Spatiotemporal topography of the BAM complex in relation to peptidoglycan and cell division

Gram-negative bacteria possess a three-layered envelope composed of two concentric membranes, the inner membrane and the outer membrane (OM). In-between an aqueous space called the periplasm that contains the peptidoglycan (PG) layer. The envelope ensures protection against diverse hostile environments and offers an effective barrier against antibiotics.
Bacteria evolved sophisticated machineries that maintain the integrity and functionality of each layer. The β-barrel assembly machinery (BAM), for example, is an essential complex responsible for the insertion of the outer membrane integral proteins.
In immunolabelling Escherichia coli cells, the antibody detection of BAM required the enzymatic digestion of the PG layer, suggesting that spans below the PG, revealing for the first time the spatial arrangement between the OM BAM and the PG layer.
The BAM localizes in foci in the OM, with an accumulation at the division site in constricting cells. When the cell division was impaired at an early stage, the BAM midcell localization was lost, implying a cross-talk between cell division and the BAM complex. These results suggest spatiotemporal coordination with envelope protein machineries.
Lastly, a novel cyan-fluorescent protein was engineered to outstand tightly oxidizing environments, such as the bacterial periplasmic space and the eukaryotic endoplasmic reticulum.