Pantoea ananatis, a gram-negative bacterium belonging to the Erwiniaceae family, is a well-known phytopathogen isolated from many ecological niches and plant hosts. However, this bacterium also provides us with various beneficial characteristics, such as the growth promotion of their host plants and increased crop yield. Some isolated non-pathogenic strains are promising for the microbial production of useful substances. P. ananatis AJ13355 was isolated as an acidophilic bacterium and was used as an excellent host to produce L-glutamic acid under acidic conditions. The genome sequence of P. ananatis AJ13355 was determined, and specific genome-engineering technologies were developed. As a result, P. ananatis was successfully used to construct a bacterial strain that produces cysteine, a sulfur-containing amino acid that has been difficult to produce through fermentation because of complex regulation. Furthermore, by heterologous expression including plant-derived genes, construction of a strain that produces isoprenoids such as isoprene and linalool as secondary metabolites was achieved. P. ananatis is shown to be a useful host for the production of secondary metabolites, as well as amino acids, and is expected to be used as a platform for microbial production of bioactive substances, aromatic substances, and other high-value-added substances of plant origin in the future.

Pantoea ananatis is a plant pathogen that causes center rot disease in onion. Lipopolysaccharide (LPS), a fundamental constituent of the outer membrane of Gram-negative bacteria, is instrumental in bacterial virulence. This study investigated the role of LPS in P. ananatis by analyzing the LPS biosynthesis-related genes, galU, ugd, waaC, waaG, and waaL. Deletion of each gene impaired LPS biosynthesis and reduced virulence. To understand the basis of this reduced virulence, we examined the deletion mutant phenotypes. Deletion of galU, ugd, waaC, or waaG reduced resistance to polymyxin B and sodium dodecyl sulfate, whereas deletion of waaL reduced resistance only to polymyxin B. All deletion mutants exhibited suppressed flagellar formation, decreased motility, and increased stress-response regulator gene rpoE expression. Furthermore, deletion of galU or waaC reduced pantaphos biosynthesis, a major pathogenicity factor in P. ananatis, and decreased the expression of the pantaphos biosynthetic gene hvrA. These findings indicate that galU, ugd, waaC, waaG, and waaL, through their roles in LPS formation, are required for the virulence of P. ananatis by influencing drug resistance, flagellar motility, and, in part, pantaphos biosynthesis.