The opposite effects of stringent response on phage infection of Pseudomonas putida

TL;DR

This study shows that the stringent response in Pseudomonas putida has mixed effects on phage infections, sometimes helping and sometimes hindering them.

Contribution

The paper reveals the diverse and opposing effects of (p)ppGpp on phage infection in Pseudomonas putida.

Findings

P. putida cells lacking (p)ppGpp show impaired membrane integrity in stationary phase.

Approximately half of the tested phages infect (p)ppGpp0 cells more efficiently, while the other half show reduced infection.

Phage infection differences are due to downstream steps like latent period or unproductive infection, not adsorption rates.

Abstract

Guanosine tetra- and pentaphosphate ((p)ppGpp) are one of the key players in the stress response of bacteria. Accumulation of these alarmones activates the stringent response, usually triggered by different nutritional stresses. For Pseudomonas putida, there is only limited data available on the importance of the stringent response in stress situations. Also, in recent years, different specific phage defence systems have received much attention, but little is known about the involvement of stringent response in phage infection. Here, we show that P. putida PaW85 (p)ppGpp0 is prototrophic and tolerates chemical stress well. However, in the stationary phase P. putida cells deprived of (p)ppGpp have impaired membrane integrity. In addition, we conducted a large-scale screening of stringent response effects on phage infections using the CEPEST phage collection. We tested 67 phages of 22 different species and revealed that the lack of (p)ppGpp has opposing effects on phage infection with nearly half of the tested phages showing higher infection efficiency on the (p)ppGpp0 cells, whereas the other half shows reduced infection. We show that the differences in phage infection efficiency for phages Aura and Amme-3 are not caused by adsorption rate differences, but alterations in downstream steps of the infection cycle—prolonged latent period in the absence of (p)ppGpp or unproductive infection in the presence of (p)ppGpp. Altogether, results indicate that the role of stringent response in phage infection is highly diverse, and over half of the times the presence of (p)ppGpp facilitates phage infections rather than protects the cells.

We demonstrate that some phages are inhibited by stringent response while others require it for efficient infections of Pseudomonas putida, a biotechnologically important model organism.

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