Control of bacterial cell wall autolysins by peptidoglycan crosslinking mode

To withstand their internal turgor pressure and external threats, most bacteria have a protective peptidoglycan (PG) cell wall. The growth of this PG polymer relies on autolysins, enzymes that create space within the structure. Despite extensive research, the regulatory mechanisms governing these PG-degrading enzymes remain poorly understood. Here, we unveil a novel and widespread control mechanism of lytic transglycosylases (LTs), a type of autolysin responsible for breaking down PG glycan chains. Specifically, we show that LD-crosslinks within the PG sacculus act as an inhibitor of LT activity. Moreover, we demonstrate that this regulation controls the release of immunogenic PG fragments and provides resistance against predatory LTs of both bacterial and viral origin. Our findings address a critical gap in understanding the physiological role of the LD-crosslinking mode in PG homeostasis, highlighting how bacteria can enhance their resilience against environmental threats, including phage attacks, through a single structural PG modification.

We thank all the members of the Cava lab for helpful discussions. Special thanks to Akbar Espaillat for providing the pET28b::slt70Ec and pBAD::ldtE plasmids, Nikola Zlatkov Kolev for providing the lambda phage, Alexander Harms for providing phages P1, P2, T4 and T5, and the Feldman lab for providing the Tse4 effector protein from Acinetobacter baumannii. We thank Michael Gilmore for carefully reading the manuscript. Research in the Cava lab is supported by The Swedish Research Council (VR), The Knut and Alice Wallenberg Foundation (KAW), The Laboratory of Molecular Infection Medicine Sweden (MIMS) and The Kempe Foundation. Work in the Dörr lab is supported by NIH R01GM130971. Open access funding provided by Umea University.

Peer reviewed