Biology subjects

Lemon, D. J.

Publications and source records attributed to Lemon, D. J..

4 recordsLinked to original sources

bioRxiv2023

Integrin-like adhesin CglD confers traction and stabilizes bacterial focal adhesions involved in myxobacterial gliding motility

AO_SCPLOWBSTRACTC_SCPLOWIntegrins are crucial for eukaryotic cell attachment and motility within the extracellular matrix (ECM) via focal-adhesion formation, with their evolutionary emergence important for the development of multicellularity. Intriguingly, single gliding cells of the predatory deltaproteobacterium Myxococcus xanthus form bacterial focal-adhesion (bFA) sites; therein, helically-trafficked motors become immobilized at anchored locations through Glt apparatus association with cell-surface integrin I-domain-like adhesin CglB. Using traction-force, bead-force, and total internal reflection-fluorescence microscopies combined with biochemical approaches, we herein identify the von Willebrand A domain-containing cell-surface lipoprotein CglD to be a {beta}-integrin-like outer-membrane lipoprotein that functionally associates with and anchors the trans-envelope Glt-CglB gliding apparatus, stabilizing and efficiently anchoring this assembly at bFAs. Calcium dependence governs CglD importance, consistent with its integrated ECM eukaryotic cartilage oligomeric matrix protein domains. CglD thus confers mechanosensory and mechanotransductory capabilities to the gliding apparatus, helping explain bFA-mediated trans-envelope force transduction, from inner-membrane-embedded motors to the cell surface.

microbiology↗

bioRxiv2021

Unraveling a Bacterial Starvation Response Through the Direct Targets of a Starvation-Induced Transcriptional Activator

Organisms frequently encounter environments with nutrient shortages and their survival depends on changes in physiology and the ability to conserve resources. In bacteria, many physiological changes associated with starvation have been identified, but the underlying genetic components and regulatory networks that direct these physiological changes are often poorly defined. Here, we aimed to better define the gene regulatory networks that mediate the starvation response in Myxococcus xanthus, a bacterium that copes with starvation by producing fruiting bodies filled with dormant and stress-resistant spores. We focused on the direct promoter/gene targets of Nla28, a transcriptional activator/enhancer binding protein (EBP) that is important for early rounds of gene expression following starvation. Using expression profiling to identify genes that are downregulated in nla28 mutant cells and bioinformatics to identify the putative promoters of these genes, 12 potential promoter targets (37 genes) of Nla28 were identified. The results of in vitro promoter binding assays, coupled with in vitro and in vivo mutational analyses, suggested that the 12 promoters are in vivo targets of Nla28 and that Nla28 dimers use tandem, imperfect repeats of an 8-bp sequence for binding. Interestingly, nine of the Nla28 target promoters are intragenic, located in the protein coding sequence of an upstream gene or in the protein coding sequence of one gene within an operon (internal promoters). Based on mutational analyses, we concluded that the 12 Nla28 target loci contain at least one gene important for production of stress-resistant spores following starvation. Most of these loci contain genes predicted to be involved in regulatory or defense-related functions. Using the consensus Nla28 binding sequence, followed by bioinformatics and expression profiling, 58 additional promoters and 102 genes were tagged as potential Nla28 targets. Among these putative Nla28 targets, functions such as regulatory, metabolic and cell envelope biogenesis were commonly assigned to genes.

microbiology↗

bioRxiv2020

Bacterial glycocalyx integrity drives multicellular swarm biofilm dynamism

Bacterial surface exopolysaccharide (EPS) layers are key determinants of biofilm establishment and maintenance, leading to the formation of higher-order 3D structures conferring numerous survival benefits to a cell community. In addition to a specific EPS glycocalyx, we recently revealed that the social {delta}-proteobacterium Myxococcus xanthus secretes a novel biosurfactant polysaccharide (BPS), with both EPS and BPS polymers required for type IV pilus (T4P)-dependent swarm expansion via spatio-specific biofilm expression profiles. Thus the synergy between EPS and BPS secretion somehow modulates the multicellular lifecycle of M. xanthus. Herein, we demonstrate that BPS secretion functionally-activates the EPS glycocalyx via its destabilization, fundamentally altering the characteristics of the cell surface. This impacts motility behaviours at the single-cell level as well as the aggregative capacity of cells in groups via EPS fibril formation and T4P assembly. These changes modulate structuration of swarm biofilms via cell layering, likely contributing to the formation of internal swarm polysaccharide architecture. Together, these data reveal the manner by which the interplay between two secreted polymers induces single-cell changes that modulate swarm biofilm communities.

microbiology↗

bioRxiv2020

CglB adhesins secreted at bacterial focal adhesions mediate gliding motility

AO_SCPLOWBSTRACTC_SCPLOWThe predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal adhesion (bFA) sites to power gliding motility. Using TIRF and force microscopy, we herein identify the integrin I-domain-like outer-membrane (OM) lipoprotein CglB as an essential substratum-coupling protein of the gliding motility complex. Similar to most known OM lipoproteins, CglB is anchored on the periplasmic side of the OM and thus a mechanism must exist to secrete it to the cell surface in order for it to interact with the underlying substratum. We reveal this process to be mediated by a predicted OM {beta}-barrel structure of the gliding complex. This OM platform was found to regulate the conformational activation and secretion of CglB across the OM. These data suggest that the gliding complex promotes surface exposure of CglB at bFAs, thus explaining the manner by which forces exerted by inner-membrane motors are transduced across the cell envelope to the substratum; they also uncover a novel protein secretion mechanism, highlighting the ubiquitous connection between secretion and bacterial motility.

microbiology↗