Bdellovibrio bacteriovorus: a potential ‘living antibiotic’ to control bacterial pathogens

Figures & data

Figure 1. Schematic representation of the life cycle of B. bacteriovorus. Starting clockwise from top left of the image, the predator approaches and binds to the outer surface of its prey. The flagellum is lost and a pore is created. The predator penetrates and settles in the periplasmic space of its host. Subsequently, the pore is sealed and the predator starts consuming the intracellular components of its prey. A septation step follows, culminating in lysis of the host cell and the release of fresh B. bacteriovorus progeny. The new-born predators then start a new predation cycle either through the Host-Dependent cycle or can revert in the Host-Independent state until a suitable prey is encountered.

Figure 2. TEM images of various stages of predation. The prey in the images is an Enterobacter roggenkampii isolate. Images I, II and III show B. bacteriovorus HD100 (indicated with arrows) attached to the outer surface of a prey cell or in its immediate surroundings. Image IV shows a late stage of predation where the new-born predators are in the bdelloplast, prior to its disruption (our unpublished data).

Table 1. Overview of bacteria known to display predatory lifestyles.

Nomenclature genus/species	Predation strategy	Prey disruption mechanism	Reference
Bdellovibrio bacterivorous	Endobiotic	Lytic enzyme	(Stolp and Starr 1963)
Vampirococcus	Epibiotic	Lytic enzymes	(Guerrero et al. 1986)
Ensifer adhaerens	Epibiotic	Lytic enzymes	(Casida 1982)
Micavibrio aeruginosavorus	Epibiotic	Lytic enzymes	(Lambina et al. 1983)
Bdellovibrio exovorus	Epibiotic	Lytic enzymes	(Koval et al. 2013)
Bradymonabacteria	Epibiotic	Antimicrobials Contact-dependent	(Mu et al. 2020)
Cytophaga	Epibiotic	Lytic enzymes	(Imai et al. 1993)
Flavobacterium	Epibiotic	Lytic enzymes	(Bernardet et al. 1996)
Fibrella aestuarina	Epibiotic	Lytic enzymes	(Filippini, Svercel, et al. 2011)
Fibrisoma limi	Epibiotic	Lytic enzymes	(Filippini, Kaech, et al. 2011)
Agromyces ramosus	Epibiotic	Lytic enzymes	(Gledhill and Casida 1969)
Lysobacter	Epibiotic	Lytic enzymes	(Christensen and Cook 1978)
Cupriavidus necator	Epibiotic	Far-reaching secondary metabolites	(Makkar and Casida 1987)
Stenotrophomonas maltophilia	Epibiotic	Far-reaching secondary metabolites	(Hugh and Leifson 1963)
Saprospira	Group attack	Secretion of substances that capture and lyse the prey Gliding motility	(Ashton and Robarts 1987)
Streptomyces	Group attack	Secondary metabolites Antimicrobials	(Kumbhar et al. 2014)
Myxobacteria	Group attack	Cooperative predation Secondary metabolites Gliding motility	(Hart and Zahler 1966)
Herpetosiphon	Group attack	Cooperative predation	(Quinn and Skerman 1980)

General overview of bacteria with known predatory lifestyles. The term epibiotic refers to a predation performed by the predator while remaining attached to the outer surface of its prey. With endobiotic predation, the predator physically enters into the prey cell. Group attack also referred to as wolf pack predation, involves a certain quorum of predators working in synergy to perform the predation.

Table 2. Overview of in vivo studies that used B. bacteriovorus as a biocontrol agent against pathogens.

In vivo model	Pathogen	Predator	Infection method	Infection days	Detection method	Outcome	Reference
Gallus gallus domesticus, Hy-line	Salmonella enteritidis P125109	B. bacteriovorus HD100 B. bacteriovorus HI ΔpilA	Oral gavage	28	Prey CFU of caecal region of intestinal tract	Reduction of prey CFU count Predator could survive the GI tract Safety of ingestion	(Atterbury et al. 2011)
Rattus norvegicus	Various oral pathogens*	B. bacteriovorus HD100	3 topical administrations of predator to rat gingivas	14	qPCR	Protective effect of bone and connective tissue	(Silva et al. 2019)
Penaeus vannamei	Various Vibrio** species	Unspecified	Predator added to the media of the shrimps	7	Plaques forming units (PFU) after predation	Reduced mortality of host	(Cao et al. 2015)
Mus musculus, SKH-1 and BALB/c	Yersinia pestis CO92	B. bacteriovorus HD100	Single dose of pathogen Predator administered every 24 h	4	Prey CFU counting Mouse whole-body imaging mCherry labelling of predator	Protection from lethal dose Reservoir of predator in adipose tissue of mouse	(Findlay et al. 2019)
Oryctolagus cuniculus, New Zealand White (NZW)		B. bacteriovorus HD100 B. bacteriovorus 109 J M. aeruginosavorus ARL-13	Corneal epithelium Multiple administration	11	Fluorescein to detect inflammation or toxicity	No toxicity detected on the rabbit ocular surface	(Romanowski et al. 2016)
Danio rerio, Zebrafish larvae	Shigella flexneri M90T	B. bacteriovorus HD100	Co-infection of prey and predator	3	mCherry labelling of predator GFP labelling of prey	Synergistic effect of predator and host leukocytes	(Willis et al. 2016)
Mus musculus, C57BL/6		B. bacteriovorus HD100 B. bacteriovorus 109 J M. aeruginosavorus ARL-13	Infection performed with only predators	2	RT-qPCR ELISA	Safety of intravenous and respiratory infections of the predators	(Shatzkes et al. 2015)

*Actinomyces and Streptococcus-like species, Campylobacter gracilis, Capnocytophaga sputigena, Eikenella corrodens, Eubacterium nodatum, Fusobacterium nucleatum, Fusobacterium polymorphum, Peptostreptococcus micros, Prevotella intermedia, Veillonella parvula.

**Vibrio alginolyticus BYK00019, V alginolyticus BYK0834, Vibrio anguillarum BYK0638, V. cholerae GYL, V. cholerae LD081008B-1, Vibrio harveyi BYK00034, Vibrio harveyi ZL0022, Vibrio parahaemolyticus ZL0025, V. parahaemolyticus ZL0040, Vibrio vulnificus BYK000965,

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