Bacterial endophytes are widely studied for their ability to produce antimicrobial compounds. Rheinheimera sp. strain EpRS3 isolated from the rhizospheric soil of the medicinal plant Echinacea purpurea, is known for its ability to produce antimicrobial compounds inhibiting the growth of other bacterial species, both environmental and opportunistic human pathogens. In vivo experiments demonstrated a killing effect of EpRS3 strain against the ciliated protist Euplotes aediculatus strain EASCc1, which is known by FISH and TEM analyses to harbour in the cytoplasm the obligate bacterial endosymbiont Polynucleobacter necessarius (Betaproteobacteria) and the Francisella-related endosymbiont “Candidatus Nebulobacter yamunensis.” (Gammaproteobacteria). When the ciliate is treated with supernatant of Rheinheimera sp. culture (liquid broth free of bacteria), the number of living eukaryotic cells decreases with respect to control cells. TEM analysis, aimed at revealing the induced ultrastructural ciliate cell damages, showed that inside these ciliates P. necessarius endosymbionts went into degradation and vacuolization. When the ciliate culture is inoculated with bacteria plus medium, the number of living eukaryotic cells decreases until disappearance within six hours, and many damaged or highly degraded ciliate mitochondria and a decrement in number of P. necessarius endosymbionts are recorded. Additionally, in these ciliates both TEM observation and FISH experiments performed using a specific molecular probe disclosed the presence of Rheinheimera sp. both inside phagosomes and free in the cytoplasm, suggesting that it is somehow capable to escape from food vacuoles avoiding ciliate digestion. The obtained results suggest that Rheinheimera sp. EpRS3 produces and releases in liquid culture one or more compounds affecting E. aediculatus survival. Analyses are now focused on clarifying the molecular mechanisms behind the observed Rheinheimera’s killing effect.

Killing effect of Rheinheimera sp. Eprs3 (Gammaproteobacteria) against Euplotes aediculatus (Ciliophora, Spirotrichea): discovering the ecological role of antimicrobial compounds from environmental bacterial strains

LETIZIA MODEO
Primo
Writing – Original Draft Preparation
;
CAROLINA CHIELLINI
Secondo
Writing – Original Draft Preparation
;
CHIARA PASQUALETTI
Writing – Original Draft Preparation
;
OLIVIA LANZONI
Penultimo
Writing – Review & Editing
;
GIULIO PETRONI
Ultimo
Funding Acquisition
2018-01-01

Abstract

Bacterial endophytes are widely studied for their ability to produce antimicrobial compounds. Rheinheimera sp. strain EpRS3 isolated from the rhizospheric soil of the medicinal plant Echinacea purpurea, is known for its ability to produce antimicrobial compounds inhibiting the growth of other bacterial species, both environmental and opportunistic human pathogens. In vivo experiments demonstrated a killing effect of EpRS3 strain against the ciliated protist Euplotes aediculatus strain EASCc1, which is known by FISH and TEM analyses to harbour in the cytoplasm the obligate bacterial endosymbiont Polynucleobacter necessarius (Betaproteobacteria) and the Francisella-related endosymbiont “Candidatus Nebulobacter yamunensis.” (Gammaproteobacteria). When the ciliate is treated with supernatant of Rheinheimera sp. culture (liquid broth free of bacteria), the number of living eukaryotic cells decreases with respect to control cells. TEM analysis, aimed at revealing the induced ultrastructural ciliate cell damages, showed that inside these ciliates P. necessarius endosymbionts went into degradation and vacuolization. When the ciliate culture is inoculated with bacteria plus medium, the number of living eukaryotic cells decreases until disappearance within six hours, and many damaged or highly degraded ciliate mitochondria and a decrement in number of P. necessarius endosymbionts are recorded. Additionally, in these ciliates both TEM observation and FISH experiments performed using a specific molecular probe disclosed the presence of Rheinheimera sp. both inside phagosomes and free in the cytoplasm, suggesting that it is somehow capable to escape from food vacuoles avoiding ciliate digestion. The obtained results suggest that Rheinheimera sp. EpRS3 produces and releases in liquid culture one or more compounds affecting E. aediculatus survival. Analyses are now focused on clarifying the molecular mechanisms behind the observed Rheinheimera’s killing effect.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/943879
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