Biology subjects

Sallmen, J. W.

Publications and source records attributed to Sallmen, J. W..

4 recordsLinked to original sources

bioRxiv2024

Discovery of lydiamycin A biosynthetic gene cluster in the plant pathogen Rhodococcus fascians guides structural revision and identification of molecular target

The natural products actinonin and matlystatin feature an N-hydroxy-2-pentyl-succinamyl (HPS) chemophore that facilitates metal chelation and confers their metalloproteinase inhibitory activity. Actinonin is the most potent natural inhibitor of peptide deformylase (PDF) and exerts antimicrobial and herbicidal bioactivity by disrupting protein synthesis. Here, we used a genomics-led approach to identify candidate biosynthetic gene clusters (BGCs) hypothesised to produce novel HPS-containing natural products. We show that one of these BGCs is on the pathogenicity megaplasmid of the plant pathogen Rhodococcus fascians and produces lydiamycin A, a macrocyclic pentapeptide. The presence of genes predicted to make a HPS-like chemophore informed the structural recharacterisation of lydiamycin via NMR and crystallography to show it features a rare 2-pentyl-succinyl chemophore. We demonstrate that lydiamycin A inhibits bacterial PDF in vitro and show that a cluster-situated PDF gene confers resistance to lydiamycin A, representing a novel self-immunity mechanism associated with the production of a PDF inhibitor. In planta competition assays showed that lydiamycin enhances the fitness of R. fascians during plant colonisation. This study highlights how a BGC can inform the structure, biochemical target and ecological function of a natural product.

microbiology↗

bioRxiv2024

Firing of Streptomyces coelicolor contractile injection system requires the membrane protein CisA

Bacterial contractile injection systems (CIS) are phage tail-like macromolecular complexes that mediate cell-cell interactions by injecting effector proteins into target cells. CIS from Streptomyces coelicolor (CISSc) are localized in the cytoplasm. Under stress, they induce cell death and impact the Streptomyces life cycle. It remains unknown, however, whether CISSc require accessory proteins to directly interact with the cytoplasmic membrane to function. Here, we characterize the putative membrane adaptor CisA, a conserved factor in CIS gene clusters across Streptomyces species. We show by cryo-electron tomography imaging and in vivo assays that CISSc contraction and function depend on CisA. Using single-particle cryo-electron microscopy, we provide an atomic model of the extended CISSc apparatus; however, CisA is not part of the complex. Instead, our findings show that CisA is a membrane protein with a cytoplasmic N-terminus predicted to interact with CISSc components, thereby providing a possible mechanism for mediating CISSc recruitment to the membrane and subsequent firing. Our work shows that CIS function in multicellular bacteria is distinct from Type 6 Secretion Systems and extracellular CIS, and possibly evolved due to the role CISSc play in regulated cell death.

microbiology↗

bioRxiv2022

Cytoplasmic contractile injection systems mediate cell death in Streptomyces

Contractile injection systems (CISs) are bacteriophage tail-like structures that mediate bacterial cell-cell interactions. While CISs are highly abundant across diverse bacterial phyla, representative gene clusters in Gram-positive organisms remain poorly studied. Here we characterize a CIS in the Gram-positive multicellular model organism Streptomyces coelicolor and show, that in contrast to most other CISs, S. coelicolor CIS (CISSc) mediate cell death in response to stress and impact cellular development. CISSc are expressed in the cytoplasm of vegetative hyphae and not released into the medium. Our cryo-electron microscopy structure enabled the engineering of non-contractile and fluorescently tagged CISSc assemblies. Cryo-electron tomography showed that CISSc contraction is linked to reduced cellular integrity. Fluorescence light microscopy furthermore revealed that CISSc contraction mediates cell death upon encountering different types of stress. Finally, the absence of functional CISSc had an impact on hyphal differentiation and secondary metabolite production. Our results provide new functional insights into CISs in Gram-positive organisms and a framework for studying novel intracellular roles, including regulated cell death and life cycle progression in multicellular bacteria.

microbiology↗

bioRxiv2020

A conserved cell division protein directly regulates FtsZ dynamics in filamentous and unicellular actinobacteria

Bacterial cell division is driven by the polymerization of the GTPase FtsZ into a contractile structure, the so-called Z-ring. This essential process involves proteins that modulate FtsZ dynamics and hence the overall Z-ring architecture. Actinobacteria, like Streptomyces and Mycobacterium lack known key FtsZ-regulators. Here we report the identification of SepH, a conserved actinobacterial protein that directly regulates FtsZ dynamics. We show that SepH is crucially involved in cell division in Streptomyces and that it binds FtsZ via a conserved helix-turn-helix motif, stimulating the assembly of FtsZ protofilaments. Comparative in vitro studies using the SepH homolog from Mycobacterium further reveal that SepH can also bundle FtsZ protofilaments, indicating an additional Z-ring stabilizing function in vivo. We propose that SepH plays a crucial role at the onset of cytokinesis in actinobacteria by promoting the rapid assembly of FtsZ filaments into division-competent Z-rings that can go on to mediate septum synthesis.

microbiology↗