Efficacy of sugar excipients on lyophilized C22 phage infectivity evaluated by atomic force microscopy

Abstract

Bacteriophages (phages) show immense potential as biological control agents of pathogenic bacteria in crops. However, their utilization is hindered by the challenges in storage and handling in remote farming areas. Lyophilization has been used to convert phages from solution to powdery form to overcome such issues. In this work, we lyophilized the C22 phage, a promising biocontrol agent of Ralstonia solanacearum causing wilt disease. Sugar excipients were added during the lyophilization step to preserve phage infectivity. We found that 0.5 M sucrose, 0.25 M, and 0.5 M trehalose could retain infectivity of lyophilized C22 phage for ≥ 45% after 90–day storage. Using atomic force microscopy-based imaging, we revealed that both sugars induced aggregation of C22 phage particles. We suggest that aggregation may be a mechanism that prevents phage from degradation since it reduces overall surface that can unfavorably interact with external damaging factors. An insight into phage aggregation can be essential for phage storage and utilization in biocontrol applications.