What lies immediately outside the thin peptidoglycan wall of a Gram-negative bacterium?

1. A Gram-negative wall is only a few layers of peptidoglycan, about 10 percent of the total wall. 2. Surrounding it is an outer envelope containing lipopolysaccharides and lipoproteins. 3. That envelope is sometimes called a second lipid bilayer, although its chemistry differs from a plasma membrane. 4. Teichoic acids are a Gram-positive feature, so they cannot be the outer layer here. 5. Pseudopeptidoglycan is one of the four archaean wall types, not a bacterial layer. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 22 "Prokaryotes: Bacteria and Archaea", section 22.2 Structure of Prokaryotes_