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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]

Polyphagous, holometabolous insects adapt to rapid diet shifts imposed by their ecology and their life cycle. One shift is linked to development, as larvae and adults usually dwell and feed in different environments, using different resources. The second is caused by changes in larval hosts, often occurring at each generation. Studies show that the insect's microbiome also changes in relation to development and larval host. However, parental and larval host contributions to its structure and trans‐generational dynamics remain uncharted.We investigated the sources of variation of the microbiome of the highly polyphagous Mediterranean fruit fly by tracking microbiome structure and its potential functional impact in fly lineages over generations and fruit host shifts, using 16S rRNA gene amplicon single variant analysis.Bacterial community alpha‐diversity expanded and contracted cyclically in a life stage‐dependent manner with the mothers' microbiome community 'resetting' to the same structure across generations. Expansion occurred at the larval stage, while alpha‐diversity decreased in tenerals, and significantly in mothers. In contrast, richness was highest in mothers, with rare taxa expanding in larvae depending upon fruit type.Metabolic predictions using PICRUSt pointed to increased metabolism of vitamins in mothers, and of aromatic compouds in larvae and tenerals, while indicator species analysis suggested fruit host composition‐dependent potential functional adaptations.Our data indicate lineage, fruit host and their interactions as the main sources of microbiome variation and provide examples of possible metabolic developmental and ecological adaptations. Taken together, these data support the hypothesis that microbiome diversity and microbiome‐driven local adaptations act as a mechanism sustaining polyphagy. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Antibiotic resistance (AR) in bacteria is an urgent and global health issue, encompassing clinical, agricultural, terrestrial and aquatic environments. 13 Hobley, L., Summers, J.K., Till, R., Milner, D.S., Atterbury, R.J., Stroud, A., et al. (2020) Dual predation by bacteriophage and Bdellovibrio bacteriovorus can eradicate Escherichia coli prey in situations where single predation cannot. I bacteriovorus i predation, and that phenotypically predation-resistant cells do not exhibit increased AR. Furthermore, genetic resistance in BALOs is little understood: BALOs strains belonging to the same species differ in prey range, and different prey strains belonging to the same species may also be differentially preyed upon by a particular BALO (Dashiff I et al i ., 2011). [Extracted from the article]

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]

Summary: Domestication disconnects an animal from its natural environment and diet, imposing changes in the attendant microbial community. We examine these changes in Philornis downsi (Muscidae), an invasive parasitic fly of land birds in the Galapagos Islands. Using a 16S rDNA profiling approach we studied the microbiome of larvae and adults of wild and laboratory‐reared populations. These populations diverged in their microbiomes, significantly more so in larval than in adult flies. In field‐collected second‐instar larvae, Klebsiella (70.3%) was the most abundant taxon, while in the laboratory Ignatzschineria and Providencia made up 89.2% of the community. In adults, Gilliamella and Dysgonomonas were key members of the core microbiome of field‐derived females and males but had no or very low representation in the laboratory. Adult flies harbour sex‐specific microbial consortia in their gut, as male core microbiomes were significantly dominated by Klebsiella. Thus, P. downsi microbiomes are dynamic and shift correspondingly with life cycle and diet. Sex‐specific foraging behaviour of adult flies and nest conditions, which are absent in the laboratory, may contribute to shaping distinct larval, and adult male and female microbiomes. We discuss these findings in the context of microbe–host co‐evolution and the implications for control measures. [ABSTRACT FROM AUTHOR]

Summary: Natural landscapes are both fragmented and heterogeneous, affecting the distribution of organisms, and their interactions. While predation in homogeneous environments increases the probability of population extinction, fragmentation/heterogeneity promotes coexistence and enhances community stability as shown by experimentation with animals and microorganisms, and supported by theory. Patch connectivity can modulate such effects but how microbial predatory interactions are affected by water‐driven connectivity is unknown. In soil, patch habitability by microorganisms, and their connectivity depend upon the water saturation degree (SD). Here, using the obligate bacterial predator Bdellovibrio bacteriovorus, and a Burkholderia prey, we show that soil spatial heterogeneity profoundly affects predatory dynamics, enhancing long‐term co‐existence of predator and prey in a SD‐threshold dependent‐manner. However, as patches and connectors cannot be distinguished in these soil matrices, metapopulations cannot be invoked to explain the dynamics of increased persistence. Using a set of experiments combined with statistical and physical models we demonstrate and quantify how under full connectivity, predation is independent of water content but depends on soil microstructure characteristics. In contrast, the SD below which predation is largely impaired corresponds to a threshold below which the water network collapses and water connectivity breaks down, preventing the bacteria to move within the soil matrix. [ABSTRACT FROM AUTHOR]

Summary: Bdellovibrio and like organisms (BALOs) are largely distributed in soils and in water bodies obligate predators of gram‐negative bacteria that can affect bacterial communities. Potential applications of BALOs include biomass reduction, their use against pathogenic bacteria in agriculture, and in medicine as an alternative against antibiotic‐resistant pathogens. Such different environments and uses mean that BALOs should be active under a range of viscosities. In this study, the predatory behaviour of two strains of the periplasmic predator B. bacteriovorus and of the epibiotic predator Micavibrio aeruginosavorus was examined in viscous polyvinylpyrrolidone (PVP) solutions at 28 and at 37°C, using fluorescent markers and plate counts to track predator growth and prey decay. We found that at high viscosities, although swimming speed was largely decreased, the three predators reduced prey to levels similar to those of non‐viscous suspensions, albeit with short delays. Prey motility and clumping did not affect the outcome. Strikingly, under low initial predator concentrations, predation dynamics were faster with increasing viscosity, an effect that dissipated with increasing predator concentrations. Changes in swimming patterns and in futile predator–predator encounters with viscosity, as revealed by path analysis under changing viscosities, along with possible PVP‐mediated crowding effects, may explain the observed phenomena. [ABSTRACT FROM AUTHOR]

Summary: Wastewater purification is mostly performed in activated sludge reactors by bacterial and microeukaryotic communities, populating organic flocs and a watery liquor. While there are numerous molecular community studies of the bacterial fraction, those on microeukaryotes are rare. We performed a year‐long parallel 16S rRNA gene and 18S rRNA‐gene based analysis of the bacterial and of the microeukaryote communities, respectively, of physically separated flocs and particle‐free liquor samples from three WWTPs. This uncovered a hitherto unknown large diversity of microeukaryotes largely composed of potential phagotrophs preferentially feeding on either bacteria or other microeukaryotes. We further explored whether colonization of the microhabitats was selective, showing that for both microbial communities, different but often closely taxonomically and functionally related populations exhibiting different dynamic patterns populated the microhabitats. An analysis of their between plants‐shared core populations showed the microeukaryotes to be dispersal limited in comparison to bacteria. Finally, a detailed analysis of a weather‐caused operational disruption in one of the plants suggested that the absence of populations common to the floc and liquor habitat may negatively affect resilience and stability. [ABSTRACT FROM AUTHOR]

The composition and diversity of bacteria forming the microbiome of parasitic organisms have implications for differential host pathogenicity and host-parasite co-evolutionary interactions. The microbiome of pathogens can therefore have consequences that are relevant for managing disease prevalence and impact on affected hosts. Here, we investigate the microbiome of an invasive parasitic fly Philornis downsi, recently introduced to the Galápagos Islands, where it poses extinction threat to Darwin's finches and other land birds. Larvae infest nests of Darwin's finches and consume blood and tissue of developing nestlings, and have severe mortality impacts. Using 16s rRNA sequencing data, we characterize the bacterial microbiota associated with P. downsi adults and larvae sourced from four finch host species, inhabiting two islands and representing two ecologically distinct groups. We show that larval and adult microbiomes are dominated by the phyla Proteobacteria and Firmicutes, which significantly differ between life stages in their distributions. Additionally, bacterial community structure significantly differed between larvae retrieved from strictly insectivorous warbler finches ( Certhidea olivacea) and those parasitizing hosts with broader dietary preferences (ground and tree finches, Geospiza and Camarhynchus spp., respectively). Finally, we found no spatial effects on the larval microbiome, as larvae feeding on the same host (ground finches) harboured similar microbiomes across islands. Our results suggest that the microbiome of P. downsi changes during its development, according to dietary composition or nutritional needs, and is significantly affected by host-related factors during the larval stage. Unravelling the ecological significance of bacteria for this parasite will contribute to the development of novel, effective control strategies. [ABSTRACT FROM AUTHOR]

Bdellovibrio bacteriovorus HD100 is an obligate predator that invades and grows within the periplasm of Gram-negative bacteria, including mcl-polyhydroxyalkanoate ( PHA) producers such as Pseudomonas putida. We investigated the impact of prey PHA content on the predator fitness and the potential advantages for preying on a PHA producer. Using a new procedure to control P. putida KT2442 cell size we demonstrated that the number of Bdellovibrio progeny depends on the prey biomass and not on the viable prey cell number or PHA content. The presence of mcl- PHA hydrolysed products in the culture supernatant after predation on P. putida KT42Z, a PHA producing strain lacking PhaZ depolymerase, confirmed the ability of Bdellovibrio to degrade the prey's PHA. Predator motility was higher when growing on PHA accumulating prey. External addition of PHA polymer (latex suspension) to Bdellovibrio preying on the PHA minus mutant P. putida KT42C1 restored predator movement, suggesting that PHA is a key prey component to sustain predator swimming speed. High velocities observed in Bdellovibrio preying on the PHA producing strain were correlated to high intracellular ATP levels of the predator. These effects brought Bdellovibrio fitness benefits as predation on PHA producers was more efficient than predation on non-producing bacteria. [ABSTRACT FROM AUTHOR]

Summary Insects form an extremely large group of animals and bear a consequently large variety of associated microbes. This microbiota includes very specific and obligate symbionts that provide essential functions to the host, and facultative partners that are not necessarily required for survival. The Tephritidae is a large family that includes many fruit pests such as the Mediterranean fruit fly (the medfly, Ceratitis capitata) and the Olive fly ( Bactrocera oleae). Community and functional analyses showed that the microbiota of both flies contribute to their diet, and affect host fitness parameters. The analysis of the microbiota's community structure of mass-reared, sterilized medfly males used in the sterile insect technique revealed a strong reduction in Klebsiella spp. compared with non-sterile and wild flies. Inoculation of sterile males with this gut population affected female mating behaviour as they preferentially mated with inoculated versus non-inoculated males. These studies suggest that control can be significantly improved by manipulating symbionts in pest animals. [ABSTRACT FROM AUTHOR]

An essay is presented on the origin of eukaryotic cell. It hypothesizes that a form of microbial parasitism or predation between prokaryotes played an important role in the eukaryotic cell evolution. It also explores the phylogenetic origin of mitochondria to demonstrate the host dependency of protomitochondrion. It suggests that symbiotic mutualistic interaction might be a result of the interaction between two prokaryotes, which started with a predatory relation.

Mediterranean fruit flies ( Ceratitis capitata Wiedemann, Diptera: Tephritidae) harbor a community of diazotrophic bacteria in their digestive system. The present study aims to test the hypothesis that bacteria contribute to fly fitness by enhancing copulatory success and egg production in males and females, respectively. After eclosion, flies were fed a full diet containing peptides, sugar and minerals, or a sugar diet, lacking peptides. Subgroups from each diet were fed a mixture of the antibiotics ciprofloxacin and piperacillin. The presence of bacteria, food consumption, weight gain, lipid and protein levels, oviposition in females and copulatory success of males were quantified in the four groups. The antibiotic treatment effectively cleared the gut of bacteria. The relative amounts of food consumed (with or without antibiotics) are similar in all groups. The antibiotics do not inhibit feeding, and their ingestion does not affect dry weight or the amount of protein stored, yet females feeding on the full diet without antibiotics have increased lipid levels. Females fed the full diet produce significantly more eggs than females on the sugar diet, but the presence of bacteria does not affect numbers of eggs produced. However, in the absence of bacteria, the oviposition rate of nutritionally stressed females is significantly accelerated. The presence of bacteria in sugar fed males does not provide them with a mating advantage. Conversely, in males fed a full diet, the presence of bacteria is associated significantly with a shorter latency to mate. It is concluded that, because the bacterial community is present at all stages of the fly’s life cycle, at least some species are effectively transmitted from parents to offspring, and removal of bacteria affects measurable physiological and behavioural parameters related to fitness, the association between bacteria and the medfly is mutualistic. [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]

Positive response of plant species to plant growth-promoting rhizobacteria have led to an increased interest in their use as bacterial inoculants. However, the introduction of exogenous bacteria into natural ecosystems may perturb bacterial populations within the microbial community and lead to the disruption of indigenous populations performing key functional roles. In this study the effect of Azospirillum brasilense inoculation on maize ( Zea mays) rhizosphere Actinobacteria, Bacteroidetes, α- Proteobacteria, Pseudomonas and Bdellovibrio spp. was assessed using a polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) approach in conjunction with group-specific primers. The DGGE fingerprints analysis revealed that the introduction of A. brasilense did not alter or disrupt the microbial system at the group-specific level. However, some communities such as the α- Proteobacteria and Bdellovibrio were influenced by plant age while the other bacterial groups remained unaffected. Based on these as well as previous data, it can be inferred that inoculation with A. brasilense does not perturb the natural bacterial populations investigated. [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]

A letter to the editor is presented in response to the article "Evaluating Hypotheses for the Origin of Eukaryotes," by A. M. Poole and D. Penny that appeared in a previous issue of this periodical.