The Agr communication system provides a benefit to the populations of Listeria monocytogenes in soil

Abstract

In this study, we investigated whether the Agr communication system of the pathogenic bacterium Listeria monocytogenes was involved in adaptation and competitiveness in soil. Alteration of the ability to communicate, either by deletion of the gene coding the response regulator AgrA (response-negative mutant) or the signal pro-peptide AgrD (signal-negative mutant), did not affect population dynamics in soil that had been sterilized but survival was altered in biotic soil suggesting that the Agr system of L. monocytogenes was involved to face the complex soil biotic environment. This was confirmed by a set of co-incubation experiments. The fitness of the response-negative mutant was lower either in the presence or absence of the parental strain but the fitness of the signal-negative mutant depended on the strain with which it was co-incubated. The survival of the signal-negative mutant was higher when co-cultured with the parental strain than when co-cultured with the response-negative mutant. These results showed that the ability to respond to Agr communication provided a benefit to listerial cells to compete. These results might also indicate that in soil, the Agr system controls private goods rather than public goods.

Keywords: Agr system; Listeria monocytogenes; biotic interaction; cell communication; competitiveness; fitness; soil.

Figure 1

Growth kinetics of L. monocytogenes (◼) parental strain, (⚫) signal- and (○) response-negative mutants in sterilized soil microcosms. Error bars represent the standard deviation from three replicate samples value.

Figure 2

L. monocytogenes (◼) parental strain, (⚫) signal- and (○) response-negative mutants survival in biotic soil microcosms. Error bars represent the standard deviation from three replicate samples value.

Figure 3

Dynamics of (A) the parental strain, (B) the response-negative mutant and (C) the signal-negative mutant populations in sterilized soil microcosms. (♦) Single culture, () co-culture with the parental strain, () co-culture with the response-negative mutant, () co-culture with the signal-negative mutant. Error bars represent the standard deviation from three replicate samples value.

Figure 4

Dynamics of (A) the parental strain, (B) the response-negative mutant and (C) the signal-negative mutant populations in biotic soil microcosms. (♦) Single culture, () co-culture with the parental strain, () co-culture with the response-negative mutant, () co-culture with the signal-negative mutant. Error bars represent the standard deviation from three replicate samples value.