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Soft rot pectobacteria (SRP) are phytopathogens of the genera Pectobacterium and Dickeya that cause soft rots on a wide range of crops and ornamental plants. SRP produce plant cell wall degrading enzymes (PCWDEs), including pectinases. Bdellovibrio and like organisms are bacterial predators that can prey on a variety of Gram‐negative species, including SRP. In this research, a low methoxyl pectin (LMP)‐based immobilization system for B. bacteriovorus is established. It takes advantage that pectin residues induce PCWDE secretion by the pathogens, bringing upon the release of the encapsulated predators. Three commercial LMPs differing in the degree of esterification (DE) and amidation (DA) were tested as potential carriers, by examining their effect on SRP growth, enzymes secretion and substrate breakdown. A clear advantage was observed for pectin 5 CS with the lowest DE and DA content. The degradation of 5 CS pectin‐based carriers was further optimized by reducing cross‐linker and pectin concentration, by adding gelatin and by dehydration. This resulted in SRP‐induced disintegration of the carrier within 72 h. The released encapsulated predator caused a large decrease in SRP population while its own significantly increased, demonstrating the efficiency of this system in which the pathogen brings about its own demise. [ABSTRACT FROM AUTHOR]

Summary: Bdellovibrio and like organisms (BALOs) prey on Gram‐negative bacteria in the planktonic phase as well as in biofilms, with the ability to reduce prey populations by orders of magnitude. During the last few years, evidence has mounted for a significant ecological role for BALOs, with important implications for our understanding of microbial community dynamics as well as for applications against pathogens, including drug‐resistant pathogens, in medicine, agriculture and aquaculture, and in industrial settings for various uses. However, our understanding of biofilm predation by BALOs is still very fragmentary, including gaps in their effect on biofilm structure, on prey resistance, and on evolutionary outcomes of both predators and prey. Furthermore, their impact on biofilms has been shown to reach beyond predation, as they are reported to reduce biofilm structures of non‐prey cells (including Gram‐positive bacteria). Here, we review the available literature on BALOs in biofilms, extending known aspects to potential mechanisms employed by the predators to grow in biofilms. Within that context, we discuss the potential ecological significance and potential future utilization of the predatory and enzymatic possibilities offered by BALOs in medical, agricultural and environmental applications. [ABSTRACT FROM AUTHOR]

Bdellovibrio-and-like organisms (BALOs) are peculiar, ubiquitous, small-sized, highly motile Gram-negative bacteria that are obligatory predators of other bacteria. Typically, these predators invade the periplasm of their prey where they grow and replicate. To date, BALOs constitute two highly diverse families affiliated with the δ- proteobacteria class. In this study, Micavibrio spp., a BALO lineage of epibiotic predators, were isolated from soil. These bacteria attach to digest and grow at the expense of other prokaryotes, much like other BALOs. Multiple phylogenetic analyses based on six genes revealed that they formed a deep branch within the α- proteobacteria, not affiliated with any of the α-proteobacterial orders. The presence of BALOs deep among the α- proteobacteria suggests that their peculiar mode of parasitism maybe an ancestral character in this proteobacterial class. The origin of the mitochondrion from an α- proteobacterium endosymbiont is strongly supported by molecular phylogenies. Accumulating data suggest that the endosymbiont’s host was also a prokaryote. As prokaryotes are unable to phagocytose, the means by which the endosymbiont gained access into its host remains mysterious. We here propose a scenario based on the BALO feeding-mode to hypothesize a mechanism at play at the origin of the mitochondrial endosymbiosis. [ABSTRACT FROM AUTHOR]

Bdellovibrio-and-like organisms (BALOs) are widespread obligatory predators of other Gram-negative bacteria. Their detection by culture-dependent methods is complicated as their replication is totally dependent upon the availability of an appropriate prey. Because BALOs do not form numerically dominant groups within microbial communities, non-specific culture-independent tools also generally fail to detect them. We designed sets of 16S rRNA primers that specifically target BALOs. Polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) were combined, yielding partial 16S rDNA sequences. This simple method that allows specific in situ culture-independent detection of BALOs was applied to the soil environment. Bdellovibrio-and-like organisms were also isolated from the same soil and the phylogeny and prey range of the isolates analysed. Seventeen isolates retrieved using five different potential preys exhibited eight different spectra of prey utilization and formed nine operational taxonomic units (OTUs). These OTUs were affiliated with the Bdellovibrionaceae, Bacteriovorax, Peredibacter or Micavibrio, i.e. the known BALO groups. In comparison, 15 OTUs including 10 that were not detected by the culture-dependent approach were obtained using the specific primers in a PCR-DGGE approach. The occurrence of a complex BALO community suggests that predation occurs on a much wider range of prey than can be detected by the classical culture-dependent technique. [ABSTRACT FROM AUTHOR]

Predation at the lowest trophic level, i.e. between bacteria, is poorly understood, hindering efforts to assess its impact on the structure of bacterial communities. The interaction of Bdellovibrio and Bacteriovorax ( Bdellovibrio and like organisms, BLOs), a group of obligate, ubiquitous predatory bacteria, with their Gram-negative bacterial prey results in the multiplication of the predator and in the lysis, but not in the eradication, of the prey. We show that the residual, surviving populations of prey cells exposed to predation stress differ from the populations before exposure, as they exhibit increased resistance to predation. This resistance was demonstrated in a number of Gram-negative prey. Moreover, predation resistance is not specific for the BLO strain experienced by the prey. The phenomenon does not stem from a mutation but is a plastic response associated with a phenotypic change, and it disappears upon removal of the predator. As resistance to predation is not total, this mechanism can ensure survival of both predator and prey. [ABSTRACT FROM AUTHOR]

Host-independent (H-I) mutants of the obligate bacterial parasite Bdellovibrio bacteriovorus were isolated from wild-type strain 109J. Seven H-I mutants differed in morphological features such as cell length (2–30 µm) and shape (short or long spirals or rod-like), plaque size, and pigmentation (from almost colorless to bright orange). The mutants exhibited widely different growth capabilities in rich medium, with biomass doubling times and final biomass varying by a factor of two or more. Growth was always enhanced by the addition of host cell extract or divalent cations to the growth medium, but the effect varied widely between the mutants. Analysis of the hit region, mutations in which were previously proposed to be associated with the H-I phenotype, revealed that changes in the nucleotide sequence in this region occurred only in three of the seven mutants. [ABSTRACT FROM AUTHOR]

Bacterial soft rot diseases caused by Pectobacterium spp. and Dickeya spp. affect a wide range of crops, including potatoes, a major food crop. As of today, farmers mostly rely on sanitary practices, water management, and plant nutrition for control. We tested the bacterial predators Bdellovibrio and like organisms (BALOs) to control potato soft rot. BALOs are small, motile predatory bacteria found in terrestrial and aquatic environments. They prey on a wide range of Gram-negative bacteria, including animal and plant pathogens. To this end, BALO strains HD100, 109J, and a ΔmerRNA derivative of HD100 were shown to efficiently prey on various rot-causing strains of Pectobacterium and Dickeya solani. BALO control of maceration caused by a highly virulent strain of Pectobacterium carotovorum subsp. brasilense was then tested in situ using a potato slice assay. All BALO strains were highly effective at reducing disease, up to complete prevention. Effectivity was concentration dependent, and BALOs applied before P. carotovorum subsp. brasilense inoculation performed significantly better than those applied after the disease-causing agent, maybe due to in situ consumption of glucose by the prey, as glucose metabolism by live prey bacteria was shown to prevent predation. Dead predators and the supernatant of BALO cultures did not significantly prevent maceration, indicating that predation was the major mechanism for the prevention of the disease. Finally, plastic resistance to predation was affected by prey and predator population parameters, suggesting that population dynamics affect prey response to predation. [ABSTRACT FROM AUTHOR]

Bdellovibrio and like organisms are obligate predators of bacteria that are ubiquitously found in the environment. Most exhibit a peculiar dimorphic life cycle during which free-swimming attack-phase (AP) cells search for and invade bacterial prey cells. The invader develops in the prey as a filamentous potynucleoid- containing cell that finally splits into progeny cells. Therapeutic and biocontrol applications of Bdellovibrio in human and animal health and plant health, respectively, have been proposed, but more knowledge of this peculiar cell cycle is needed to develop such applications. A proteomic approach was applied to study cell cycle-dependent expression of the Bdellovibrio bacteriovorus proteome in synchronous cultures of a facultative host-independent (HI) strain able to grow in the absence of prey. Results from two-dimensional gel electro- phoresis, mass spectrometry, and temporal expression of selected genes in predicted operons were analyzed. In total, about 21% of the in silico predicted proteome was covered. One hundred ninety-six proteins were identified, including 63 hitherto unknown proteins and 140 life stage-dependent spots. Of those, 47 were differentially expressed, including chemotaxis, attachment, growth- and replication-related, cell wall, and regulatory proteins. Novel cell cycle-dependent adhesion, gliding, mechanosensing, signaling, and hydrolytic functions were assigned. The HI model was further studied by comparing HI and wild-type AP cells, revealing that proteins involved in DNA replication and signaling were deregulated in the former. A complementary analysis of the secreted proteome identified 59 polypeptides, including cell contact proteins and hydrolytic enzymes specific to predatory bacteria. [ABSTRACT FROM AUTHOR]

A two-dimensional electrophoretic analysis of protein distribution followed by identification of selected proteins by mass spectrometry was performed on fresh bdellovibrio cultures containing attack phase cells of the predatory bacterium Bdellovibrio bacteriovorus strain 109J-1 and the remains of an Escherichia coli or a Pseudomonas syringae pv. tomato prey. Cleavage of the peptidoglycan-associated outer membrane proteins (OMPs) OmpA in E. coli and OprF in P. syringae occurred in both prey. The tryptic peptides obtained from the cleavage products of OmpA and OprF were all located within the 19-kDa pronase-resistant N-terminal parts of the corresponding proteins. The predator cell fraction was separated from the prey ghosts in fresh bdellovibrio cultures by centrifugation on a Percoll-sucrose cushion. Proteins from each fraction were separated by two-dimensional electrophoresis and identified by mass spectrometric analysis. As no prey OMP could be detected in the predator cell fraction, it was concluded that prey OMPs are not transferred to the predator, as had been suggested previously. However, a protein from the predator was found bound to ghost cell envelopes. This protein may correspond to a protein earlier suggested to be associated with the prey outer or cytoplasmic membranes. Along with recently described polypeptides from B. bacteriovorus strains 100 and 114, it forms a new family of putative outer membrane proteins. [ABSTRACT FROM AUTHOR]