Isolating and Characterizing Predatory Bacteria From The Built Environment
Authors: Zappia Luke Conroy , Williams Laura E. 
Published: November 2023

Predatory bacteria attack and digest other bacteria, including animal and plant pathogens. Bdellovibrio, the most widely studied of predators, attach to Gram‐negative host cells and penetrate the periplasm. The host cell then bursts via predator propagation. A variety of predatory bacteria species have been observed across environments ranging from terrestrial to aqueous. Understanding variation in prey range and predation efficiency could inform development of predatory bacteria as alternatives to antibiotics.

To further explore variation among predatory bacteria, we aimed to isolate and characterize predatory bacteria from the built environment via culture‐independent and dependent approaches. In culture‐independent approaches, we collected swab samples from a janitorial closet drain located at Providence College and extracted metagenomic DNA. Using Bdellovibrio‐specific PCR of the 16S rRNA gene, we assayed the drain samples and detected positive evidence of predatory bacteria. In culture‐dependent approaches, we used Gram‐negative bacteria previously isolated from a freshwater stream (Aeromonas and Raoultella) and a type strain of E. coli as prey to obtain pure predatory bacteria isolates via enrichments and double agar overlay. We observed attachment of predatory bacteria to prey cells via 1000× phase contrast microscopy and monitored changes in OD600 over time. When enrichments were plated via double agar overlay, plaque formation varied in size and appearance. Enrichments using Aeromonas and E. coli each yielded one plaque phenotype. Enrichments using Raoultella produced six plaque phenotypes. This range of plaque phenotypes poses the question of whether these are genetically distinct strains of predatory bacteria or if one strain recovered from the drain is exhibiting phenotypic plasticity.

To address this question, we sequenced the 16S rRNA gene of each of the eight isolates using universal primers targeting bacteria. The resulting ~1300 bp sequence was identical for seven isolates (one isolate is in the process of 16S rRNA gene sequencing). This 16S rRNA gene sequence has 95%–96% identity to Bdellovibrio bacteriovorus, suggesting that these isolates are within the Bdellovibrio genus. Moving forward, we will perform genome sequencing to identify any genotypic differences that may explain the different plaque phenotypes observed. We will also test prey range and predation efficiency using a wide assortment of gram‐negative bacteria. Because the drain environment is ideal for biofilm formation, these predatory bacteria isolates may be adapted to attack prey bacteria in biofilms. Biofilm formation is a major concern in hospital settings, especially regarding formation on indwelling medical devices. This work will contribute to our understanding of predation in bacteria and explore the potential for therapeutic applications of predatory bacteria in the control of pathogens.

Support or Funding Information

Research reported in this poster was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Studies of the National Institutes of Health under grant number 2 P20 GM103430