Role of VapBC4 toxin-antitoxin system ofSulfolobus acidocaldariusin heat stress adaptation
Authors: Bhowmick Arghya , Recalde Alejandra , Bhattacharyya Chandrima , Das Jagriti , Rodriguez-Cruz Ulises E. , Albers Sonja-Verena , Ghosh Abhrajyoti 
Published: June 2024

ABSTRACTToxin-antitoxin (TA) systems are important for stress adaptation in prokaryotes, including persistence, antibiotic resistance, pathogenicity, and biofilm formation. Toxins can cause cell death, reversible growth stasis, and direct inhibition of crucial cellular processes through various mechanisms, while antitoxins neutralize the effects of toxins. In bacteria, these systems have been studied in detail, whereas their function in archaea remains elusive. During heat stress, the thermoacidophilic archaeonSulfolobus acidocaldariusexhibited an increase in the expression of several bicistronic type IIvapBCTA systems, with the highest expression observed in thevapBC4system. In the current study, we performed a comprehensive biochemical characterization of the VapBC4 TA system, establishing it as a bonafide type II toxin-antitoxin system. The VapC4 toxin is shown to have high-temperature catalyzed RNase activity specific for mRNA and rRNA, while the VapB4 antitoxin inhibits the toxic activity of VapC4 by interacting with it. VapC4 toxin expression led to heat-induced persister-like cell formation, allowing the cell to cope with the stress. Furthermore, this study explored the impact ofvapBC4deletion on biofilm formation, whereby deletion ofvapC4led to increased biofilm formation, suggesting its role in regulating biofilm formation. Thus, during heat stress, the liberated VapC4 toxin in cells could potentially signal a preference for persister cell formation over biofilm growth. Thus, our findings shed light on the diverse roles of the VapC4 toxin in inhibiting translation, inducing persister cell formation, and regulating biofilm formation inS. acidocaldarius, enhancing our understanding of TA systems in archaea.IMPORTANCEThis research enhances our knowledge of Toxin-antitoxin (TA) systems in archaea, specifically in the thermoacidophilic archaeonSulfolobus acidocaldarius. TA systems are widespread in both bacterial and archaeal genomes, indicating their evolutionary importance. However, their exact functions in archaeal cellular physiology are still not well understood. This study sheds light on the complex roles of TA systems and their critical involvement in archaeal stress adaptation, including persistence and biofilm formation. By focusing onS. acidocaldarius, which lives in habitats with fluctuating temperatures that can reach up to 90℃, the study reveals the unique challenges and survival mechanisms of this organism. The detailed biochemical analysis of the VapBC4 TA system, and its crucial role during heat stress, provides insights into how extremophiles can survive in harsh conditions. The findings of this study show the various functions of the VapC4 toxin, including inhibiting translation, inducing persister-like cell formation, and regulating biofilm formation. This knowledge improves our understanding of TA systems in thermoacidophiles and has broader implications for understanding how microorganisms adapt to extreme environments.