Have an Ion on It: The Life‐Cycle of Bdellovibrio bacteriovorus Viewed by Helium‐Ion Microscopy

Abstract

Helium‐ion microscopy (HIM) has so far rarely been employed to image microbial interactions. Here, the visualization of the life‐cycle of the bacterial predator Bdellovibrio bacteriovorus HD100 with Escherichia coli and Pseudomonas putida, respectively, as prey is presented. The predator is brought in contact with prey and samples are taken at selected times. The system is monitored by phase‐contrast microscopy and HIM. For HIM imaging, a sample preparation protocol is established that preserves the structure of Bdellovibrio, prey, and bdelloplasts. The micrographs show the attachment of the predator to its prey, the evolution of bdelloplasts, their lysis, and the release of predator progeny. The combination of HIM with two more approaches allows for investigating predator–prey interactions from different angles: First, phase‐contrast micrographs provide quantitative information for the numbers of predator, prey, and bdelloplasts. Second, a numerical model solving the retarded differential equations that describe the system's time‐evolution is developed and fits the experimentally determined cell numbers. In conclusion, the high resolution, the large depth of focus, and surface sensitivity of HIM hold promise to expand future studies on so far neglected ecological interactions within the microbial food web, in particular in samples with pronounced topography such as bacterial biofilms.

Bio-imaging with the helium-ion microscope: A review

“…HIM imaging has already been used to study numerous microorganisms including bacteria [6,18,19,60,79,80], bacteriophages [17,18,81], yeast [82], protozoa [83][84][85], and microalgae [46]. The highly resolved and contrast-rich views of the tiniest creatures that were obtained in these studies are discussed in the following.…”

“…Bdellovibrio bacteriovorous HD100 with the HIM [19]. At time t = 0 they combined cultures of Bdellovibrio and prey, for example, Escherichia coli, and stopped the experiment by chemical fixation at specific points during incubation.…”

“…In the same study, a larger trench with 13 μm × 5 μm area and several micrometres deep was also milled into an agar substrate with Ne ions, exposing a subsurface bacterial colony. In an another HIM-imaging study on a microbiological sample by Said et al [19], Ne-ion milling was used to make a cross section of a Bdellovibrio-E. coli bdelloblast shortly after lysis (Figure 15b). A porous internal structure was revealed, with Bdellovibrio progeny penetrating the membrane.…”

“…The possibility to image the attachment of bacterial parasites to the outer membranes of bacteria at high resolution in, at least compared to TEM, a relatively natural state makes HIM a very powerful tool for the investigation of living antibiotics. The work on the life cycle of the bacterial predator Bdellovibrio bacteriovorus by Said et al [19] and a study on the pH-responsive encapsulation of bacteriophages for phage therapy by Vinner et al [20] are first examples.…”

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

“…Both models again showed a destabilising effect of nutrient enrichment, albeit somewhat ameliorated by the presence of a decoy species. Similarly, Hobley et al (2006), Baker et al (2017) and Said et al (2019) included a predator-prey complex and a Holling type I functional response. Two further models have been developed by Hol et al (2016) and Dattner et al (2017), both including spatial structure.…”