Biology subjects

Santiago, A. G.

Publications and source records attributed to Santiago, A. G..

2 recordsLinked to original sources

bioRxiv2019

The cell cycle in Staphylococcus aureus is regulated by an amidase that controls peptidoglycan synthesis

Bacteria are protected by a polymer of peptidoglycan that serves as an exoskeleton. In Staphylococcus aureus, the enzymes that assemble peptidoglycan move during the cell cycle from the periphery, where they are active during growth, to the division site where they build the partition between daughter cells. But how peptidoglycan synthesis is regulated throughout the cell cycle is not understood. Here we identify a membrane protein complex that spatially regulates S. aureus peptidoglycan synthesis. This complex consists of an amidase that removes peptide chains from uncrosslinked peptidoglycan and a partner protein that controls its activity. Typical amidases act after cell division to hydrolyze peptidoglycan between daughter cells so they can separate. However, we show that this amidase controls cell growth. In its absence, excess peptidoglycan synthesis occurs at the cell periphery, causing cells to grow so large that cell division is defective. We show that cell growth and division defects due to loss of this amidase can be mitigated by attenuating the polymerase activity of the major S. aureus peptidoglycan synthase. Our findings lead to a model wherein the amidase complex regulates the density of peptidoglycan assembly sites to control peptidoglycan synthase activity at a given cellular location. Removal of peptide chains from peptidoglycan at the cell periphery promotes synthase movement to midcell during cell division. This mechanism ensures that cell expansion is properly coordinated with cell division.

microbiology↗

bioRxiv2019

Mechanical stress compromises multicomponent efflux complexes in bacteria

Physical forces have long been recognized for their effects on the growth, morphology, locomotion, and survival of eukaryotic organisms1. Recently, mechanical forces have been shown to regulate processes in bacteria, including cell division2, motility3, virulence4, biofilm initiation5,6, and cell shape7,8, although it remains unclear how mechanical forces in the cell envelope lead to changes in molecular processes. In Gram-negative bacteria, multicomponent protein complexes that form rigid links across the cell envelope directly experience physical forces and mechanical stresses applied to the cell. Here we manipulate tensile and shear mechanical stress in the bacterial cell envelope and use single-molecule tracking to show that shear (but not tensile) stress within the cell envelope promotes disassembly of the tripartite efflux complex CusCBA, a system used by E. coli to resist copper and silver toxicity, thereby making bacteria more susceptible to metal toxicity. These findings provide the first demonstration that mechanical forces, such as those generated during colony overcrowding or bacterial motility through submicron pores, can inhibit the contact and function of multicomponent complexes in bacteria. As multicomponent, trans-envelope efflux complexes in bacteria are involved in many processes including antibiotic resistance9, cell division10, and translocation of outer membrane components11, our findings suggest that the mechanical environment may regulate multiple processes required for bacterial growth and survival.

biophysics↗