Cyanide Production by Chromobacterium piscinae Shields It from Bdellovibrio bacteriovorus HD100 Predation

Abstract

Predation of Chromobacterium piscinae by Bdellovibrio bacteriovorus HD100 was inhibited in dilute nutrient broth (DNB) but not in HEPES. Experiments showed that the effector responsible was present in the medium, as cell-free supernatants retained the ability to inhibit predation, and that the effector was not toxic to B. bacteriovorus. Violacein, a bisindole secondary metabolite produced by C. piscinae, was not responsible. Further characterization of C. piscinae found that this species produces sufficient concentrations of cyanide (202 µM) when grown in DNB to inhibit the predatory activity of B. bacteriovorus, but that in HEPES, the cyanide concentrations were negligible (19 µM). The antagonistic role of cyanide was further confirmed, as the addition of hydroxocobalamin, which chelates cyanide, allowed predation to proceed. The activity of cyanide against B. bacteriovorus was found to be twofold, depending on the life cycle stage of this predator. For the attack-phase predatory cells, cyanide caused the cells to lose motility and tumble, while for intraperiplasmic predators, development and lysis of the prey cell were halted. These findings suggest that cyanogenesis in nature may be employed by the bacterial strains that produce this compound to prevent and reduce their predation by B. bacteriovorus.

Viscosity has dichotomous effects on Bdellovibrio bacteriovorus HD100 predation

“…Enhanced motilities with Leptospira interrogans (Berg and Turner, 1979) and Pseudomonas viscosa, Bacillus brevis or E. coli (Shoesmith, 1960) were also reported in other studies with methylcellulose and carrageenan. In the latter publication, the speed of E. 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, 2006;Dwidar et al, 2015;Im et al, 2017;Mun et al, 2017), 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.…”

“…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.…”

“…Several studies reported on a variety of environmental and biological factors that impact predation (Dwidar et al, 2015;Im et al, 2017;Mun et al, 2017;Garcia et al, 2018). More recently, Duncan et al (2018) published an interesting article discussing B. bacteriovorus HD100's ability to predate on the highly motile Vibrio cholera, with the predator apparently being dragged along as the prey continued to swim after initial attachment (Duncan et al, 2018).…”

“…They found indole significantly hindered the predator's motility during the attack-phase and its development within the bdelloplast, with 2 mM indole effectively bringing predation to a halt without being toxic towards the predator. Similarly, cyanogenic bacteria prevent their own predation when a small amount of amino acids is provided (Mun et al, 2017). They achieve this resistance by producing cyanide, a poison that inhibits the electron transport system within B. bacteriovorus, a strict aerobe.…”