Predatory outer membrane vesicles (OMVs) secreted by myxobacteria fuse readily with the outer membranes of Gram-negative bacteria, introducing toxic cargo into their prey. Here we used a strain of the myxobacterium Myxococcus xanthus that produces fluorescent OMVs to assay the uptake of OMVs by a panel of Gram-negative bacteria. M. xanthus strains took up significantly less OMV material than the tested prey strains, suggesting that re-fusion of OMVs with producing organisms is somehow inhibited. The OMV killing activity against different prey correlated strongly with the predatory activity of myxobacterial cells, however, there was no correlation between OMV killing activity and their propensity to fuse with different prey. It has previously been proposed that M. xanthus GAPDH stimulates the predatory activity of OMVs by enhancing OMV fusion with prey cells. Therefore, we expressed and purified active fusion proteins of M. xanthus glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase (GAPDH and PGK; moonlighting enzymes with additional activities beyond their roles in glycolysis/gluconeogenesis) to investigate any involvement in OMV-mediated predation. Neither GAPDH nor PGK caused lysis of prey cells or enhanced OMV-mediated lysis of prey cells. However, both enzymes were found to inhibit the growth of Escherichia coli, even in the absence of OMVs. Our results suggest that fusion efficiency is not a determinant of prey killing, but instead resistance to the cargo of OMVs and co-secreted enzymes dictates whether organisms can be preyed upon by myxobacteria.
Myxobacteria are fascinating and complex microbes. They prey upon other members of the soil microbiome by secreting antimicrobial proteins and metabolites, and will undergo multicellular development if starved. The genome sequence of the model myxobacterium Myxococcus xanthus DK1622 was published in 2006 and 15 years later, 163 myxobacterial genome sequences have now been made public. This explosion in genomic data has enabled comparative genomics analyses to be performed across the taxon, providing important insights into myxobacterial gene conservation and evolution. The availability of myxobacterial genome sequences has allowed system-wide functional genomic investigations into entire classes of genes. It has also enabled post-genomic technologies to be applied to myxobacteria, including transcriptome analyses (microarrays and RNA-seq), proteome studies (gel-based and gel-free), investigations into protein–DNA interactions (ChIP-seq) and metabolism. Here, we review myxobacterial genome sequencing, and summarise the insights into myxobacterial biology that have emerged as a result. We also outline the application of functional genomics and post-genomic approaches in myxobacterial research, highlighting important findings to emerge from seminal studies. The review also provides a comprehensive guide to the genomic datasets available in mid-2021 for myxobacteria (including 24 genomes that we have sequenced and which are described here for the first time).
Myxobacteria produce a variety of bioactive secondary metabolites, and with a wealth of under-researched species they hold vast potential for undiscovered compounds. With the ever-increasing need for new antibiotics, the development of novel therapeutics is vitally important. Therefore, this study aimed to extract and elucidate antimicrobial metabolites from the following myxobacteria: Myxococcus xanthus CA010 and AB022; Corallococcus exiguus DSM14696T; Myxococcus stipitatus DSM14675T; Corallococcus aberystwythensis AB050AT. Metabolite mixtures were extracted in acetone from XAD-16 resin incubated in liquid cultures and analysed using GC-MS. Bioactivity was identified using a growth inhibition assay against a panel of clinically relevant prey species including Gram-positive and Gram-negative bacteria and a fungus. The growth of Klebsiella pneumoniae and Enterococcus faecalis was most affected by the metabolite mixtures and the mixtures from AB022 and AB050AT were effective against the most prey. GC-MS analysis revealed metabolites with roles in synthesis and degradation of amino acids and fatty acids, but also identified compounds A and B with a diketopiperazine (DKP) core. With previously confirmed bioactivity of compound A, it is suggested that these DKP compounds are contributing to the antimicrobial activity observed. Furthermore, many compounds could not be identified and so these unknowns present further potential for novel bioactive compounds.
Myxobacteria produce a variety of bioactive secondary metabolites, and with a wealth of under-researched species they hold vast potential for undiscovered compounds. With the ever-increasing need for new antibiotics, the development of novel therapeutics is vitally important. Therefore, this study aimed to extract and elucidate antimicrobial metabolites from the following myxobacteria: Myxococcus xanthus CA010 and AB022; Corallococcus exiguus DSM14696T; Myxococcus stipitatus DSM14675T; Corallococcus aberystwythensis AB050AT. Metabolite mixtures were extracted in acetone from XAD-16 resin incubated in liquid cultures and analysed using GC-MS. Bioactivity was identified using a growth inhibition assay against a panel of clinically relevant prey species including Gram-positive and Gram-negative bacteria and a fungus. The growth of Klebsiella pneumoniae and Enterococcus faecalis was most affected by the metabolite mixtures and the mixtures from AB022 and AB050AT were effective against the most prey. GC-MS analysis revealed metabolites with roles in synthesis and degradation of amino acids and fatty acids, but also identified compounds A and B with a diketopiperazine (DKP) core. With previously confirmed bioactivity of compound A, it is suggested that these DKP compounds are contributing to the antimicrobial activity observed. Furthermore, many compounds could not be identified and so these unknowns present further potential for novel bioactive compounds.
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