Bdellovibrio and Like Organisms in Untreated Municipal Wastewater: Isolation, Phylogenetic Diversity, and Predatory Activity

Untreated wastewater carries pathogenic and antibiotic-resistant bacteria into the environment, and current treatment processes may not completely remove these bacteria. One possible biological control comes from Bdellovibrio and like organisms (BALOs), predatory bacteria known to prey on Gram-negative bacteria. Here, we isolated, identified, and phylogenetically characterized BALOs from municipal wastewater in Türkiye and examined their predatory potential. Using the double-layer agar plate method, we recovered nine isolates belonging to the genus Bdellovibrio from wastewater samples. We tested their predatory activity against eight Gram-negative bacterial strains, including Escherichia coli and Pseudomonas spp., and scanning electron microscopy (SEM) revealed qualitative differences in biofilm organization and cell-surface morphology following exposure of E. coli ML35 biofilms to the BALO lysate. PCR amplification and 16S rRNA gene sequencing detected a total of 29 BALO sequence records, nine of which were also recovered by culture. Peredibacter-related sequences made up the largest proportion (51.7%), followed by B. bacteriovorus-related sequences (20.7%), Bdellovibrio sp. (20.7%), and BALO-associated sequences with unresolved genus-level affiliation (6.9%). To our knowledge, this is the first report of BALOs isolated from wastewater in Türkiye. Overall, our results show that diverse BALOs occur in municipal wastewater and that several isolates can prey on Gram-negative bacteria associated with wastewater systems.