Chemotaxis by Bdellovibrio bacteriovorus toward prey.

A chemotaxis assay system that uses a modified Boyden chamber was characterized and used for measurements of chemotaxis by Bdellovibrio bacteriovorus strain UKi2 toward several bacterial species. Bacteria tested included both susceptible and nonsusceptible cells (Escherichia coli, Pseudomonas fluorescens, Bacillus megaterium, and B. bacteriovorus strains UKi2 and D). None was attractive to bdellovibrios when present at densities below 10(7) cells per ml. Chemotaxis toward E. coli was studied most extensively; under conditions that minimized effects of osmotic shock to the cells, E. coli and exudates from E. coli at densities as high as 10(8) cells per ml failed to elicit a chemotactic response. Cell-free filtrates from mixed cultures of bdellovibrios and E. coli neither attracted nor repelled bdellovibrios. The data indicate that bdellovibrios do not use chemotaxis to locate prey cells.     

Bdellovibrio predation in the presence of decoys: Three-way bacterial interactions revealed by mathematical and experimental analyses

Bdellovibrio bacteriovorus is a small, gram-negative, motile bacterium that preys upon other gram-negative bacteria, including several known human pathogens. Its predation efficiency is usually studied in pure cultures containing solely B. bacteriovorus and a suitable prey. However, in natural environments, as well as in any possible biomedical uses as an antimicrobial, Bdellovibrio is predatory in the presence of diverse decoys, including live nonsusceptible bacteria, eukaryotic cells, and cell debris. Here we gathered and mathematically modeled data from three-member cultures containing predator, prey, and nonsusceptible bacterial decoys. Specifically, we studied the rate of predation of planktonic late-log-phase Escherichia coli S17-1 prey by B. bacteriovorus HD100, both in the presence and in the absence of Bacillus subtilis nonsporulating strain 671, which acted as a live bacterial decoy. Interestingly, we found that although addition of the live Bacillus decoy did decrease the rate of Bdellovibrio predation in liquid cultures, this addition also resulted in a partially compensatory enhancement of the availability of prey for predation. This effect resulted in a higher final yield of Bdellovibrio than would be predicted for a simple inert decoy. Our mathematical model accounts for both negative and positive effects of predator-prey-decoy interactions in the closed batch environment. In addition, it informs considerations for predator dosing in any future therapeutic applications and sheds some light on considerations for modeling the massively complex interactions of real mixed bacterial populations in nature.     

Size-dependent predation risk in cryptic prey

Journal of Ethology - Visual crypsis of prey is determined by the interaction between an individual’s physical appearance to their predators and visual aspects of their environment. Physical...     

Population and behavioural responses of native prey to alien predation

The introduction of invasive alien predators often has catastrophic effects on populations of naïve native prey, but in situations where prey survive the initial impact a predator may act as a strong selective agent for prey that can discriminate and avoid it. Using two common species of Australian small mammals that have persisted in the presence of an alien predator, the European red fox Vulpes vulpes, for over a century, we hypothesised that populations of both would perform better where the activity of the predator was low than where it was high and that prey individuals would avoid signs of the predator’s presence. We found no difference in prey abundance in sites with high and low fox activity, but survival of one species—the bush rat Rattus fuscipes—was almost twofold higher where fox activity was low. Juvenile, but not adult rats, avoided fox odour on traps, as did individuals of the second prey species, the brown antechinus, Antechinus stuartii. Both species also showed reduced activity at foraging trays bearing fox odour in giving-up density (GUD) experiments, although GUDs and avoidance of fox odour declined over time. Young rats avoided fox odour more strongly where fox activity was high than where it was low, but neither adult R. fuscipes nor A. stuartii responded differently to different levels of fox activity. Conservation managers often attempt to eliminate alien predators or to protect predator-naïve prey in protected reserves. Our results suggest that, if predator pressure can be reduced, otherwise susceptible prey may survive the initial impact of an alien predator, and experience selection to discriminate cues to its presence and avoid it over the longer term. Although predator reduction is often feasible, identifying the level of reduction that will conserve prey and allow selection for avoidance remains an important challenge.     

Effect of paracrystalline protein surface layers on predation by Bdellovibrio bacteriovorus.

We determined that paracrystalline protein surface arrays (S layers) protected gram-negative eubacteria from predation by Bdellovibrio bacteriovorus. Aquaspirillum serpens VHA and MW5 and Aquaspirillum sinuosum were resistant to predation by B. bacteriovorus 6-5-S when fully covered by their S layers. The S layer of Aeromonas salmonicida A449 protected the cells from predication by B. bacteriovorus 109J. A predacious, plaque-forming vibrio that lysed an S-layer- variant of Caulobacter crescentus but was not predacious on the parental strain which possessed an S layer was isolated from raw sewage. Since S layers are stable components of many bacterial surfaces in nature, they can provide this protective function in both aquatic and terrestrial habitats where Bdellovibrio spp. are found.     

Predatory Bdellovibrio bacteria use gliding motility to scout for prey on surfaces

Bdellovibrio bacteriovorus is a famously fast, flagellate predatory bacterium, preying upon Gram-negative bacteria in liquids; how it interacts with prey on surfaces such as in medical biofilms is unknown. Here we report that Bdellovibrio bacteria "scout" for prey bacteria on solid surfaces, using slow gliding motility that is present in flagellum-negative and pilus-negative strains.     

Frequency-dependent predation and maintenance of prey polymorphism

In positive frequency-dependent predation, predation risk of an individual prey correlates positively with the frequency of that prey type. In a number of small-scale experiments individual predators have shown frequency-dependent behaviour, often leading to the conclusion that a population of such predators could maintain prey polymorphism. Using simulations, I studied the dynamics of frequency-dependent predation and prey polymorphism. The model suggests that persistence of prey polymorphism decreases with increasing number of predators that show frequency-dependent behaviour, questioning conclusions about polymorphism based on experiments with few predators. In addition, prey population size, prey crypsis, difference in crypsis between prey morphs and the way the behaviour was adjusted affected the persistence of polymorphism. Under some circumstances prey population remained polymorphic for a shorter time under frequency-dependent than under frequency-independent predation. This suggests that although positive frequency-dependent predator behaviour may maintain prey polymorphism, it is not a sufficient condition for persistent prey polymorphism.     

Site selection under differential predation risks by drifting prey in streams

We derived a model to predict site selection by drifting prey in streams. This model considers the conflicting demands between feeding and avoiding both benthic and drift predators. Our analysis suggests a ranking of site qualities based on the ratio of food acquisition rate to benthic predation risk (termed site value). Drifting organisms should accept a given site type when its site value exceeds the expected value of drifting, which is the average site value prey are likely to encounter adjusted for the costs of drifting. These costs are represented as drift predation risk and time that is lost from foraging as prey search for a better site. We contend that prey should rank site types in descending order based on site value and sequentially add site types to the acceptable category in order of highest rank until the addition of the next lowest ranked site decreases rather than increases the expected value of drifting. The best sites should be those with high food availability and low benthic predation risk. Prey should reject a site when drift predation risk is low, the proportion of acceptable site types is high, and the rate that prey settle from the drift is high. Interestingly, prey with the greatest locomotory ability should have the greatest propensity to drift because these individuals spend less time drifting, making them less susceptible to drift predators. Our model provides a framework to simultaneously integrate the effects of food availability, benthic predation risk, and drift predation risk on site selection of actively drifting prey.     

Habitat selection by predators and prey in communities with asymmetrical intraguild predation

Competition and predation have broad ecological consequences as they may influence individual behavior and community structure. In some cases, they are linked and predator and prey are also competitors (intraguild predation). I present a game theoretic model of habitat use by predators and prey under conditions of asymmetrical intraguild predation. This model predicts that when the diet of intraguild predators is restricted to intraguild prey and the resource for which predators and prey compete (the basal resource), co-occurrence is only stable when dietary overlap is low and productivity of the basal resource is not high. The addition of alternative resources for predators results in co-occurrence under all conditions. Variation in alternative resource productivity produces a continuum of intraguild prey distributions from matching relative habitat safety, to one that reflects both food and predation risk. When there is a substantial alternative resource for predators, the distribution of predators matches that of alternative resource availability while the distribution of prey is influenced by both habitat riskiness and food availability. The density and distribution of the predator's alternative resource thus influence habitat selection by the intraguild prey. This stresses the importance of indirect interactions in structuring habitat use in communities and the need to view habitat selection in a community context.     

Combining bacterial blight resistance and Basmati quality characteristics by phenotypic and molecular marker-assisted selection in rice

Bacterial Blight (BB) caused by Xanthomonas oryzae pv. oryzae is a major disease of rice in tropical Asia. Since all the Basmati varieties are highly susceptible and the disease is prevalent in the entire Basmati growing region of India, BB is a severe constraint in Basmati rice production. The present study was undertaken with the objective of combining the important Basmati quality traits with resistance to BB by a combination of phenotypic and molecular marker-assisted selection (MAS). Screening of 13 near-isogenic lines of rice against four isolates of the pathogen from Basmati growing regions identified the Xa4, xa8, xa13 and Xa21 effective against all the isolates tested. Two or more of these genes in combination imparted enhanced resistance as expressed by reduced average lesion length in comparison to individual genes. The two-gene pyramid line IRBB55 carrying xa13 and Xa21 was found equally effective as three/four gene pyramid lines. The two BB resistance genes present in IRBB55 were combined with the Basmati quality traits of Pusa Basmati-1 (PB-1), the most popular high yielding Basmati rice variety used as recurrent parent. Phenotypic selection for disease resistance, agronomic and Basmati quality characteristics and marker-assisted selection for the two resistance genes were carried out in BC₁F₁, BC₁F₂ and BC₁F₃ generations. Background analysis using 252 polymorphic amplified fragment length polymorphism (AFLP) markers detected 80.4 to 86.7% recurrent parent alleles in BC₁F₃ selections. Recombinants having enhanced resistance to BB, Basmati quality and desirable agronomic traits were identified, which can either be directly developed into commercial varieties or used as immediate donors of BB resistance in Basmati breeding programs.     

Nonlinearity in the predation risk of prey mobility

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey which increase their mobility in order to disperse and dilute their waste should avoid a high predation risk until this benefit is balanced by the increasing risks of random predator encounter. This hypothesis was tested for voles (Microtus spp.) in Finland which are vulnerable to predation due to the scent and ultraviolet attractiveness of their urine. The mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggest that predation risk can exert strong selective pressures on prey such that they have little respite from the risk of being killed.     

Stimulation of bacterial cytokinesis by bacteriophage predation

Bacteriophage (phage) are ubiquitous in the water column and in the sediments of most natural water. Because of their colloidal nature, they can either aggregate into clumps large enough to settle into the sediment or departing upon the physiochemical conditions or disassociate and reenter the water column. About 80% of the bacterial strains isolated from New River sediment have a virulent phage that can be isolated with them.Liquid cultures of a strain of Pseudomonas aeruginosa isolated from the New River along with its phage were set up. One was infected with the virulent phage and another kept as a control. Daily counts were made of bacterial numbers. After 10 days the control culture was infected and counted for 3 more days.Both cultures divided exponentially at first. The infected culture continued to divide at about half the initial rate. The uninfected culture nearly ceased division, but when phage were added it quickly began to divide.The virulent phage infection clearly stimulated host division. The effect was to establish itself as an endemic infection which did not outpace its host's division rate. Further, the enhanced division rate may act to increase the host's share of available nutrients and benefit its competitive position in the system.     

Effect of disease-selective predation on prey infected by contact and external sources

We propose and analyze a simple mathematical model for susceptible prey (S)–infected prey (I)–predator (P) interaction, where the susceptible prey population (S) is infected directly from external sources as well as through contact with infected class (I) and the predator completely avoids consuming the infected prey. The model is analyzed to obtain different thresholds of the key parameters under which the system exhibits stability around the biologically feasible equilibria. Through numerical simulations we display the effects of external infection and the infection through contact on the system dynamics in the absence as well as in the presence of the predator. We compare the system dynamics when infection occurs only through contact, with that when it occurs through contact and external sources. Our analysis demonstrates that under a disease-selective predation, stability and oscillations of the system is determined by two key parameters: the external infection rate and the force of infection through contact. Due to the introduction of external infection, the predator and the prey population show limit-cycle oscillations over a range parametric values. We suggest that while predicting the dynamics of such an eco-epidemiological system, the modes of infection and the infection rates might be carefully investigated.     

Post-encounter vulnerability of some rotifer prey types to predation by the copepod Acanthocyclops robustus

Prey characteristics affecting vulnerability of a number of rotifer species to the predator Acanthocyclops robustus were investigated. Body volume was the main feature affecting the probability of attack after encounter and, with the exception of Polyarthra major, capture after attack. The lorica provided protection against predation in some species and a skipping escape response reduced the likelihood of capture in Polyarthra major.     

Fate of predator and prey proteins during growth of Bdellovibrio bacteriovorus on Escherichia coli and Pseudomonas syringae prey

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.     

Some aspects of vulnerability to cyclopoid predation of zooplankton prey individuals

The predation cycle (encounter, attack, capture and ingestion or survival) by adult female Acanthocyclops robustus was observed for four crustacean prey types. The chief defense of A. robustus nauplii was escape response ability, reducing the probability of capture after attack, and, most likely, attack after encounter. The most important feature reducing the vulnerability of Ceriodaphnia and Daphnia species was large body size, decreasing the probability of capture after attack. Escape response ability and carapace strength/integrity further reduced vulnerability. Carapace strength/integrity was an effective defense for Bosmina longirostris, reducing the probability of ingestion after capture.The predation cycle by juvenile A. robustus was examined for three prey types. All three prey types seemed to be readily attacked. Due to their possession of loricae, Keratella cochlearis and Pompholyx sulcata were seldom eaten, while the illoricate Synchaeta kitina was highly vulnerable.Egg vulnerability after attack by the adult female predator was analysed. The eggs of Brachionus calyciflorus, Pompholyx sulcata and Filinia longiseta were rarely eaten, although the adults of the latter were usually ingested (thus causing the eggs to float free). Out of three attacks recorded on Keratella Quadrata, the eggs were eaten (or destroyed) twice.Handling times by the adult female predator were measured for a number of prey types. The shortest mean handling time was for Synchaeta kitina (less than one second), while the longest was on Ceriodaphnia species (716 seconds). Results were quite variable. Handling time was significantly positively related to prey body volume, while exoskeletal strength/integrity also increased this time. No effect of temperature on handling time was found for Synchaeta pectinata or Polyarthra major between 15 and 26.5 °C.     

Individual vulnerability to predation: the effect of alternative prey types

SUMMARY. 1. Many examples of predator-prey interactions from freshwaters suggest that apparent predator preferences result more from the relative vulnerabilities of prey than any positive choice by the predator.
2. The rank order of vulnerability of seven invertebrate prey to nine invertebrate predators was measured in the laboratory. The ranks were used as a measure of relative vulnerability.
3. The vulnerability of individuals of Simocephalus vetulus (Muller) (Crustacea: Cladocera) to predation by Enallagma cyathigerum (Char-pentier) (Insecta: Odonata) and Notonecta glauca L, (Insecta: Hemiptera) was investigated in the presence of alternative prey of differing relative vulnerabilities, based on the rank order measures.
4. With E. cyathigerum , vulnerability of individual S. vetulus depended greatly on the relative vulnerability of other prey types available. With N. glauca the intrinsic defences of S. vetulus were very effective.
5. The importance of relative prey vulnerability is discussed with particular reference to small habitats with marked annual species turnover.     

Chaoborus predation and the function of phenotypic variation in Daphnia

To investigate the role of helmet formation in defense against predation, laboratory experiments were used to analyze the effects of morphological changes in Daphnia on susceptibility to Chaoborus predation. Behavioral observations of Chaoborus preying on helmeted and non-helmeted Daphnia suggest pre-contact advantages for helmeted prey but post-contact advantages for non-helmeted prey. Helmeted Daphnia are better at evading capture by Chaoborus but may also be more easily handled by the predator. Swimming behavior of the prey, which is influenced by the presence of a tailspine, may affect Chaoborus strike distance. These results re-emphasize the potential hydromechanical importance of body shape changes in defense against predation.