Isolation, Genomic Characterization, and Biocontrol Potential of a Drexlerviridae Phage against Environmental Escherichia coli in Wastewater Models.

Background

The persistence of chlorine-tolerant Escherichia coli in wastewater treatment systems, which constitutes a major hazard to public health, highlights the need for alternative biological disinfection methods like phage-based biocontrol. However, relatively few studies have evaluated well-characterized bacteriophages under wastewater conditions that are similar to real-world treatment settings. This study aimed to isolate and characterize a bacteriophage targeting a putative chlorine-tolerant Escherichia coli, and evaluate it under wastewater conditions.

Methods

Bacteriophage infecting an environmental Escherichia coli strain was isolated from wastewater. The phage was characterized via host range, transmission electron microscopy (TEM), thermal and pH stability, chlorine stability, and one-step growth curve dynamics. Whole-genome sequencing was performed for molecular profiling. After thorough biological characterization, the phage was tested in a spiked heat-sterilized wastewater microcosm and in conditions more similar to those found in real wastewater treatment settings.

Results

Phage vB_EcoM_Ww_Az2 infecting a putative chlorine-tolerant Escherichia coli Az_5 was isolated. It was classified within the class Caudoviricetes and the family Drexlerviridae based on genomic and phylogenetic analyses. It exhibited high stability across pH 4-12 and tolerated temperatures up to 55 °C for 15 min. The phage demonstrated an 84% adsorption rate within 15 min, a 30-min latent period, a 15-min rise period, and a burst size of 67 PFU/cell. At an MOI ≥ 5, it completely eliminated E. coli Az_5 within 2 h at 37 °C. In a spiked heat-sterilized wastewater microcosm (MOI = 5), the phage reduced the host population by 5 Log10 units after 12 h. In addition, it decreased total bacterial count, total coliforms, and fecal coliforms by 0.7, 0.6, and 0.28 Log10 units, respectively, in real secondary treated wastewater.

Conclusion

These results offer experimental evidence that using a well-characterized Drexlerviridae phage as a complementary biocontrol agent in real wastewater treatment systems is feasible and promising.