Molecular insights intoVibrio cholerae’s intra-amoebal host-pathogen interactions

Abstract

Vibrio cholerae, which causes the diarrheal disease cholera, is a species of bacteria commonly found in aquatic habitats. Within such environments, the bacterium must defend itself against predatory protozoan grazers. Amoebae are prominent grazers, with Acanthamoeba castellanii being one of the best-studied aquatic amoebae. We previously showed that V. cholerae resists digestion by A. castellanii and establishes a replication niche within the host’s osmoregulatory organelle. In this study, we deciphered the molecular mechanisms involved in the maintenance of V. cholerae’s intra-amoebal replication niche and its ultimate escape from the succumbed host. We demonstrated that minor virulence features important for disease in mammals, such as extracellular enzymes and flagellum-based motility, play a key role role in the replication and transmission of V. cholerae in its aqueous environment. This work, therefore, describes new mechanisms that provide the pathogen with a fitness advantage in its primary habitat, which may have contributed to the emergence of these minor virulence factors in the species V. cholerae.

Ecological implications of gene regulation by TfoX and TfoY among diverse Vibrio species

“…The T6SS of pandemic V. cholerae is silent under standard laboratory conditions (Pukatzki et al ., ). In contrast to pandemic strains, the O37 serogroup strains V52 and ATCC25872 are toxigenic but nonpandemic and their T6SS is constitutively activated, as is the case for most environmental isolates (Pukatzki et al ., ; Unterweger et al ., ; Bernardy et al ., ; Van der Henst et al ., ). To explain the differences in T6SS activity and to provide insight into the T6SS's biological functions, it is, therefore, important to understand the underlying regulatory pathways in pandemic V. cholerae strains.…”

Interbacterial competition and anti-predatory behavior of environmentalVibrio choleraestrains

“…cholerae exerted a tight regulation over this toxin and thereby successfully infected the amoebae's contractile vacuole, constitutive hemolysin activity by the environmental isolates killed the host prematurely, preventing the formation of this replication niche (Van der Henst et al, 2018). We speculated that hemolysin activity could also be involved in the resistance against D. discoideum grazing that we observed for the environmental strains from clades C and D. To follow up on this hypothesis, we first tested all environmental WT strains for hemolysis on blood agar plates.…”

“…Notably, V. cholerae's T6SS was initially discovered due to its anti-eukaryotic activity that allowed the non-pandemic V. cholerae strain V52 to avoid predation by D. discoideum (Pukatzki et al, 2006). Indeed, previous studies had indicated that, in contrast to the 7 th pandemic strains, non-pandemic toxigenic V. cholerae (such as the two O37 serogroup strains V52 and ATCC25872; Pukatzki et al, 2006;Basler et al, 2012;Van der Henst et al, 2018) as well as environmental isolates (Unterweger et al, 2012;Bernardy et al, 2016;Crisan and Hammer, 2020) maintain constitutive T6SS activity. This is in contrast to the silenced T6SS of pandemic strains, which are primarily induced by chitin or low c-di-GMP levels, concomitantly with natural competence and the production of extracellular enzymes, respectively (Borgeaud et al, 2015;Watve et al, 2015;Veening and Blokesch, 2017).…”

“…Transformants were selected on kanamycincontaining agar plates and the lost rifampicin resistance was scored based on replica plating on plates +/-rifampicin using a velvet cloth. A second round of natural transformation followed to restore the lacZ gene by adding a WT lacZ PCR fragment to chitin-grown cells followed by a counter selection of the pheS* allele on 4-chloro-phenylalanine (20mM)containing agar plates as previously described (Van der Henst et al, 2018). To confirm the restoration of native rpoB, genomic DNA of A1552 Rif S was isolated and the PCR-amplified rpoB gene was Sanger-sequenced.…”

“…HlyA is considered a minor virulence factor as it contributes to toxicity in the context of intestinal infections (Ichinose et al, 1987;Olivier et al, 2007). We previously showed that the proper timing of HlyA activity is a prerequisite for pandemic V. cholerae to establish a replication niche within the aquatic -7-amoeba Acanthamoeba castellanii, while constitutive activity kills this host prematurely (Van der Henst et al, 2018).…”