Bacillus licheniformis escapes from Myxococcus xanthus predation by deactivating myxovirescin A through enzymatic glucosylation

Myxococcus xanthus kills susceptible bacteria using myxovirescin A (TA) during predation. However, whether prey cells in nature can escape M. xanthus by developing resistance to TA is unknown. We observed that many field-isolated Bacillus licheniformis strains could survive encounters with M. xanthus, which was correlated to their TA resistance. A TA glycoside was identified in the broth of predation-resistant B. licheniformis J32 co-cultured with M. xanthus, and a glycosyltransferase gene (yjiC) was up-regulated in J32 after the addition of TA. Hetero-expressed YjiC-modified TA to a TA glucoside (TA-Gluc) by conjugating a glucose moiety to the C-21 hydroxyl group, and the resulting compound was identical to the TA glycoside present in the co-culture broth. TA-Gluc exhibited diminished bactericidal activity due to its weaker binding with LspA, as suggested by in silico docking data. Heterologous expression of the yjiC gene conferred both TA and M. xanthus-predation resistance to the host Escherichia coli cells. Furthermore, under predatory pressure, B. licheniformis Y071 rapidly developed predation resistance by acquiring TA resistance through the overexpression of yjiC and lspA genes. These results suggest that M. xanthus predation resistance in B. licheniformis is due to the TA deactivation by glucosylation, which is induced in a predator-mediated manner.     

Genetic Redundancy,Proximity, and Functionality of lspA,the Target of Antibiotic TA,in the Myxococcus xanthus Producer Strain

We recently showed that type II signal peptidase (SPaseII) encoded by lspA is the target of an antibiotic called TA (myxovirescin), which is made by Myxococcus xanthus. SPaseII cleaves the signal peptide during bacterial lipoprotein processing. Bacteria typically contain one lspA gene; however, strikingly, the M. xanthus DK1622 genome contains four (lspA1 to lspA4). Since two of these genes, lspA3 and lspA4, are located in the giant TA biosynthetic gene cluster, we hypothesized they may play a role in TA resistance. To investigate the functions of the four M. xanthus lspA (lspA^Mx) genes, we conducted sequence comparisons and found that they contained nearly all the conserved residues characteristic of SPaseII family members. Genetic studies found that an Escherichia coli ΔlspA mutation could be complemented by any of the lspA^Mx genes in an lpp mutant background, but not in an E. coli lpp⁺ background. Because Lpp is the most abundant E. coli lipoprotein, these results suggest the M. xanthus proteins do not function as efficiently as the host enzyme. In E. coli, overexpression of each of the LspA^Mx proteins conferred TA and globomycin resistance, although LspA3 conferred the highest degree of resistance. In M. xanthus, each lspA^Mx gene could be deleted and was therefore dispensable for growth. However, lspA3 or lspA4 deletion mutants each exhibited a tan phase variation bias, which likely accounts for their reduced-swarming and delayed-development phenotypes. In summary, we propose that all four LspA^Mx proteins function as SPaseIIs and that LspA3 and LspA4 might also have roles in TA resistance and regulation, respectively.     

Isolation and characterization of new bacteriophages for Myxococcus xanthus

Bacteriophages for Myxococcus xanthus of similar morphology to phage Mx4 were isolated from cultures of a variety of myxobacterial species. Phages similar to Mx1 and Mx8 were obtained by infecting M. xanthus with one of the phages of the Mx4 group that had been treated with either UV light or a chemical mutagen.The DNA molecules from the phages were characterized by electron microscopy. One phage, Mx113, contains an unusual type of terminal redundancy revealed by examination of denatured and re-annealed DNA.Several of the phages of the Mx4 group and the other two new phages, Mx113 and Mx811, were found capable of transducing genetic markers in M. xanthus.One phage, Mx416, was characterized in more detail. It establishes true lysogens in M. xanthus; the phage plaques on both a non-motile mutant and also on a wild-type host although it is restricted in the latter.We dedicate this paper to Professor Dr. Hans Kühlwein in the year of his retirement and in recognition of his many contributions to the study of Myxobacteria     

Production and characterization of the milk-clotting protease of<Emphasis Type="Italic"> Myxococcus xanthus</Emphasis> strain 422

The cheese industry is seeking novel sources of enzymes for cheese production. Microbial rennets have several advantages over animal rennets. (1) They are easy to generate and purify and do not rely on the availability of animal material. (2) The production of microbial clotting enzymes may be improved by biotechnological techniques. In this work, the biochemical characterization of a novel milk-clotting extracellular enzyme from Myxococcus xanthus strain 422 and a preliminary evaluation of its cheese-producing ability are reported. Strain 422 was selected from four M. xanthus strains as the best producer of extracellular milk-clotting activity, based on both its enzyme yield and specific milk-clotting activity, which also afforded lower titration values than enzymes from the three other M. xanthus strains. The active milk-clotting enzyme from M. xanthus strain 422 is a true milk-clotting enzyme with a molecular mass of 40 kDa and a pI of 5.0. Highest milk-clotting activity was at pH 6 and 37 °C. The enzyme was completely inactivated by heating for 12 min at 65 °C. The crude enzyme preparation was resolved by anion-exchange chromatography into two active fractions that were tested in cheese production assays of compositional (dry matter, fat content, fat content/dry-matter ratio, and moisture-non-fat content) and physicochemical properties (firmness, tensile strength, pH and Aw) of the milk curds obtained. Purified protein fraction II exhibited a significantly higher milk-clotting ability than either protein fraction I or a total protein extract, underlining the potential usefulness of M. xanthus strain 422 as a source of rennet for cheese production.     

Entrapment and lysis of the cyanobacterium Phormidium luridum by aqueous colonies of Myxococcus xanthus PCO2

A Myxococcus xanthus isolate from a farm drainage ditch, designated strain PCO2, is capable of rapidly inducing lysis of both agar and liquid-grown cultures of the cyanobacterium, Phormidium luridum, var. olivacea. Microscopic studies of the predator-prey interaction demonstrate that lysis of the cyanobacterium occurs within clumps and spherules formed by the cells of M. xanthus PCO2. In the earliest stage, one sees the formation of irregular microclumps of bacteria and cyanobacterial filaments. As these clumps mature, colonies 1 to 6 mm in diameter develops. The center of these densely green colonies contains cyanohacteria in various stages of degradation, while the periphery is almost exclusively a tightly woven mass of myxobacterial cells. Electron microscopy shows that long extrusions from the outer membrane of the M. xanthus PCO2 cells are involved in the formation both of initial clumps and of mature colonial spherules. These extrusions appear to efficiently entangle the cyanobacterial filaments in the culture environment. Predator-to-prey ratios of 1/10, 1/100 and 1/1,000 have resulted in cyanobacterial lysis. Because the entrapment and lysis of P. luridum filaments by M. xanthus PCO2 appears to be independent of any other heterotrophic nutritional requirement, as well as of environmental agitation, this system has potential as a biological control technique for undesirable aquatic cyanobacteria.Abbreviations TEM transmission electron microscopy - SEM scanning electron microscopy - AB algae broth - ABT algae broth plus 0.2% tryptone     

Experimental social evolution with Myxococcus xanthus

Genetically-based social behaviors are subject to evolutionary change in response to natural selection. Numerous microbial systems provide not only the opportunity to understand the genetic mechanisms underlying specific social interactions, but also to observe evolutionary changes in sociality over short time periods. Here we summarize experiments in which behaviors of the social bacterium Myxococcus xanthus changed extensively during evolutionary adaptation to two relatively asocial laboratory environments. M. xanthus moves cooperatively, exhibits cooperative multicellular development upon starvation and also appears to prey cooperatively on other bacteria. Replicate populations of M. xanthus were evolved in both structured (agar plate) and unstructured (liquid) environments that contained abundant resources. The importance of social cooperation for evolutionary fitness in these habitats was limited by the absence of positive selection for starvation-induced spore production or predatory efficiency. Evolved populations showed major losses in all measured categories of social proficiency- motility, predation, fruiting ability, and sporulation. Moreover, several evolved genotypes were observed to exploit the social behavior of their ancestral parent when mixed together during the developmental process. These experiments that resulted in both socially defective and socially exploitative genotypes demonstrate the power of laboratory selection experiments for studying social evolution at the microbial level. Results from additional selection experiments that place positive selection pressure on social phenotypes can be integrated with direct study of natural populations to increase our understanding of principles that underlie the evolution of microbial social behavior. This revised version was published online in August 2006 with corrections to the Cover Date.     

Silver Sorption to Myxococcus xanthus Biomass

This paper deals with silver sorption to Myxococcus xanthus biomass. The dry biomass of this microorganism is shown to be a good sorbent for the recovery of silver present at low solution concentrations. Between initial silver concentrations of 2 and 0.05 mM, the percentage of accumulation ranges from 8.12% to 75% of the total silver present in the solution. Transmission electron microscopy study of M. xanthus wet biomass after silver accumulation shows the sorption within the extracellular polysaccharide, on the cell wall, and in the cytoplasm. The presence of silver deposits in the cytoplasm indicates that at least two mechanisms are involved in silver sorption by this bacterium biomass. First, silver was bound to the cell surface and extracellular polysaccharide, and second, a silver intracellular deposition process took place. The higher amount of silver deposits in the extracellular polysaccharide, present abundantly in M. xanthus cells, explains the capacity of this bacterium to bind silver efficiently. The results obtained indicate that the removal of silver by M. xanthus from the diluted solutions could be used in recycling this valuable metal. One interesting observation of this investigation is the crystalline form, possibly as chlorargyrite, in which the silver deposits are found in the M. xanthus cells.     

Fibrils as extracellular appendages of bacteria: Their role in contact-mediated cell-cell interactions in Myxococcus xanthus

Social behavior in the myxobacterium Myxococcus xanthus involves epicellular, peritrichous appendages called fibrils. These are polysaccharide organelles containing a set of tightly adhering proteins. It is proposed that cell-cell contact is perceived by the fibrils and is mediated by the action of a fibrillar ADP-ribosyl transferase. Fibrils or fibril-like organelles have also been found on a variety of other gram-negative bacteria and at least one archaeon, and may mediate cell-cell contact between the bacteria themselves or between the bacteria and their eukaryotic host cells. BioEssays 21:590–595, 1999. © 1999 John Wiley & Sons, Inc.     

Assimilatory sulfur metabolism in marine microorganisms: Sulfur metabolism,growth, and protein synthesis of Pseudomonas halodurans and Alteromonas luteo-violaceus during sulfate limitation

Sulfate concentration in the growth medium exerted a strong influence on the sulfur content of protein in two marine bacteria, Pseudomonas halodurans and Alteromonasluteo-violaceus, but the distribution of sulfur in major biochemical fractions was not affected. 90% of the total cellular sulfur was contained in low molecular weight organic compounds and protein; inorganic sulfate was not an important component. The sulfur content of isolated protein and total cellular sulfur increased in proportion to the external sulfate concentration for both bacteria, reaching a maximum at about 100–250 M. The growth rate of P. halodurans only was dependent on the sulfate concentration.Sulfur starvation of cells labeled to equilibrium with ³⁵S-sulfate resulted in a rapid decrease in low molecular weight organic S with a concommitant increase in alcohol soluble (P. halodurans) or residue protein (A. luteo-violaceus). Although cell division was prevented, total protein increased in both bacteria, resulting in synthesis of sulfur-deficient protein. This effect was most pronounced in P. halodurans.Addition of ³⁵S-sulfate to sulfur-starved A. luteo-violaceus further demonstrated that sulfur metabolism was restricted primarily to the synthesis and utilization of sulfurcontaining protein precursors. The low molecular weight organic S pool was replenished rapidly, and the pool size per cell reached twice the normal value before cell division resumed. Incorporation into protein was very rapid.Abbreviations L.M.W. low molecular weight - TCA trichloroacetic acid     

phoR1, a gene encoding a new histidine protein kinase Myxococcus xanthus

A soil bacterium able to undergo multicellular development and a coordinated gliding in swarms, requires an accurate regulatory network of phosphorelay proteins. Inorganic phosphate is a limiting nutrient in soil and its importance in regulation is critical. As a step towards studying phosphate regulation and its influence in the developmental process in this bacterium, we screened a Myxococcus xanthus library for clones with phosphatase activity, and found four different ones. The deduced sequence of one of the cloned inserts is similar to that of the classic transmembrane histidine protein kinase of the sensor family of the two-component signal transduction systems with a high sequence similarity to the sensor kinase in the Pho regulon of Bacillus subtilis PhoR. This gene has been named phoR1 and its deduced amino acid sequence consists of 455 residues with a predicted molecular mass of 48.5 kDa. The M. xanthus PhoR1 deduced sequence contains all the characteristic histidine protein kinase motifs in the same order and with the same spacing. A hydropathy profile indicates two membrane-spanning segments located at the extreme N-terminus, according to the putative sensor role of this domain. A gene-disrupted mutant is unable to produce normal mature fruiting bodies and produces fewer spores. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dominant chloramphenicol-resistant bacteria and resistance genes in coastal marine waters of Jiaozhou Bay,China

Studies of abundance, diversity and distribution of antibiotic-resistant bacteria and their resistance determinants are necessary for effective prevention and control of antibiotic resistance and its dissemination, critically important for public health and environment management. In order to gain an understanding of the persistence of resistance in the absence of a specific antibiotic selective pressure, microbiological surveys were carried out to investigate chloramphenicol-resistant bacteria and the chloramphenicol acetyltransferase resistance genes in Jiaozhou Bay after chloramphenicol was banned since 1999 in China. About 0.15–6.70% cultivable bacteria were chloramphenicol resistant, and the highest abundances occurred mainly in the areas near river mouths or sewage processing plants. For the dominant resistant isolates, 14 genera and 25 species were identified, mostly being indigenous estuarine or marine bacteria. Antibiotic-resistant potential human or marine animal pathogens, such as Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Shewanella algae, were also identified. For the molecular resistance determinants, the cat I and cat III genes could be detected in some of the resistant strains, and they might have the same origins as those from clinical strains as determined via gene sequence analysis. Further investigation about the biological, environmental and anthropogenic mechanisms and their interactions that may contribute to the persistence of antibiotic-resistance in coastal marine waters in the absence of specific antibiotic selective pressure is necessary for tackling this complicated environmental issue.     

Branched-chain fatty acids: the case for a novel form of cell-cell signalling during Myxococcus xanthus development

The esg locus is required for the formation of muiti-cellular fruiting bodies and spores by the developmental bacterium Myxococcus xanthus Studies have suggested that esg mutants are defective in the production of an essential signal (E-signal) used in cell-cell communication and that E-signalling is required for the expression of many developmental genes. Recently we have determined that the esg locus encodes components of a branched-chain keto acid dehydrogenase. a multienzyme complex involved in branched-chain amino acid metabolism in many bacteria and higher organisms. During vegetative growth in M. xanthus. this enzyme complex appears to participate in the production of the branched-chain fatty acids found in this organism. M. xanthus fatty acids (including the branched-chain fatty acids) have been observed to have a variety of effects on developing cells. These effects include; (i) the lysis of M. xanthus cells (autocide activity), (ii) acceleration of the rate of sporulation and (iii) rescue of sporulation by certain development-defective mutants. These and other results suggest a model in which the branched-chain fatty acids. Synthesized during growth, are released from cellular phospholipid by a developmentally regulated phospholipase during fruiting-body formation. This model proposes that one or more of the branched-chain fatty acids that are released constitutes the E-signal which must be transmitted between cells to complete M. xanthus development.     

Antibiotic Production by Myxobacteria Plays a Role in Predation

Myxobacteria are predatory and are prolific producers of secondary metabolites. Here, we tested a hypothesized role that secondary metabolite antibiotics function as weapons in predation. To test this, a Myxococcus xanthus Δta1 mutant, blocked in antibiotic TA (myxovirescin) production, was constructed. This TA⁻ mutant was defective in producing a zone of inhibition (ZOI) against Escherichia coli. This shows that TA is the major M. xanthus-diffusible antibacterial agent against E. coli. Correspondingly, the TA⁻ mutant was defective in E. coli killing. Separately, an engineered E. coli strain resistant to TA was shown to be resistant toward predation. Exogenous addition of spectinomycin, a bacteriostatic antibiotic, rescued the predation defect of the TA⁻ mutant. In contrast, against Micrococcus luteus the TA⁻ mutant exhibited no defect in ZOI or killing. Thus, TA plays a selective role on prey species. To extend these studies to other myxobacteria, the role of antibiotic corallopyronin production in predation was tested and also found to be required for Corallococcus coralloides killing on E. coli. Next, a role of TA production in myxobacterial fitness was assessed by measuring swarm expansion. Here, the TA⁻ mutant had a specific swarm rate reduction on prey lawns, and thus reduced fitness, compared to an isogenic TA⁺ strain. Based on these observations, we conclude that myxobacterial antibiotic production can function as a predatory weapon. To our knowledge, this is the first report to directly show a link between secondary metabolite production and predation.     

Molecular phylogenetic analyses reveal a close relationship between powdery mildew fungi on some tropical trees and Erysiphe alphitoides, an oak powdery mildew

To investigate the phylogenetic relationships among the powdery mildew fungi of some economically important tropical trees belonging to Oidium subgenus Pseudoidium, we conducted molecular phylogenetic analyses using 30 DNA sequences of the rDNA internal transcribed spacer (ITS) regions and 26 sequences of the domains D1 and D2 of the 28S rDNA obtained from the powdery mildews on Hevea brasiliensis (para rubber tree), Anacardium occidentale (cashew), Bixa orellana, Citrus spp., Mangifera indica (mango), and Acacia spp. The results indicate that the powdery mildew fungi isolated from these tropical trees are closely related to one another. These powdery mildews are also closely related to E. alphitoides (including Erysiphe sp. on Quercus phillyraeoides). Because of the obligate biotrophic nature of the powdery mildew fungi, the relationship between powdery mildews and their host plants is conservative. However, the present study suggests that a particular powdery mildew species has expanded its host ranges on a wide range of the tropical trees. This article also suggests that a powdery mildew fungus distributed in temperate regions of the Northern Hemisphere expanded its host ranges onto tropical plants and may be a good example of how geographical and host range expansion has occurred in the Erysiphales.     

Easel, a gypsy LTR-retrotransposon in the Salmonidae

Despite the close similarities between retroviruses and the gypsy/Ty3 group of LTR-retrotransposons their host ranges are largely distinct: the retroviruses are found only in vertebrates, whereas the gypsy LTR-retrotransposons are almost exclusively restricted to invertebrates, plants and fungi. Here we report the amplification by PCR, and characterisation, of one of the first LTR-retrotransposons to be discovered in vertebrates - in several members of the piscine family Salmonidae. Phylogenetic analysis of this retroelement, termed easel, indicates that it is probably a phylogeneticaly basal member of the gypsy group of LTR-retrotransposons and occurs in some of the same species from which retroviruses have previously been isolated. Thus some members of the Salmonidae are the first organisms known to harbour both retroviral branch elements and the gypsy LTR-retrotransposon branch elements. This creates an overlap in the host ranges of the two retroelement families.     

Resistance mechanisms in protoporphyrinogen oxidase (PROTOX) inhibitor-resistant transgenic rice

We investigated the mechanism for conferring herbicide resistance in transgenic rice. Plants from Line M4 were resistant to PROTOX inhibitors and had yields similar to those from wild-type (WT) rice.Myxococcus xanthus PROTOX mRNA was abundantly expressed in the transgenic leaf tissues, and theM. xanthus PROTOX gene was stably transmitted into the T₄ generation. We detected a protein with a predicted molecular mass of 50 kD, equal to the weight ofM. xanthus PROTOX, in M4 but not WT plants. Furthermore, several PROTOX-inhibitor herbicides — acifluorfen, oxyfluorfen, carfentrazone-ethyl, and oxadiazon — caused significant cellular leakage and lipid peroxidation in the WT, but not in the transgenics. Total PROTOX activity in untreated transformed rice was 17-fold higher than in the WT, with activity being inhibited in the latter genotype by 55%, 59%, 53%, or 60% as a result of treatment with acifluorfen, oxyfluorfen, carfentrazone-ethyl, or oxadiazon, respectively. However, PROTOX activities in transgenic rice were similar to their corresponding, untreated controls. The accumulation of Proto IX was 15-to 21-fold higher in the WT than in M4 when plants were treated with PROTOX inhibitors. In the former, their epicuticular wax and chloroplasts were severely damaged after oxyfluorfen treatment The lack of damage in transformed plants suggests that M4 does not accumulate Proto IX, probably due to the production of herbicide-resistant chloroplastic and mitochondria PROTOX.     

Structural differentiation of microhabitats of sympatricmacaca fascicularis andM. nemestrina in East Kalimantan,Indonesia

Macaca nemestrina andM. fascicularis coexist through much of their geographic ranges in Southeast Asia, but locally they segregate into drier hilly terrain and wetter alluvial riverine terrain respectively. SinceM. fascicularis travel arboraally andM. nemestrina, travel terrestrially, structural characteristics of habitats on the two different substrates may explain local segregation of these two species. This paper reports measures comparing habitat structure ofM. fascicularis fascicularis andM. nemestrina nemestrina at the Mentoko site in East Kalimantan, Indonesia. Results show that (1) ground cover is thicker; (2) there are fewer gaps in the canopy; and (3) the foliage of the canopy is more dense in habitat occupied by arborealM. f. fascicularis than in habitat occupied byM. n. nemestrina. These differences in habitat structure appear to explain segregation of the two species at the Mentoko. Similar differences in habitat may permit coexistence of the two species throughout their geographical ranges.     

Investigation of polyethylenimine‐grafted‐triamcinolone acetonide as nucleus‐targeting gene delivery systems

Background

Nuclear membrane is one of the main barriers in polymer mediated intracellular gene delivery. To improve the transgenic activity and safety of nonviral vector, triamcinolone acetonide (TA) as a nuclear localization signal was conjugated with different molecular weight polyethylenimine (PEI).

Methods

Different molecular weight PEI [600, 1800, 25 000 (25k)] was conjugated with TA to synthesize PEI‐TA by two‐step reaction. Their physicochemical characteristics, in vitro cytotoxicity and transfection efficiency were evaluated. To investigate the difference of transfection efficiency of various molecular weight PEI‐TA, their transfection mechanism was further investigated by confocal microscopy and competition assay. Transgenic expression in vivo was evaluated by injection into hepatic portal vein of mice.

Results

All PEI‐TA could form nanosize polyplexes with DNA and their physicochemical properties resemble each other. Their cytotoxicities were negligible compared to PEI 25k. The order of transfection efficiency was PEI 1800‐TA > PEI 600‐TA > PEI 25k‐TA. A transfection mechanism study displayed that TA could inhibit considerably the transgenic activity of PEI 1800‐TA and PEI 600‐TA, but that of PEI 25k‐TA was not inhibited. It was suggested that PEI 1800‐TA and PEI 600‐TA might translocate into the nucleus. Confocal microscopy investigation verified this suggestion. The data strongly suggested that the transfection efficiency of PEI 1800‐TA in vivo was much higher than that of PEI 25k, which was consistent with the results obtained in vitro.

Conclusions

Low molecular weight PEI‐TA could translocate into the nucleus efficiently. PEI 1800‐TA presented higher transgenic activity and it has a great potential for gene therapy as a nonviral carrier. Copyright © 2010 John Wiley & Sons, Ltd.     

Killing of Escherichia coli by Myxococcus xanthus in Aqueous Environments Requires Exopolysaccharide-Dependent Physical Contact

Nutrient or niche-based competition among bacteria is a widespread phenomenon in the natural environment. Such interspecies interactions are often mediated by secreted soluble factors and/or direct cell–cell contact. As ubiquitous soil bacteria, Myxococcus species are able to produce a variety of bioactive secondary metabolites to inhibit the growth of other competing bacterial species. Meanwhile, Myxococcus spp. also exhibit sophisticated predatory behavior, an extreme form of competition that is often stimulated by close contact with prey cells and largely depends on the availability of solid surfaces. Myxococcus spp. can also be isolated from aquatic environments. However, studies focusing on the interaction between Myxococcus and other bacteria in such environments are still limited. In this study, using the well-studied Myxococcus xanthus DK1622 and Escherichia coli as model interspecies interaction pair, we demonstrated that in an aqueous environment, M. xanthus was able to kill E. coli in a cell contact-dependent manner and that the observed contact-dependent killing required the formation of co-aggregates between M. xanthus and E. coli cells. Further analysis revealed that exopolysaccharide (EPS), type IV pilus, and lipopolysaccharide mutants of M. xanthus displayed various degrees of attenuation in E. coli killing, and it correlated well with the mutants' reduction in EPS production. In addition, M. xanthus showed differential binding ability to different bacteria, and bacterial strains unable to co-aggregate with M. xanthus can escape the killing, suggesting the specific nature of co-aggregation and the targeted killing of interacting bacteria. In conclusion, our results demonstrated EPS-mediated, contact-dependent killing of E. coli by M. xanthus, a strategy that might facilitate the survival of this ubiquitous bacterium in aquatic environments.