The disclosure is in the technical field of synthetic biology and metabolic engineering. The disclosure provides engineered viable bacteria. In particular, the disclosure provides viable bacteria with mutated outer membrane biosynthetic pathway leading to disruption of the pathway, preferably substantially lacking lipopolysaccharide (LPS, endotoxin) within the outer membrane. The disclosure further provides methods of generating viable bacteria and uses thereof. The disclosure also provides compositions and methods for inducing immune responses and for researching and developing therapeutic agents. Furthermore, the disclosure is in the technical field of fermentation of metabolically engineered microorganisms producing bioproduct or metabolite.