News and views on protein secretion systems

A High-Throughput Interbacterial Competition Screen Identifies ClpAP in Enhancing Recipient Susceptibility to Type VI Secretion System-Mediated Attack by Agrobacterium tumefaciens

“…This result implies that the process affecting the outcome of A. tumefaciens T6SS killing to E. coli occurs in the cytoplasm, presumably after the injection of the T6SS puncturing apparatus. Previous studies have mainly focused on how attacker T6SS is regulated and sensed (Filloux and Sagfors, 2015;Alteri and Mobley, 2016;Hood et al, 2017). This study provides a new insight that recipient cell genes can also affect the T6SS killing outcome and that it could take place after the injection of the T6SS apparatus into the recipient cytoplasm.…”

“…Among them, the Gramnegative bacteria use a variety of protein secretion systems such as type I secretion system (T1SS) (García-Bayona et al, 2017, type IV secretion system (T4SS) (Souza et al, 2015;Bayer-Santos et al, 2019), contact-dependent inhibition (CDI; belongs to type V secretion system) (Aoki et al, 2005(Aoki et al, , 2010, and type VI secretion system (T6SS) (LeRoux et al, 2012;Basler et al, 2013) as antibacterial weapons. Bacteria that produce and deliver protein toxins, the effectors, through secretion systems to kill other bacteria are attacker cells, and the attacked cells are the recipient cells (Costa et al, 2015;Filloux and Sagfors, 2015). Attacker cells also produce cognate immunity proteins to neutralize effectors to prevent self-intoxication (Alteri and Mobley, 2016;Lien and Lai, 2017).…”

Role of Recipient Susceptibility Factors During Contact-Dependent Interbacterial Competition

“…Bacteria are one of the most abundant forms of life on earth, and they have developed multiple strategies to compete with each other and fight for limited resources and space (Foster and Bell, 2012;Ghoul and Mitri, 2016). An effective strategy in this war game is to deliver toxins into opponents in order to kill them or challenge their fitness (Costa et al, 2015;Filloux and Sagfors, 2015;Green and Mecsas, 2016;Coulthurst, 2019;Klein et al, 2020). These toxins are deadly when they destroy the cell membrane integrity (e.g., peptidoglycan hydrolase, amidase, lipase, or pore-forming protein) or degrade nucleic acid (DNase, RNase, or tRNase) (Willett et al, 2015b;Lien and Lai, 2017).…”

“…There are several protein secretion systems that have been designed by bacteria for robust and efficient delivery of protein from the cytosol across the cell envelope. Among the nine identified so far (reviewed in Filloux and Sagfors, 2015;Christie, 2019), some have a proven capability to deliver antibacterial toxins (Aoki et al, 2005;Hood et al, 2010;Souza et al, 2015;Cao et al, 2016;García-Bayona et al, 2017). These are the type I secretion system (T1SS), type IV secretion system (T4SS), type V secretion system (T5SS) and here more specially those called contact-dependent inhibition (CDI) system, type VI secretion system (T6SS), and type VII secretion system (T7SS) (Figure 1).…”

“…To date, several papers have provided thorough overviews of the molecular mechanisms associated with these secretion systems, such as structural organization, regulatory networks, or the identity and mode of action of a repertoire of antibacterial toxins (Costa et al, 2015;Filloux and Sagfors, 2015;Green and Mecsas, 2016;Coulthurst, 2019;Klein et al, 2020). It is seldom considered what in the recipient cells might be required for an attack to be successful such as recipient susceptibility (RS) factors.…”