Bacterial predation under changing viscosities

Abstract

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.

Potential Control of Potato Soft Rot Disease by the Obligate Predators Bdellovibrio and Like Organisms

“…Consequently, resistant cells of the pathogen may remain, constituting a potential for regrowth and infection. We further examined how resistance is generated, showing that a low concentration of predator and prey (B6:P5 or B6:P6) was not conducive to predation and that low prey concentrations slow predation (31,48). This may explain why, at B6:P5 and B6:P6, the original and final prey populations after incubation with the predator for 5 and 24 h were similar.…”

“…The P. dendritiformis culture was either concentrated or serially diluted to obtain various E. coli:P. dendritiformis ratios upon mixing. Twenty l of the predator, 100 l of the prey, 100 l of P. dendritiformis, and 780 l amended HEPES (25 mM HEPES, 2 mM (31). Three experiments with three replicates were conducted.…”

“…Predation was visually assessed by clarification of the suspension, and confirmed by phase-contrast microscopy, for the presence of a high density of predators (small, rapidly swimming cells) and a low density of prey (larger cells). Furthermore, predation by B. bacteriovorus HD100, 109J, and the ΔmerRNA mutant expressing Td-tomato was tracked by fluorescence (predator growth) and OD (prey decay) in a plate reader (Tecan Spark 10M; Switzerland) (31). Three experiments with three replicates were conducted for each combination of predator and prey in both settings.…”

Predation strategies of the bacterium Bdellovibrio bacteriovorus result in overexploitation and bottlenecks

“…Firstly, natural environments are spatially heterogeneous, facilitating spatial refuges promoting the survival of prey species and by extension the survival of BALOs (19,20,62). Secondly, characteristics of the environment can make predation less efficient (giving prey a greater opportunity to recover) (63)(64)(65)(66). Thirdly, seasonal changes can result in a temporal refuge, with prey concentrations varying with temperature (67,68).…”

The Functional Significance of Bacterial Predators

“…Predators are thought to be functionally significant in microbial food webs, but quantitative estimates in situ have been very difficult to obtain. It is possible to use fluorescent markers and plate counts to estimate growth rates of predators in artificial media ( 12 ), but applying such approaches in the field is challenging. For example, it is known that phages prey upon cyanobacteria in rice paddy soils, but the rates of predation are unknown ( 13 ).…”