Myxococcus xanthus Predation of Gram-Positive or Gram-Negative Bacteria Is Mediated by Different Bacteriolytic Mechanisms

Abstract

Myxococcus xanthus kills other species to use their biomass as energy source. Its predation mechanisms allow feeding on a broad spectrum of bacteria, but the identity of predation effectors and their mode of action remains largely unknown. We initially focused on the role of hydrolytic enzymes for prey killing and compared the activity of secreted M. xanthus proteins against four prey strains. 72 secreted proteins were identified by mass spectrometry, and among them a family 19 glycoside hydrolase that displayed bacteriolytic activity in vivo and in vitro. This enzyme, which we name LlpM (lectin/lysozyme-like protein of M. xanthus), was not essential for predation, indicating that additional secreted components are required to disintegrate prey. Furthermore, secreted proteins lysed only Gram-positive, but not Gram-negative species. We thus compared the killing of different preys by cell-associated mechanisms: Individual M. xanthus cells killed all four test strains in a cell-contact dependent manner, but were only able to disintegrate Gram-negative, not Gram-positive cell envelopes. Thus, our data indicate that M. xanthus uses different, multifactorial mechanisms for killing and degrading different preys. Besides secreted enzymes, cell-associated mechanisms that have not been characterized so far, appear to play a major role for prey killing. IMPORTANCE Predation is an important survival strategy of the widespread myxobacteria, but it remains poorly understood on the mechanistic level. Without a basic understanding of how prey cell killing and consumption is achieved, it also remains difficult to investigate the role of predation for the complex myxobacterial lifestyle, reciprocal predator-prey relationships or the impact of predation on complex bacterial soil communities. We study predation in the established model organism Myxococcus xanthus, aiming to dissect the molecular mechanisms of prey cell lysis. In this study, we addressed the role of secreted bacteriolytic proteins, as well as potential mechanistic differences in the predation of Gram-positive and Gram-negative bacteria. Our observation shows that secreted enzymes are sufficient for killing and degrading Gram-positive species, but that cell-associated mechanisms may play a major role for killing Gram-negative and Gram-positive prey on fast timescales.

The Predatory Myxobacterium Citreicoccus inhibens gen. nov. sp. nov. Showed Antifungal Activity and Bacteriolytic Property against Phytopathogens

“…The direct lysis of pathogenic cells by extracellular enzymes is another biocontrol mechanism against phytopathogens [57,58]. Myxobacteria are micropredators feeding on prey cells, which involves the lysis of prey cells with hydrolase cargo loaded by outermembrane vesicles [17,40].…”

Hidden paths to endless forms most wonderful: Ecology latently shapes evolution of multicellular development in predatory bacteria

“…CC-BY-NC-ND 4.0 International license made available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprint this version posted June 17, 2021. ; https://doi.org/10.1101/2021.06.17.448787 doi: bioRxiv preprint 4 myxobacteria kill and consume diverse microbes as prey (both prokaryotic and eukaryotic) by molecular mechanisms that remain to be well-characterized 39,40 . M. xanthus employs two mechanistically distinct (but pleiotropically connected) modes of motility to migrate in search of prey and other resources and to carry out aggregative multicellular development.…”

“…Among prokaryotes, predatory myxobacteria are probably the most recognized in this regard, especially the model species Myxococcus xanthus 37 , which is found in many soil habitats worldwide 38 . In the vegetative-growth phase of their multicellular life cycles, many myxobacteria kill and consume diverse microbes as prey (both prokaryotic and eukaryotic) by molecular mechanisms that remain to be well-characterized 39,40 . M. xanthus employs two mechanistically distinct (but pleiotropically connected) modes of motility to migrate in search of prey and other resources and to carry out aggregative multicellular development.…”

Differential response to prey quorum signals indicates predatory range of myxobacteria

“…In fact, the chemical ecology of predator-prey interactions between myxobacteria and prey remains underexplored (Findlay, 2016). The predatory capacity or prey range of myxobacteria cannot be directly correlated with phylogeny (Livingstone et al, 2017;Arend et al, 2020).…”

“…Presently, the best determinants for broadly assessing prey ranges are genetic features that might provide specific traits to overcome predation resistances of individual prey. For example, myxobacteria possessing the formaldehyde dismutase gene fdm demonstrated comparatively better predation of toxic formaldehyde secreting Pseudomonas aeruginosa a clinical pathogen observed to be somewhat recalcitrant to myxobacterial predation (Arend et al, 2020).…”