Myxococcus Xanthus DK1622 Research Articles

Understanding the population dynamics of organisms exposed to the predatory activity of myxobacteria

Predatory myxobacteria have an antimicrobial nature that dominates their interactions with neighbouring organisms. They are abundantly found in soil, water, dung of herbivores, and have the potential to significantly affect the microbiome of an environment. In this project, we hypothesize that potential prey organisms evolve in response to the selective pressure exerted by predatory microbes. Using a variety of nutrient media, we isolated bacteria from soil samples to test their susceptibility and resistance to the laboratory strain Myxococcus xanthus DK1622 and its predatory secreted outer membrane vesicles (OMVs). Soil (with and without heat treatment) was spread onto plates which had been pre-inoculated with myxobacteria, OMVs, or no pre-treatment. Plates with myxobacteria lawns or OMVs exhibited reduced diversity of isolates compared to control plates. The yield and diversity of isolates obtained also depended on the media used. Heat pre-treated soil gave rise to distinct morphologies and fewer slime producers. Co-existence and competition were exhibited by soil isolates, which were identified using 16S rRNA gene sequencing and phylogenetic analysis. Purified isolates were also characterised for their resistance and/or susceptibility to predatory attack by a variety of myxobacteria. The bacterial isolates obtained varied when exposed to seven different myxobacteria predators. Our data suggest that the addition of myxobacteria to isolation plates biases isolation towards relatively predation-resistant prey organisms. Our next goal is to isolate myxobacterial predators from the same soil samples (on different prey isolates) and test predator-prey interactions quantitative using pure strains. The genetic basis of differential predatory activity and prey susceptibility can then be investigated.

Genome Editing in Model Strain Myxococcus xanthus DK1622 by a Site-Specific Cre/loxP Recombination System.

Myxococcus xanthus DK1622 is a rich source of novel secondary metabolites, and it is often used as an expression host of exogenous biosynthetic gene clusters. However, the frequency of obtaining large genome-deletion variants by using traditional strategies is low, and progenies generated by homologous recombination contain irregular deletions. The present study aims to develop an efficient genome-engineering system for this bacterium based on the Cre/loxP system. We first verified the functionality of the native cre system that was integrated into the chromosome with an inducible promoter PcuoA. Then we assayed the deletion frequency of 8-bp-spacer-sequence mutants in loxP by Cre recombinase which was expressed by suicide vector pBJ113 or self-replicative vector pZJY41. It was found that higher guanine content in a spacer sequence had higher deletion frequency, and the self-replicative vector was more suitable for the Cre/loxP system, probably due to the leaky expression of inducible promoter PcuoA. We also inspected the effects of different antibiotics and the native or synthetic cre gene. Polymerase chain reaction (PCR) and sequencing of new genome joints confirmed that the Cre/loxP system was able to delete a 466 kb fragment in M. xanthus. This Cre/loxP-mediated recombination could serve as an alternative genetic manipulation method.

CIRCE element evolved for the coordinated transcriptional regulation of bacterial duplicate groELs

Chaperonin groEL genes are duplicated in approximately 20% of bacteria, and the duplicates are differentially transcribed due to their divergent functions. The coordinated regulation of this differential transcription is as yet undetermined. In this study, we reported that the controlling inverted repeat of chaperone expression (CIRCE) element (the HrcA-binding site located upstream of the promoter) evolved for the transcriptional regulation of duplicate groELs. CIRCE composition and locations were found to be phylogenetically conserved in bacterial taxa. Myxococcus xanthus DK1622 has two CIRCE elements (CIRCE1groESL1 and CIRCE2groESL1) in the promoter region of groESL1 and one CIRCE element (CIRCEgroEL2) before groEL2. We also found that negative HrcA and positive σ32 regulators coordinated the transcription of duplicate groELs, and that the double deletion in DK1622 eliminated transcriptional differences and reduced the heat-shock responses of groELs. In vitro binding assays showed that HrcA protein binding was biased towards CIRCE1groESL1, followed by CIRCEgroEL2, but that HrcA proteins failed to bind with CIRCE2groESL1. Mutation experiments revealed that single-nucleotide mutations in the inverted repeat regions changed the HrcA-binding abilities of CIRCEs. We constructed an in vivo transcription-regulation system in Escherichia coli to pair each of the regulators with a groEL promoter. The results indicated that the transcriptional regulation performed by HrcA and σ32 was biased towards the groEL2 and groEL1 promoters, respectively. Based on promoter-sequence characteristics, we proposed a model of the coordinated regulation of the transcription of duplicate groELs in M. xanthus DK1622.

A nuclease-toxin and immunity system for kin discrimination in Myxococcus xanthus.

The use of toxin to attack neighbours and immunity proteins to protect against toxin has been observed in bacterial conflicts, including kin discrimination. Here, we report a novel nuclease-toxin and its immunity protein function in the colony-merger incompatibility, a kind of bacterial kin discrimination, in Myxococcus xanthus DK1622. The MXAN_0049 gene was determined to be a genetic determinant for colony-merger incompatibility, and the incompatibility could be eliminated by deletion of the upstream co-transcribed MXAN_0050 gene. We demonstrated that the MXAN_0050 protein was a nuclease, and MXAN_0049 protein was able to bind to MXAN_0050 to block nuclease activity in vitro. Expression of MXAN_0050 in Escherichia coli inhibited cellular growth, and the inhibition effect could be recovered by co-expression of MXAN_0049. We found that deletion of the PAAR-encoding gene (MXAN_0044) or the type VI secretion system led to the colony-merger and co-existence with the ΔMXAN_0049 mutant, suggesting that they were associated with colony-merger incompatibility. Homologues of the nuclease-toxin and cognate immunity pair are widely distributed in bacteria. We propose a simplified model to explain the kin discrimination mechanism mediated by the nuclease-toxin and immunity protein.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.

Competitive Interactions Between Incompatible Mutants of the Social Bacterium Myxococcus xanthus DK1622.

Due to the high similarity in their requirements for space and food, close bacterial relatives may be each other's strongest competitors. Close bacterial relatives often form visible boundaries to separate their swarming colonies, a phenomenon termed colony-merger incompatibility. While bacterial species are known to have many incompatible strains, it is largely unclear which traits lead to multiple incompatibilities and the interactions between multiple incompatible siblings. To investigate the competitive interactions of closely related incompatible strains, we mutated Myxococcus xanthus DK1622, a predatory bacterium with complex social behavior. From 3392 random transposon mutations, we obtained 11 self-identification (SI) deficient mutants that formed unmerged colony boundaries with the ancestral strain. The mutations were at nine loci with unknown functions and formed nine independent SI mutants. Compared with their ancestral strain, most of the SI mutants showed reduced growth, swarming and development abilities, but some remained unchanged from their monocultures. When pairwise mixed with their ancestral strain for co-cultivation, these mutants exhibited improved, reduced or unchanged competitive abilities compared with the ancestral strain. The sporulation efficiencies were affected by the DK1622 partner, ranging from almost complete inhibition to 360% stimulation. The differences in competitive growth between the SI mutants and DK1622 were highly correlated with the differences in their sporulation efficiencies. However, the competitive efficiencies of the mutants in mixture were inconsistent with their growth or sporulation abilities in monocultures. We propose that the colony-merger incompatibility in M. xanthus is associated with multiple independent genetic loci, and the incompatible strains hold competitive interaction abilities, which probably determine the complex relationships between multiple incompatible M. xanthus strains and their co-existence strategies.

Homospermidine Lipids: A Compound Class Specifically Formed during Fruiting Body Formation of Myxococcus xanthus DK1622.

The fascinating ability of myxobacteria to form multicellular spore filled fruiting bodies under starvation conditions was widely studied as a model for cooperative microbial behavior. The potential of a life cycle induced change of secondary metabolism, as a means to discover novel natural products, remains largely underexplored. We therefore studied the model organism Myxococcus xanthus DK1622 under submersed and solid cultivation conditions to find putatively life-cycle related compounds by applying statistical analysis on analytical data. Utilizing the advantageous characteristics of LC-MS, LC-MS/MS, and MALDI-MSI allowed the identification of compounds unambiguously associated with myxobacterial fruiting bodies. Our screening effort resulted in the purification and structure elucidation of a novel compound, the homospermidine lipid, from cultures that had undergone the fruiting process. A combination of molecular networking and targeted LC-MS/MS in conjunction with our in-house metabolomics database subsequently revealed alternative producers of the respective compound as well as a number of compounds belonging to the same structural class. Three further members of this compound class were isolated from an alternative producer and structurally elucidated by NMR. Insights into the biosynthesis of this novel compound class was gained by feeding of isotopically labeled substrates and in silico analysis.

Heterologous production of myxobacterial α-pyrone antibiotics in Myxococcus xanthus

Myxopyronins (MXN) and corallopyronins (COR) are structurally related α-pyrone antibiotics from myxobacteria that represent a highly promising compound class for the development of broad-spectrum antibacterial therapeutic agents. Their ability to inhibit RNA polymerase through interaction with the “switch region”, a novel target, distant from previously characterized RNA polymerase inhibitors (e.g. rifampicin), makes them particularly promising candidates for further research. To improve compound supply for further investigation of MXN, COR and novel derivatives of these antibacterial agents, establishment of an efficient and versatile microbial production platform for myxobacterial α-pyrone antibiotics is highly desirable. Here we describe design, construction and expression of a heterologous production and engineering platforms for MXN and COR to facilitate rational structure design and yield improvement approaches in the myxobacterial host strain Myxococcus xanthus DK1622. Optimization of the cultivation medium yielded significantly higher production titers of MXN A at around 41-fold increase and COR A at around 25-fold increase, compared to the standard CTT medium.

Myxococcus xanthus DK1622 Coordinates Expressions of the Duplicate groEL and Single groES Genes for Synergistic Functions of GroELs and GroES.

Chaperonin GroEL (Cpn60) requires cofactor GroES (Cpn10) for protein refolding in bacteria that possess single groEL and groES genes in a bicistronic groESL operon. Among 4,861 completely-sequenced prokaryotic genomes, 884 possess duplicate groEL genes and 770 possess groEL genes with no neighboring groES. It is unclear whether stand-alone groEL requires groES in order to function and, if required, how duplicate groEL genes and unequal groES genes balance their expressions. In Myxococcus xanthus DK1622, we determined that, while duplicate groELs were alternatively deletable, the single groES that clusters with groEL1 was essential for cell survival. Either GroEL1 or GroEL2 required interactions with GroES for in vitro and in vivo functions. Deletion of groEL1 or groEL2 resulted in decreased expressions of both groEL and groES; and ectopic complementation of groEL recovered not only the groEL but also groES expressions. The addition of an extra groES gene upstream groEL2 to form a bicistronic operon had almost no influence on groES expression and the cell survival rate, whereas over-expression of groES using a self-replicating plasmid simultaneously increased the groEL expressions. The results indicated that M. xanthus DK1622 cells coordinate expressions of the duplicate groEL and single groES genes for synergistic functions of GroELs and GroES. We proposed a potential regulation mechanism for the expression coordination.

Error-prone DnaE2 Balances the Genome Mutation Rates in Myxococcus xanthus DK1622.

dnaE is an alpha subunit of the tripartite protein complex of DNA polymerase III that is responsible for the replication of bacterial genome. The dnaE gene is often duplicated in many bacteria, and the duplicated dnaE gene was reported dispensable for cell survivals and error-prone in DNA replication in a mystery. In this study, we found that all sequenced myxobacterial genomes possessed two dnaE genes. The duplicate dnaE genes were both highly conserved but evolved divergently, suggesting their importance in myxobacteria. Using Myxococcus xanthus DK1622 as a model, we confirmed that dnaE1 (MXAN_5844) was essential for cell survival, while dnaE2 (MXAN_3982) was dispensable and encoded an error-prone enzyme for replication. The deletion of dnaE2 had small effects on cellular growth and social motility, but significantly decreased the development and sporulation abilities, which could be recovered by the complementation of dnaE2. The expression of dnaE1 was always greatly higher than that of dnaE2 in either the growth or developmental stage. However, overexpression of dnaE2 could not make dnaE1 deletable, probably due to their protein structural and functional divergences. The dnaE2 overexpression not only improved the growth, development and sporulation abilities, but also raised the genome mutation rate of M. xanthus. We argued that the low-expressed error-prone DnaE2 played as a balancer for the genome mutation rates, ensuring low mutation rates for cell adaptation in new environments but avoiding damages from high mutation rates to cells.

Prediction of Metal Ion Binding Site in Truncated Globin of Myxococcus xanthus DK1622 in Homologous Model

Globins are heme containing proteins with the capability to bind oxygen reversibly. All globins can be classified as M (myoglobin-like), S (sensor) and T (truncated) globins; among them, M and S globins have a typical 3/3 α-helical globin fold and T globins have a 2/2 α-helical fold. Till date, all the myxobacterial genomes available in NCBI data base harbor one or more genes for globins but none of the globins from this group of bacteria have been characterized as yet. In this study, in-silico analysis and homology modeling approach was exploited to explore the physiochemical properties and 3-D structure of trHbN (group I T-globin) of Myxococcus xanthusDK1622, a fruiting myxobacteria. After generating the 3-D model, assessment of the structure and stereo-chemical analysis was carried using different evaluation and validation tools.As homologs of the trHbN exist in dimeric as well as monomeric form, dimerization studies were performed and it was observed that dimeric form of the protein is more stable as compared to the monomer. Further, heme group was appended to the model structure of trHbN of M. xanthus by Patchdock web server and model-heme complex was further refined by Firedock.The 3-D model structure will enhance the understanding for functional analysis of experimentally derived crystal structure.

Inter-laboratory evolution of a model organism and its epistatic effects on mutagenesis screens.

In theory, a few naturally occurring evolutionary changes in the genome of a model organism may have little or no observable impact on its wild type phenotype, and yet still substantially impact the phenotypes of mutant strains through epistasis. To see if this is happening in a model organism, we obtained nine different laboratories’ wild type Myxococcus xanthus DK1622 “sublines” and sequenced each to determine if they had evolved after their physical separation. Under a common garden experiment, each subline satisfied the phenotypic prerequisites for wild type, but many differed to a significant degree in each of the four quantitative phenotypic traits we measured, with some sublines differing by several-fold. Genome resequencing identified 29 variants between the nine sublines, and eight had at least one unique variant within an Open Reading Frame (ORF). By disrupting the ORF MXAN7041 in two different sublines, we demonstrated substantial epistasis from these naturally occurring variants. The impact of such inter-laboratory wild type evolution is important to any genotype-to-phenotype study; an organism’s phenotype may be sensitive to small changes in genetic background, so that results from phenotypic screens and other related experiments might not agree with prior published results or the results from other laboratories.

Genetic engineering and heterologous expression of the disorazol biosynthetic gene cluster via Red/ET recombineering

Disorazol, a macrocyclic polykitide produced by the myxobacterium Sorangium cellulosum So ce12 and it is reported to have potential cytotoxic activity towards several cancer cell lines, including multi-drug resistant cells. The disorazol biosynthetic gene cluster (dis) from Sorangium cellulosum (So ce12) was identified by transposon mutagenesis and cloned in a bacterial artificial chromosome (BAC) library. The 58-kb dis core gene cluster was reconstituted from BACs via Red/ET recombineering and expressed in Myxococcus xanthus DK1622. For the first time ever, a myxobacterial trans-AT polyketide synthase has been expressed heterologously in this study. Expression in M. xanthus allowed us to optimize the yield of several biosynthetic products using promoter engineering. The insertion of an artificial synthetic promoter upstream of the disD gene encoding a discrete acyl transferase (AT), together with an oxidoreductase (Or), resulted in 7-fold increase in disorazol production. The successful reconstitution and expression of the genetic sequences encoding for these promising cytotoxic compounds will allow combinatorial biosynthesis to generate novel disorazol derivatives for further bioactivity evaluation.

A comprehensive insight into the lipid composition of Myxococcus xanthus by UPLC-ESI-MS

Analysis of whole cell lipid extracts of bacteria by means of ultra-performance (UP)LC-MS allows a comprehensive determination of the lipid molecular species present in the respective organism. The data allow conclusions on its metabolic potential as well as the creation of lipid profiles, which visualize the organism's response to changes in internal and external conditions. Herein, we describe: i) a fast reversed phase UPLC-ESI-MS method suitable for detection and determination of individual lipids from whole cell lipid extracts of all polarities ranging from monoacylglycerophosphoethanolamines to TGs; ii) the first overview of a wide range of lipid molecular species in vegetative Myxococcus xanthus DK1622 cells; iii) changes in their relative composition in selected mutants impaired in the biosynthesis of α-hydroxylated FAs, sphingolipids, and ether lipids; and iv) the first report of ceramide phosphoinositols in M. xanthus, a lipid species previously found only in eukaryotes.

The groEL2 gene, but not groEL1, is required for biosynthesis of the secondary metabolite myxovirescin in Myxococcus xanthus DK1622

Myxococcus xanthus DK1622 possesses two copies of the groEL gene: groEL1, which participates in development, and groEL2, which is involved in the predatory ability of cells. In this study, we determined that the groEL2 gene is required for the biosynthesis of the secondary metabolite myxovirescin (TA), which plays essential roles in predation. The groEL2-knockout mutant strain was defective in producing a zone of inhibition and displayed decreased killing ability against Escherichia coli, while the groEL1-knockout mutant strain exhibited little difference from the wild-type strain DK1622. HPLC revealed that deletion of the groEL2 gene blocked the production of TA, which was present in the groEL1-knockout mutant. The addition of exogenous TA rescued the inhibition and killing abilities of the groEL2-knockout mutant against E. coli. Analysis of GroEL domain-swapping mutants indicated that the C-terminal equatorial domain of GroEL2 was essential for TA production, while the N-terminal equatorial or apical domains of GroEL2 were not sufficient to rescue TA production of the groEL2 knockout.

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.

Mechanisms Involved in the Functional Divergence of Duplicated GroEL Chaperonins in Myxococcus xanthus DK1622

The gene encoding the GroEL chaperonin is duplicated in nearly 30% of bacterial genomes; and although duplicated groEL genes have been comprehensively determined to have distinct physiological functions in different species, the mechanisms involved have not been characterized to date. Myxococcus xanthus DK1622 has two copies of the groEL gene, each of which can be deleted without affecting cell viability; however, the deletion of either gene does result in distinct defects in the cellular heat-shock response, predation, and development. In this study, we show that, from the expression levels of different groELs, the distinct functions of groEL1 and groEL2 in predation and development are probably the result of the substrate selectivity of the paralogous GroEL chaperonins, whereas the lethal effect of heat shock due to the deletion of groEL1 is caused by a decrease in the total groEL expression level. Following a bioinformatics analysis of the composition characteristics of GroELs from different bacteria, we performed region-swapping assays in M. xanthus, demonstrating that the differences in the apical and the C-terminal equatorial regions determine the substrate specificity of the two GroELs. Site-directed mutagenesis experiments indicated that the GGM repeat sequence at the C-terminus of GroEL1 plays an important role in functional divergence. Divergent functions of duplicated GroELs, which have similar patterns of variation in different bacterial species, have thus evolved mainly via alteration of the apical and the C-terminal equatorial regions. We identified the specific substrates of strain DK1622's GroEL1 and GroEL2 using immunoprecipitation and mass spectrometry techniques. Although 68 proteins bound to both GroEL1 and GroEL2, 83 and 46 proteins bound exclusively to GroEL1 or GroEL2, respectively. The GroEL-specific substrates exhibited distinct molecular sizes and secondary structures, providing an encouraging indication for GroEL evolution for functional divergence.

Identification and Localization of Myxococcus xanthus Porins and Lipoproteins

Myxococcus xanthus DK1622 contains inner (IM) and outer membranes (OM) separated by a peptidoglycan layer. Integral membrane, β-barrel proteins are found exclusively in the OM where they form pores allowing the passage of nutrients, waste products and signals. One porin, Oar, is required for intercellular communication of the C-signal. An oar mutant produces CsgA but is unable to ripple or stimulate csgA mutants to develop suggesting that it is the channel for C-signaling. Six prediction programs were evaluated for their ability to identify β-barrel proteins. No program was reliable unless the predicted proteins were first parsed using Signal P, Lipo P and TMHMM, after which TMBETA-SVM and TMBETADISC-RBF identified β-barrel proteins most accurately. 228 β-barrel proteins were predicted from among 7331 protein coding regions, representing 3.1% of total genes. Sucrose density gradients were used to separate vegetative cell IM and OM fractions, and LC-MS/MS of OM proteins identified 54 β-barrel proteins. Another class of membrane proteins, the lipoproteins, are anchored in the membrane via a lipid moiety at the N-terminus. 44 OM proteins identified by LC-MS/MS were predicted lipoproteins. Lipoproteins are distributed between the IM, OM and ECM according to an N-terminal sorting sequence that varies among species. Sequence analysis revealed conservation of alanine at the +7 position of mature ECM lipoproteins, lysine at the +2 position of IM lipoproteins, and no noticable conservation within the OM lipoproteins. Site directed mutagenesis and immuno transmission electron microscopy showed that alanine at the +7 position is essential for sorting of the lipoprotein FibA into the ECM. FibA appears at normal levels in the ECM even when a +2 lysine is added to the signal sequence. These results suggest that ECM proteins have a unique method of secretion. It is now possible to target lipoproteins to specific IM, OM and ECM locations by manipulating the amino acid sequence near the +1 cysteine processing site.

Evidence that a chaperone–usher-like pathway of Myxococcus xanthus functions in spore coat formation

Many bacteria use the chaperone-usher (CU) secretion pathway to assemble on their surfaces typical or atypical fimbrial organelles. Four consecutive genes of Myxococcus xanthus DK1622, MXAN3885-3882, were predicted to constitute an operon encoding a CU-like system involved in the assembly of the spore coat; however, experimental evidence supporting this hypothesis was lacking. In this study, co-transcription of MXAN3885-3883 was verified, and we found that this operon was expressed 12-15 h after initiation of M. xanthus development under conditions of stringent starvation. The MXAN3885 protein, which is highly homologous to, but expressed earlier than, the spore coat protein U of another M. xanthus strain, DZF1, was present mainly on the outer surface of myxospores. Inactivation of MXAN3883, encoding a putative outer membrane usher, inhibited assembly of MXAN3885 protein on spore surfaces and caused certain morphological alterations in the spore coat. Hence, the CU-like pathway in M. xanthus indeed functions in spore coat biogenesis. Based on chaperone amino acid sequence comparisons, our analysis suggests that the structural basis of the M. xanthus CU-like pathway for spore coat assembly may be different from that of most surface structures assembled by classical CU systems.

DKxanthene Biosynthesis—Understanding the Basis for Diversity-Oriented Synthesis in Myxobacterial Secondary Metabolism

The DKxanthenes are a family of yellow pigments which play a critical role in myxobacterial development. Thirteen unique structures from Myxococcus xanthus DK1622 differ in the length of their characteristic polyene functionality, as well as the extent of methyl branching. We aimed to understand the mechanistic basis for this "molecular promiscuity" by analyzing the gene cluster in DK1622, and comparing it to the DKxanthene biosynthetic locus in a second myxobacterium, Stigmatella aurantiaca DW4/3-1, which produces a more limited range of compounds. While the core biosynthetic machinery is highly conserved, M. xanthus contains a putative asparagine hydroxylase function which is not present in S. aurantiaca. This observation accounts, in part, for the significantly larger metabolite family in M. xanthus. Detailed analysis of the encoded hybrid polyketide synthase (PKS)-nonribosomal peptide synthetase (NRPS) assembly line provides direct evidence for the mechanism underlying the variable polyene length and the observed pattern of methyl functionalities.

Two Functionally Redundant Sfp‐Type 4′‐Phosphopantetheinyl Transferases Differentially Activate Biosynthetic Pathways in Myxococcus xanthus

A liberal alliance. Two Sfp-type 4′-phosphopantetheinyl transferases (PPTases, MxPpt1 and MxPpt2) are encoded in the Myxococcus xanthus DK1622 genome. Disruption or over-expression led to significant changes in secondary metabolism, but production of known compounds was not abolished. Both PPTases thus apparently differ in their specificity for biosynthetic pathways by employing carrier proteins from polyketide synthases and nonribosomal peptide synthetases.