Bacterial pathogens dynamic during multi-species infections
Abstract
Soft rot Pectobacteriacea (SRP) gathers more than 30 bacterial species that collectively
rot a wide range of plants by producing and secreting a large set of plant cell wall degrading
enzymes (PCWDEs).Worldwide potato field surveys identified 15 different SRP
species on symptomatic plants and tubers. The abundance of each species observed during
outbreaks varies over space and time and the mechanisms driving species shift during
outbreak are unknown. Furthermore, multi-species infections are frequently observed
and the dynamics of these coinfections are not well understood.To understand the dynamics
of coinfections, we set up 16 different synthetic communities of 6 SRP strains to
mimic coinfections. The bacteria present in each tested community were representative
of 2 different species, with 3 strains per species. These communities were inoculated
in potato tubers or on synthetic media and their outcome was followed by amplification
and Illumina sequencing of the discriminatory housekeeping gene gapA. We also
compared disease incidence and bacterial multiplication in potato tubers during mixedspecies
infection and single-species infection. A species that was unable to induce disease
in potato was efficiently maintained and eventually became dominant in some of
the communities tested, indicating that cheating can shape dominant species.Modeling
indicates that the cost of PCWDEs production and secretion, the rate of potato degradation
and the diffusion rate of degraded substrate could favor the cheater species. Interaction
outcomes differed between potato tuber and synthetic medium, highlighting
the driving effect of environmental conditions, with higher antagonistic interactions observed
in potato tubers. Antagonistic interactions were strain specific and not species
specific. Toxicity interference was also observed within some communities, allowing the
maintenance of strains otherwise sensitive to toxic compounds. Overall, the results indicate
that intraspecific competition, cooperation through trophic interaction and toxicity
interference contribute to the maintenance of SRP diversity. The implications of these
processes for epidemiological surveillance are discussed.
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