Dominant spoilage bacteria in crayfish alleviate ultrasonic stress through mechanosensitive channels but could not prevent the process of membrane destruction.

Although there have been many studies on the efficacy of ultrasonic inactivation, the stress resistance mechanism of bacteria is still a challenge for complete ultrasonic inactivation. In this study, the dominant spoilage bacteria in crayfish, Shewanella baltica (S. baltica) and Aeromonas veronii (A. veronii), were subjected to high-intensity ultrasonic treatment. The results showed compromised cell membrane, decreased membrane fluidity, hyperpolarized membrane potential, and disrupted succinate-coenzyme Q reductase. Transmission electron microscopy revealed significant fragmentation of S. baltica, whereas A. veronii, with its thick cell wall and outer capsule membrane, demonstrated enhanced resistance to ultrasound. Real-time quantitative PCR indicated that in response to ultrasonic stress, bacteria initiated a stress response mechanism by increasing the expression of mechanosensitive channels; meanwhile, the outer capsule of A. veronii delayed the transformation of ultrasonic external forces into cell membrane stress. The study found that in response to ultrasonic stress, bacteria initiated a stress response mechanism by increasing the expression of mechanosensitive channels as "emergency valve" in short time but could not prevent the process of membrane destruction with prolonged exposure. This finding provided a basis for addressing bacterial stress tolerance in ultrasonic inactivation.