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Predation by Myxococcus xanthus Induces Bacillus subtilis to Form Spore-Filled Megastructures.
Appl Environ Microbiol. 2014 Oct 17;
Authors: Müller S, Strack SN, Ryan SE, Kearns DB, Kirby JR
Biofilm formation is a common mechanism for surviving environmental stress and can be triggered by both intraspecies and interspecies interactions. Prolonged predator-prey interactions between the soil bacteria Myxococcus xanthus and Bacillus subtilis was found to induce the formation of a new type of B. subtilis biofilm, termed megastructures. Megastructures are tree-like brachiations, as much as 500 microns in diameter and raised above the surface between 150 to 200 microns and are filled with viable endospores embedded within a dense matrix. Megastructure formation did not depend on TasA, EspE, SinI, RemA or surfactin production and thus is genetically distinguishable from colony biofilm formation on MSgg medium. As B. subtilis endospores are not susceptible to predation by M. xanthus, megastructures appear to provide an alternative mechanism for survival. In addition, M. xanthus fruiting bodies were found in nearly all instances immediately adjacent to the megastructures, suggesting that M. xanthus is unable to acquire sufficient nutrients from cells housed within the megastructures. Lastly, a B. subtilis mutant lacking the ability to defend itself via bacillaene production, formed megastructures more rapidly than the parent. Together, the results indicate that production of the megastructure facilitates B. subtilis escape into dormancy via sporulation.
PMID: 25326308 [PubMed - as supplied by publisher]
Bacillaene and sporulation protect Bacillus subtilis from predation by Myxococcus xanthus.
Appl Environ Microbiol. 2014 Sep;80(18):5603-10
Authors: Müller S, Strack SN, Hoefler BC, Straight PD, Kearns DB, Kirby JR
Myxococcus xanthus and Bacillus subtilis are common soil-dwelling bacteria that produce a wide range of secondary metabolites and sporulate under nutrient-limiting conditions. Both organisms affect the composition and dynamics of microbial communities in the soil. However, M. xanthus is known to be a predator, while B. subtilis is not. A screen of various prey led to the finding that M. xanthus is capable of consuming laboratory strains of B. subtilis, while the ancestral strain, NCIB3610, was resistant to predation. Based in part on recent characterization of several strains of B. subtilis, we were able to determine that the pks gene cluster, which is required for production of bacillaene, is the major factor allowing B. subtilis NCIB3610 cells to resist predation by M. xanthus. Furthermore, purified bacillaene was added exogenously to domesticated strains, resulting in resistance to predation. Lastly, we found that M. xanthus is incapable of consuming B. subtilis spores even from laboratory strains, indicating the evolutionary fitness of sporulation as a survival strategy. Together, the results suggest that bacillaene inhibits M. xanthus predation, allowing sufficient time for development of B. subtilis spores.
PMID: 25002419 [PubMed - in process]
Chemosensory regulation of a HEAT-repeat protein couples aggregation and sporulation in Myxococcus xanthus.
J Bacteriol. 2014 Sep;196(17):3160-8
Authors: Darnell CL, Wilson JM, Tiwari N, Fuentes EJ, Kirby JR
Chemosensory systems are complex, highly modified two-component systems (TCS) used by bacteria to control various biological functions ranging from motility to sporulation. Chemosensory systems and TCS both modulate phosphorelays comprised of histidine kinases and response regulators, some of which are single-domain response regulators (SD-RRs) such as CheY. In this study, we have identified and characterized the Che7 chemosensory system of Myxococcus xanthus, a common soil bacterium which displays multicellular development in response to stress. Both genetic and biochemical analyses indicate that the Che7 system regulates development via a direct interaction between the SD-RR CheY7 and a HEAT repeat domain-containing protein, Cpc7. Phosphorylation of the SD-RR affects the interaction with its target, and residues within the α4-β5-α5 fold of the REC domain govern this interaction. The identification of the Cpc7 interaction with CheY7 extends the diversity of known targets for SD-RRs in biological systems.
PMID: 24957622 [PubMed - indexed for MEDLINE]
Functional organization of a multimodular bacterial chemosensory apparatus.
PLoS Genet. 2014 Mar;10(3):e1004164
Authors: Moine A, Agrebi R, Espinosa L, Kirby JR, Zusman DR, Mignot T, Mauriello EM
Chemosensory systems (CSS) are complex regulatory pathways capable of perceiving external signals and translating them into different cellular behaviors such as motility and development. In the δ-proteobacterium Myxococcus xanthus, chemosensing allows groups of cells to orient themselves and aggregate into specialized multicellular biofilms termed fruiting bodies. M. xanthus contains eight predicted CSS and 21 chemoreceptors. In this work, we systematically deleted genes encoding components of each CSS and chemoreceptors and determined their effects on M. xanthus social behaviors. Then, to understand how the 21 chemoreceptors are distributed among the eight CSS, we examined their phylogenetic distribution, genomic organization and subcellular localization. We found that, in vivo, receptors belonging to the same phylogenetic group colocalize and interact with CSS components of the respective phylogenetic group. Finally, we identified a large chemosensory module formed by three interconnected CSS and multiple chemoreceptors and showed that complex behaviors such as cell group motility and biofilm formation require regulatory apparatus composed of multiple interconnected Che-like systems.
PMID: 24603697 [PubMed - in process]
Menaquinone analogs inhibit growth of bacterial pathogens.
Antimicrob Agents Chemother. 2013 Nov;57(11):5432-7
Authors: Schlievert PM, Merriman JA, Salgado-Pabón W, Mueller EA, Spaulding AR, Vu BG, Chuang-Smith ON, Kohler PL, Kirby JR
Gram-positive bacteria cause serious human illnesses through combinations of cell surface and secreted virulence factors. We initiated studies with four of these organisms to develop novel topical antibacterial agents that interfere with growth and exotoxin production, focusing on menaquinone analogs. Menadione, 1,4-naphthoquinone, and coenzymes Q1 to Q3 but not menaquinone, phylloquinone, or coenzyme Q10 inhibited the growth and to a greater extent exotoxin production of Staphylococcus aureus, Bacillus anthracis, Streptococcus pyogenes, and Streptococcus agalactiae at concentrations of 10 to 200 μg/ml. Coenzyme Q1 reduced the ability of S. aureus to cause toxic shock syndrome in a rabbit model, inhibited the growth of four Gram-negative bacteria, and synergized with another antimicrobial agent, glycerol monolaurate, to inhibit S. aureus growth. The staphylococcal two-component system SrrA/B was shown to be an antibacterial target of coenzyme Q1. We hypothesize that menaquinone analogs both induce toxic reactive oxygen species and affect bacterial plasma membranes and biosynthetic machinery to interfere with two-component systems, respiration, and macromolecular synthesis. These compounds represent a novel class of potential topical therapeutic agents.
PMID: 23959313 [PubMed - indexed for MEDLINE]
Draft Genome of a Type 4 Pilus Defective Myxococcus xanthus Strain, DZF1.
Genome Announc. 2013;1(3)
Authors: Müller S, Willett JW, Bahr SM, Scott JC, Wilson JM, Darnell CL, Vlamakis HC, Kirby JR
Myxococcus xanthus is a member of the Myxococcales order within the deltaproteobacterial subdivision. Here, we report the whole-genome shotgun sequence of the type IV pilus (T4P) defective strain DZF1, which includes many genes found in strain DZ2 but absent from strain DK1622.
PMID: 23788552 [PubMed]
Draft Genome Sequence of Myxococcus xanthus Wild-Type Strain DZ2, a Model Organism for Predation and Development.
Authors: Müller S, Willett JW, Bahr SM, Darnell CL, Hummels KR, Dong CK, Vlamakis HC, Kirby JR
Myxococcus xanthus is a member of the Myxococcales order within the Deltaproteobacteria subdivision. The myxobacteria reside in soil, have relatively large genomes, and display complex life cycles. Here, we report the whole-genome shotgun sequence of strain DZ2, which includes unique genes not found previously in strain DK1622.
PMID: 23661486 [PubMed]
Genetic and biochemical dissection of a HisKA domain identifies residues required exclusively for kinase and phosphatase activities.
PLoS Genet. 2012;8(11):e1003084
Authors: Willett JW, Kirby JR
Two-component signal transduction systems, composed of histidine kinases (HK) and response regulators (RR), allow bacteria to respond to diverse environmental stimuli. The HK can control both phosphorylation and subsequent dephosphorylation of its cognate RR. The majority of HKs utilize the HisKA subfamily of dimerization and histidine phosphotransfer (DHp) domains, which contain the phospho-accepting histidine and directly contact the RR. Extensive genetics, biochemistry, and structural biology on several prototypical TCS systems including NtrB-NtrC and EnvZ-OmpR have provided a solid basis for understanding the function of HK-RR signaling. Recently, work on NarX, a HisKA_3 subfamily protein, indicated that two residues in the highly conserved region of the DHp domain are responsible for phosphatase activity. In this study we have carried out both genetic and biochemical analyses on Myxococcus xanthus CrdS, a member of the HisKA subfamily of bacterial HKs. CrdS is required for the regulation of spore formation in response to environmental stress. Following alanine-scanning mutagenesis of the α1 helix of the DHp domain of CrdS, we determined the role for each mutant protein for both kinase and phosphatase activity. Our results indicate that the conserved acidic residue (E372) immediately adjacent to the site of autophosphorylation (H371) is specifically required for kinase activity but not for phosphatase activity. Conversely, we found that the conserved Thr/Asn residue (N375) was required for phosphatase activity but not for kinase activity. We extended our biochemical analyses to two CrdS homologs from M. xanthus, HK1190 and HK4262, as well as Thermotoga maritima HK853. The results were similar for each HisKA family protein where the conserved acidic residue is required for kinase activity while the conserved Thr/Asn residue is required for phosphatase activity. These data are consistent with conserved mechanisms for kinase and phosphatase activities in the broadly occurring HisKA family of sensor kinases in bacteria.
PMID: 23226719 [PubMed - indexed for MEDLINE]
CrdS and CrdA comprise a two-component system that is cooperatively regulated by the Che3 chemosensory system in Myxococcus xanthus.
Myxococcus xanthus serves as a model organism for development and complex signal transduction. Regulation of developmental aggregation and sporulation is controlled, in part, by the Che3 chemosensory system. The Che3 pathway consists of homologs to two methyl-accepting chemotaxis proteins (MCPs), CheA, CheW, CheB, and CheR but not CheY. Instead, the output for Che3 is the NtrC homolog CrdA, which functions to regulate developmental gene expression. In this paper we have identified an additional kinase, CrdS, which directly regulates the phosphorylation state of CrdA. Both epistasis and in vitro phosphotransfer assays indicate that CrdS functions as part of the Che3 pathway and, in addition to CheA3, serves to regulate CrdA phosphorylation in M. xanthus. We provide kinetic data for CrdS autophosphorylation and demonstrate specificity for phosphotransfer from CrdS to CrdA. We further demonstrate that CheA3 destabilizes phosphorylated CrdA (CrdA~P), indicating that CheA3 likely acts as a phosphatase. Both CrdS and CheA3 control developmental progression by regulating the phosphorylation state of CrdA~P in the cell. These results support a model in which a classical two-component system and a chemosensory system act synergistically to control the activity of the response regulator CrdA. IMPORTANCE While phosphorylation-mediated signal transduction is well understood in prototypical chemotaxis and two-component systems (TCS), chemosensory regulation of alternative cellular functions (ACF) has not been clearly defined. The Che3 system in Myxococcus xanthus is a member of the ACF class of chemosensory systems and regulates development via the transcription factor CrdA (chemosensory regulator of development) (K. Wuichet and I. B. Zhulin, Sci. Signal. 3:ra50, 2010; J. R. Kirby and D. R. Zusman, Proc. Natl. Acad. Sci. U. S. A. 100:2008-2013, 2003). We have identified and characterized a homolog of NtrB, designated CrdS, capable of specifically phosphorylating the NtrC homolog CrdA in M. xanthus. Additionally, we demonstrate that the CrdSA two-component system is negatively regulated by CheA3, the central processor within the Che3 system of M. xanthus. To our knowledge, this study provides the first example of an ACF chemosensory system regulating a prototypical two-component system and extends our understanding of complex regulation of developmental signaling pathways.
PMID: 21810965 [PubMed - indexed for MEDLINE]
Deciphering the hunting strategy of a bacterial wolfpack.
FEMS Microbiol Rev. 2009 Sep;33(5):942-57
Authors: Berleman JE, Kirby JR
Myxococcus xanthus is a common soil bacterium with an intricate multicellular lifestyle that continues to challenge the way in which we conceptualize the capabilities of prokaryotic organisms. Myxococcus xanthus is the preferred laboratory representative from the Myxobacteria, a family of organisms distinguished by their ability to form highly structured biofilms that include tentacle-like packs of surface-gliding cell groups, synchronized rippling waves of oscillating cells and massive spore-filled aggregates that protrude upwards from the substratum to form fruiting bodies. But most of the Myxobacteria are also predators that thrive on the degradation of macromolecules released through the lysis of other microbial cells. The aim of this review is to examine our understanding of the predatory life cycle of M. xanthus. We will examine the multicellular structures formed during contact with prey, and the molecular mechanisms utilized by M. xanthus to detect and destroy prey cells. We will also examine our understanding of microbial predator-prey relationships and the prospects for how bacterial predation mechanisms can be exploited to generate new antimicrobial technologies.
PMID: 19519767 [PubMed - indexed for MEDLINE]
Chemotaxis-like regulatory systems: unique roles in diverse bacteria.
Annu Rev Microbiol. 2009;63:45-59
Authors: Kirby JR
Bacteria sense the chemical world using a variety of mechanisms that include the frequently described two-component system (TCS), which comprises a sensor kinase and response regulator, to regulate gene expression in response to environmental cues. One of the best and most widely studied versions of the TCS is the system that controls chemotaxis in Escherichia coli. The chemotaxis machinery includes components not found in other TCS to regulate motility and is therefore an exception to the rule for two-component signaling. The hallmark feature of the chemotaxis system is the presence of an adaptation module in which the sensor receptor protein is posttranslationally modified to attenuate ligand-induced signaling, a mechanism not yet identified for the more widely distributed prototypical TCS. More recently, variations on the chemotaxis system itself have been identified and they are termed chemosensory systems and are the subject of this review. Extensive research has provided a perspective on TCS signaling and indicates that variation and diversity for the standard two-component system are predominant in the microbial world.
PMID: 19379070 [PubMed - indexed for MEDLINE]
Predataxis behavior in Myxococcus xanthus.
Proc Natl Acad Sci U S A. 2008 Nov 4;105(44):17127-32
Authors: Berleman JE, Scott J, Chumley T, Kirby JR
Spatial organization of cells is important for both multicellular development and tactic responses to a changing environment. We find that the social bacterium, Myxococcus xanthus utilizes a chemotaxis (Che)-like pathway to regulate multicellular rippling during predation of other microbial species. Tracking of GFP-labeled cells indicates directed movement of M. xanthus cells during the formation of rippling wave structures. Quantitative analysis of rippling indicates that ripple wavelength is adaptable and dependent on prey cell availability. Methylation of the receptor, FrzCD is required for this adaptation: a frzF methyltransferase mutant is unable to construct ripples, whereas a frzG methylesterase mutant forms numerous, tightly packed ripples. Both the frzF and frzG mutant strains are defective in directing cell movement through prey colonies. These data indicate that the transition to an organized multicellular state during predation in M. xanthus relies on the tactic behavior of individual cells, mediated by a Che-like signal transduction pathway.
PMID: 18952843 [PubMed - indexed for MEDLINE]
Multicellular development in Myxococcus xanthus is stimulated by predator-prey interactions.
J Bacteriol. 2007 Aug;189(15):5675-82
Myxococcus xanthus is a predatory bacterium that exhibits complex social behavior. The most pronounced behavior is the aggregation of cells into raised fruiting body structures in which cells differentiate into stress-resistant spores. In the laboratory, monocultures of M. xanthus at a very high density will reproducibly induce hundreds of randomly localized fruiting bodies when exposed to low nutrient availability and a solid surface. In this report, we analyze how M. xanthus fruiting body development proceeds in a coculture with suitable prey. Our analysis indicates that when prey bacteria are provided as a nutrient source, fruiting body aggregation is more organized, such that fruiting bodies form specifically after a step-down or loss of prey availability, whereas a step-up in prey availability inhibits fruiting body formation. This localization of aggregates occurs independently of the basal nutrient levels tested, indicating that starvation is not required for this process. Analysis of early developmental signaling relA and asgD mutants indicates that they are capable of forming fruiting body aggregates in the presence of prey, demonstrating that the stringent response and A-signal production are surprisingly not required for the initiation of fruiting behavior. However, these strains are still defective in differentiating to spores. We conclude that fruiting body formation does not occur exclusively in response to starvation and propose an alternative model in which multicellular development is driven by the interactions between M. xanthus cells and their cognate prey.
PMID: 17513469 [PubMed - indexed for MEDLINE]