Cross-Species GacA-Controlled Induction of Antibiosis in Pseudomonads

Abstract

Signal extracts prepared from culture supernatants of Pseudomonas fluorescens CHA0 and Pseudomonas aeruginosa PAO stimulated GacA-dependent expression of small RNAs and hence of antibiotic compounds in both hosts. Pseudomonas corrugata LMG2172 and P. fluorescens SBW25 also produced signal molecules stimulating GacA-controlled antibiotic synthesis in strain CHA0, illustrating a novel, N-acyl-homoserine lactoneindependent type of interspecies communication.

Evolutionary history predicts the stability of cooperation in microbial communities

“…The gac/rsm QS pathway is highly conserved among Pseudomonas spp. 25 , and phylogenetically distant species engage in cooperation due to an overlap in QS signals 17 positively correlates with phylogenetic distance 24 . In an ideal scenario, distant species cooperate making a common resource available.…”

“…We counted colonies lacking exoproteases and tryptophan dioxygenase as signal-blind defectors 27 . In order to further test if these mutants are signal blind, we randomly picked 20 protease-deficient isolates and attempted to grow them in QSM medium with or without an organic extract from wild-type cultures (containing QS signals) as described elsewhere 17 .…”

“…Most studies use the Hamiltonian kin selection framework 15 predicting that altruism becomes evolutionary stable as relatedness augments. In a multispecies system, this concept can be extended to evolutionary history: because of their common ancestry, different species may share compatible kin recognition mechanisms and perceive each other as partner, although differing at the level of the cooperative locus 16,17 .…”

“…Albumin first has to be degraded by extracellular proteases, which function as a QS-regulated public good in Pseudomonas 25 . Fluorescent pseudomonads produce extracellular proteases under the control of the gac-rsm QS system and may respond to their own as well as other species' QS signals 17,25 . We monitor the apparition of spontaneous protease-deficient defectors in communities of varying phylogenetic history and richness.…”

“…Diversity does not impede cooperation per se 20 , but makes it difficult to predict using the Hamiltonian framework. In multispecies communities, cross-talk between unrelated species may result in cooperative behaviour 17 . Further, antagonistic interactions, as caused by the production of bacteriocins or antibiotics, may harm a broad range of competitors 21 , independent of their cooperativeness or shared evolutionary history with the emitter strain 22 .…”