The Myxobacterium Myxococcus xanthus Can Sense and Respond to the Quorum Signals Secreted by Potential Prey Organisms.

David E Whitworth,Daniel G Lloyd

doi:10.3389/fmicb.2017.00439

Abstract

The myxobacterium Myxococcus xanthus is a predatory member of the soil microfauna, able to consume bacteria (Gram-negative, Gram-positive), archaea, and fungi. Many potential prey of M. xanthus communicate amongst themselves using acyl homoserine lactones (AHLs) as quorum signals. M. xanthus cannot itself produce AHLs, but could potentially benefit by responding to exogenous AHLs produced during signaling between proximal prey. Four AHLs of different side chain length were tested and all found to delay sporulation of M. xanthus vegetative cells, and to stimulate germination of myxospores, increasing the proportion of predatory vegetative cells in the population. The predatory activity and expansion rates of M. xanthus colonies were also found to be stimulated by AHLs. Thermally inactivated AHLs had no effect on M. xanthus cells, and the response to AHLs depended (non-linearly) on the length of AHL side chain, suggesting that the effect of AHLs was mediated by specific signaling within M. xanthus, rather than being a consequence of the chemical or physical properties of AHLs. Therefore, it seems that the presence of xenic quorum signaling molecules enhances the predatory activity of M. xanthus. AHLs increase the proportion of the population capable of predation, and stimulate the motility and predatory activity of vegetative cells. We therefore propose that in the wild, M. xanthus uses AHLs as markers of nearby prey, potentially eavesdropping on the conversations between prey organisms.

Highlights

Our current understanding of the soil microbiome, and crosstalk therein, is limited by the complexity of the potential interactions between individual denizens (Hirsch and Mauchline, 2012)
To test for any effect of quorum signaling (QS) molecules on motility, colony expansion assays were performed in the presence and absence of four acyl homoserine lactones (AHLs) (C4-HSL, C6-HSL, C8-HSL, and C10-HSL)
The rate of swarm expansion was not significantly affected by the nutritional value of the medium (DCY, DCY/10 or TM), but the size of the stimulatory effect depended on the specific AHL being tested

Summary

Introduction

Our current understanding of the soil microbiome, and crosstalk therein, is limited by the complexity of the potential interactions between individual denizens (Hirsch and Mauchline, 2012). Myxobacterial Predation Responds to AHLs. Within the soil there are numerous species competing for nutrients and space, creating complex food webs which culminate in a small number of ‘apex’ style carbon sequesterers (Lueders et al, 2006). Within the soil there are numerous species competing for nutrients and space, creating complex food webs which culminate in a small number of ‘apex’ style carbon sequesterers (Lueders et al, 2006) Throughout such competitive ecosystems, individuals often seek to enhance their long term survival via mutual cooperation, which imposes a fitness cost on the individual, but increases the fitness of the population as a whole (Strassmann et al, 2011). In order to orchestrate population-wide behaviors such as biofilm formation, quorum signaling (QS) systems are often used by bacteria to regulate gene expression (Miller and Bassler, 2001). There have been numerous systems characterized, each producing and detecting highly specific quorum signals (Dong and Zhang, 2005; Waters and Bassler, 2005)

Methods

Results

Conclusion