Minicells from Highly Genome Reduced Escherichia coli: Cytoplasmic and Surface Expression of Recombinant Proteins and Incorporation in the Minicells

Minicells, small cells lacking a chromosome, produced by bacteria with mutated min genes, which control cell division septum placement, have many potential uses. Minicells have contributed to basic bacterial physiology studies and can enable new biotechnological applications, including drug delivery and vaccines. Genome-reduced (GR) bacteria are another informative area of investigation. Investigators identified that with even almost 30% of the E. coli genome deleted, the bacteria still live. In biotechnology and synthetic biology, GR bacteria offer certain advantages. With GR bacteria, more recombinant genes can be placed into GR chromosomes and fewer cell resources are devoted to purposes apart from biotechnological goals. Here, we show that these two technologies can be combined: min mutants can be made in GR E. coli. The minCminD mutant GR E. coli produce minicells that concentrate engineered recombinant proteins within these spherical delivery systems. We expressed recombinant GFP protein in the cytoplasm of GR bacteria and showed that it is concentrated within the minicells. We also expressed proteins on the surfaces of minicells made from GR bacteria using a recombinant Gram-negative AIDA-I autotransporter expression cassette. As some autotransporters, like AIDA-I, are concentrated at the bacterial poles, where minicells bud, and because the surface-to-volume ratio of the small minicells is higher than bacteria, recombinant proteins expressed on surfaces of the GR bacteria are concentrated on the minicells. Minicells made from GR bacteria can enable useful biotechnological innovations, such as drug delivery vehicles and vaccine immunogens.