Indole negatively impacts predation by Bdellovibrio bacteriovorus and its release from the bdelloplast

Abstract

Bdellovibrio bacteriovorus is a predatory bacterium that attacks a wide range of Gram-negative bacterial pathogens and is proposed to be a potential living antibiotic. In this study, we evaluated the effects of indole, a bacterial signalling molecule commonly produced within the gut, on the predatory ability of B. bacteriovorus HD100. Indole significantly delayed predation on Escherichia coli MG1655 and Salmonella enterica KACC 11595 at physiological concentrations (0.25 to 1 mM) and completely inhibited predation when present at 2 mM. Microscopic analysis revealed that indole blocked the predator from attacking the prey. Furthermore, indole was not toxic to the predator but slowed down its motility. Microarray and reverse transcription quantitative polymerase chain reaction (RT-qPCR) analyses confirmed that as the gene group showing the greatest downregulation in the presence of indole was flagellar assembly genes. Indole also caused a wide spectrum changes in gene expression including general downregulation of genes involved in ribosome assembly. Furthermore, indole addition to the predatory culture after the entrance of B. bacteriovorus into the prey periplasm slowed down bdelloplast lysis. In conclusion, indole can have significant impacts on the predation efficiency, which should be taken into consideration especially if B. bacteriovorus is to be applied as a probiotic or living antibiotic.

Roles of Indole as an Interspecies and Interkingdom Signaling Molecule

“…For example, indole inhibits the attachment of the fungal pathogen Candida albicans to intestinal epithelial HT-29 cells [56] and reduces the production of the virulence factor staphyloxanthin in Staphylococcus aureus [57]; both of these studies demonstrated virulence reduction in a Caenorhabditis elegans model [56,57]. Indole also inhibits cyanobacterial blooms caused by the formation of periphyton biofilms [58], induces biofilm formation by rhizospheric Burkholderia unamae [59], and delays predation by Bdellovibrio bacteriovorus [60]. It would be interesting to determine whether indole affects the virulence of other pathogens as well as those of environmental bacteria.…”

Viscosity has dichotomous effects onBdellovibrio bacteriovorusHD100 predation

“…Several studies reported on a variety of environmental and biological factors that impact predation (Dwidar et al ., ; Im et al ., ; Mun et al ., ; Garcia et al ., ). More recently, Duncan et al .…”

“…coli increased by as much as 40% when the viscosity was 1.33 mPa s. Using 1% PEG here, we achieved a comparable increase (31%) in the average speed of B . bacteriovorus HD100, albeit at 5.4 mPa s. Based on the literature, the typical speed for this organism tends to fall between 20 and 50 μm s −1 (Lambert et al ., ; Dwidar et al ., ; Im et al ., ; Mun et al ., ), a range that includes the average measured here in HEPES‐salt, i.e., 47.5 μm s −1 . However, in 1% PEG, several of the cells had speeds that surpassed 120 μm s −1 while the maximum speed recorded was 132 μm s −1 (Fig.…”

“…Dwidar et al . () describes both the transcriptional responses as well as physical manifestations induced in B . bacteriovorus HD100 when exposed to physiological concentrations of this secondary metabolite.…”

Isolation of Indole Utilizing Bacteria Arthrobacter sp. and Alcaligenes sp. From Livestock Waste

“…Biochemical and molecular studies have shown that indole plays various roles in bacterial systems, for example, as an extracellular signal [1,3], for multicopy plasmid maintenance [4], cell division, biofilm formation [5], and acid and drug resistance [5][6][7][8]. In addition, indole also controls the virulence of several pathogenic bacteria [7] and it has multifaceted properties and applications in prokaryotic systems [9][10][11] as well as eukaryotic systems [12].…”