The Gram negative bacterial envelope consists on a thin layer of peptidoglycan (cell wall) between the cell membrane and an asymmetric outer membrane (OM), enabling cells to prevent bursting open due to their turgor. During cell division, bacteria produce a peptidoglycan septum at midcell, which must be cleaved for daughter cells to separate. In addition, bacteria must grow their OM by transporting beta barrel proteins and lipoproteins from the cytoplasm and inserting them using a specialized machinery called the BAM complex. In the first part, I will report the identification of a new enzyme, SddA, that modifies a particular type of peptidoglycan material, denuded glycan chains released during the splitting of septal peptidoglycan for daughter cell separation, in the Gram-negative Escherichia coli. We propose a model in which SddA modulates a switch in the septal peptidoglycan splitting, ensuring splitting is activated from the cell membrane in the early stages of cell division and from the outer membrane in the late stages. In the second part, I will describe the newly resolved structure of the BAM complex machinery in the prominent member of the gut microbiome Bacteroides thetaiotaomicron. This new structure is remarkably different from the most studied BAM complex of E. coli, with a large extracellular extension. I will discuss its significance for B. thetaiotaomicron biology and our plans to study its activity and function.