Upscaling the production of Bdellovibrio bacteriovorus using metabolically active and heat-inactivated Escherichia coli

Abstract The study aimed to investigate the upscaled culture-based production of the predatory bacterium, Bdellovibrio bacteriovorus ( B. bacteriovorus ) PF13 (isolated from wastewater) using metabolically active and heat-inactivated Escherichia coli ( E. coli ) ATCC 417373 as prey. This approach was used to assess whether heat-treated prey cells could support the production of predatory stock lysates. Heat-inactivation was validated using resazurin assays, which showed reduced relative fluorescence units (RFU) in all heat-treated, E. coli ATCC 417373 samples in comparison to the untreated controls, with the 65 °C treatment yielding the lowest RFU. The predatory lysate was then upscaled, using suspensions of either metabolically active or heat-inactivated (65 °C) E. coli ATCC 417373, from 100 mL to 1 L, and finally to 2.5 L. For the 100 mL, 1 L and 2.5 L co-cultures, using B. bacteriovorus PF13 and metabolically active E. coli ATCC 417373, the PFU/mL and cells/mL of B. bacteriovorus PF13 increased by 2.84 and 1.12 logs, 1.40 and 0.86 logs, and 2.37 and 0.80 logs, respectively. For the 100 mL, 1 L and 2.5 L co-cultures, using B. bacteriovorus PF13 and heat-inactivated E. coli ATCC 417373, the cells/mL of B. bacteriovorus PF13 then increased by 1.27 logs, 1.23 logs, and 0.29 logs, respectively. While further optimisation is required to produce predatory lysates in shorter incubation time periods, this study demonstrated the feasibility of upscaling B. bacteriovorus production using heat-inactivated prey and culture-based methods. This strategy may potentially circumvent the need for bioreactor infrastructure, which is particularly crucial for laboratories in resource-limited countries.