## 3 Discussion
Similarly, in our study, we demonstrated that an environment of nutritional starvation induced the expression of the YoeB-YefM and PasT-Pasl systems. Additionally in this condition, there was an induction of only the toxin _yhaV_ in the bacterial stationary growth phase, a fact that was also observed in the comprehensive transcription analysis of the _E. coli_ O157-H7 CcdB-CcdA system under nutritional scarcity [31]. The explanation of chromosomal type II TA system activation in nutritional scarcity might be linked to bacteria undergoing programmed death, i.e., the cell undergoes a state of growth inhibition, enabling a specific number of cells to endure periods of starvation. This state can be reversed upon encountering nutrient-rich conditions again [28]. In our study, the induction of the type II TA systems under examination do not appear to be linked to the oxidative stress response since there was no upregulation in the expression in any of the selected systems. This result is surprising, given that [PERSON] et al. [29] demonstrated that the MazzF system triggered cell death in _E. coli_ under oxidative stress during the logarithmic phase. On the contrary, the _yhaV-prl_F genes were downregulated in oxidative stress conditions, which corroborates with the findings on pathogenic _Klebsiella pneumoniae_, where the TA system MazzF had its gene expression reduced under oxidative stress [32]. Along with the _yhaV-prl_F, we also observed _mazE_and _pas1_ antitoxin downregulation. Frequent upregulation of the toxin in the TA system can impact bacterial virulence. Interestingly, however, the HigA antitoxin within the HigBA TA system in _Pseudomonas aeruginosa_ has been found to impair the expression of different virulence genes [33]. A possible explanation for the singular downregulation of the antitoxins here identified could be an effort of the bacteria to counteract the inhibitory role of antitoxins towards virulence factors produced, especially necessary in the diverse stress conditions that a hybrid _E. coli_ faces within the host. There is still no consensus on whether TA systems are regulated independently or in combination with other regulatory factors. However, some evidence points to the notion that some systems may be activated together, as for the MqsA system that was previously linked to the suppression of _rpoS_. Notably, the MqsA antitoxin has been demonstrated to function as a global transcriptional regulator, suppressing the expression of _rpoS_ and _csgD_ genes that encode pleiotropic regulators involved in stress responses and biofilm formation [15; 34]. In a separate study, [PERSON] et al. [31] demonstrated that _rpoS_ and TA system genes are activated during nutritional stress, coordinating a response that alters metabolic processes and promotes bacterial survival in _E. coli_ O157. The transition from exponential to stationary phase modulates the expression of both _rpoS_ and TA genes, which may be critical for managing nutritional stress and enabling bacteria to adapt and maintain virulence under adverse conditions. Additionally, another study highlights the connection between TA systems and the stringent response, mediated by guanosine pentaphosphate/tetraphosphate [(p)ppGpp], which activates TA systems during nutrient deprivation. This leads to cell growth inhibition and the formation of persister cells [35]. We also explored the association between type II TA systems with the response to osmotic stress, being the only stress factor that led to a system-dependent regulation demonstrated by a significant upregulation of the CcdB-CcdA system transcription but by a downregulation of the YoeB-YefM system. The CcdB toxin targets DNA gyrase, an essential type II topoisomerase in _E. coli_, blocking polymerase passage and leading to double-strand DNA breaks. Consequently, cellular replication is inhibited, SOS response is induced, and cell filamentation occurs, thus leading to cell death. Therefore, this system seems to be involved in osmotic stress observed by correlation with a decrease in CFU [3; 36].