Kumaran S. Ramamurthi

Ancient mechanics: Bacterial MAIN domains reveal an evolutionary link to eukaryotic mechanotransduction.

A lipid cue drives the subcellular localization of a self-inserting bacterial transmembrane protein.

The correct subcellular localization of proteins is a critical step underlying myriad biological processes, but the cues that drive the specific localization of integral membrane proteins in bacteria remain largely undeciphered. During sporulation in Bacillus subtilis, a rod-shaped outer "mother cell" constructs an internal spherical "forespore" cell that eventually matures into the spore. The integral membrane protein ShfA is made in the mother cell cytosol and localizes to the surface of the forespore. Here, we report that, despite being a multipass transmembrane protein, ShfA spontaneously inserts into the lipid bilayer via its N-terminal "YabQ" domain without the apparent need for a prelocalized insertase. ShfA preferentially inserts into cell division septa in multiple bacterial species, indicating that a widely conserved septal cue drives ShfA localization. Structural modeling suggested that the YabQ domain harbors a specific intramembrane groove that can bind the universal lipid carrier undecaprenyl phosphate (UndP), and in vitro experiments confirmed that ShfA binds to UndP directly. Moreover, UndP depletion in vivo disrupted proper ShfA localization. We propose that ShfA localizes to sites of active cell wall synthesis by binding to UndP and/or molecules like lipid I and lipid II that contain UndP and speculate that the function of ShfA is to stabilize these precursors of cell wall biogenesis from the harsh cytosolic nanoenvironment that surrounds the forespore during sporulation.

A metabolite morphogen coordinates multicellular development in Bacillus subtilis

The transition from unicellular to multicellular growth requires diversification of cellular functions within genetically identical populations. In Bacillus subtilis, biofilm formation is historically viewed as a developmental precursor to sporulation along a linear pathway. Here, we show that biofilm formation and sporulation instead diverge along a branched pathway. A subpopulation that first initiates sporulation catabolizes lipoteichoic acid through the sequential action of the enzymes ShfP (Sporulation heterogeneity factor Poison) and PhoA (alkaline phosphatase A), leading to the release of millimolar concentrations of glycerol. This glycerol impedes sporulation by disrupting cell wall synthesis and cytoplasmic pH, necessitating counteraction by another protein, ShfA (Sporulation heterogeneity factor Antidote). The extracellular glycerol, however, acts as a morphogen that directs neighboring cells to initiate biofilm formation, which we directly visualize in developing populations of cells. Thus, B. subtilis multicellularity emerges through a branched developmental program in which sporulating cells generate the cue that creates the biofilm-producing lineage via cell-cell communication through repurposing of a canonical intracellular metabolite.

16S ribosomal RNA modification drives transcript-specific translation efficiency.

It is proposed that MraW modification of 16S rRNA enhances translation efficiency in general, and that specific transcripts have evolved structural features that fine-tune protein levels that may be prevalent in bacteria which exhibit uncoupled transcription and translation.