biosynthesis

The eukaryotic epigenetic machinery is targeted by bacteria to reprogram the response of eukaryotes during their interaction with microorganisms. In line, we discovered that the bacterium Streptomyces rapamycinicus triggered increased chromatin acetylation and thus activation of the silent secondary metabolism ors gene cluster leading to the production of orsellinic acid in the fungus Aspergillus nidulans. Using this model we aim at understanding molecular mechanisms of communication between bacteria and eukaryotic microorganisms based on bacteria-triggered chromatin modification. By genome-wide ChIP-seq analysis of acetylated histone H3 (H3K9ac, H3K14ac) we uncovered the unique chromatin landscape in A. nidulans upon co-cultivation with S. rapamycinicus. Genome-wide acetylation of H3K9 correlated with increased gene expression, whereas H3K14 appears to function in transcriptional initiation by providing a docking side for regulatory proteins. In total, histones belonging to six secondary metabolism gene clusters showed higher acetylation during co-cultivation including the ors, aspercryptin, cichorine, sterigmatocystin, anthrone and 2,4-dihydroxy-3-methyl-6-(2-oxopropyl)benzaldehyde gene cluster with the emericellamide cluster being the only one with reduced acetylation and expression. Differentially acetylated histones were also detected in genes involved in amino acid and nitrogen metabolism, signaling, and genes encoding transcription factors. In conjunction with LC-MS/MS and MALDI-MS imaging, molecular analyses revealed the cross-pathway control and Myb-like transcription factor BasR as regulatory nodes for transduction of the bacterial signal in the fungus. The presence of basR in other fungal species allowed forecasting the inducibility of ors-like gene clusters by S. rapamycinicus in these fungi, and thus their effective interaction with activation of otherwise silent gene clusters.

microbiology↗