Genome Sequence of Pseudomonas chlororaphis Lzh-T5, a Plant Growth-Promoting Rhizobacterium with Antimicrobial Activity

Biosynthesis and genetic engineering of phenazine-1-carboxylic acid in Pseudomonas chlororaphis Lzh-T5

Phenazine-1-carboxylic acid (PCA) is a biologically active substance with the ability to prevent and control crop diseases. It was certified as a pesticide by the Ministry of Agriculture of China in 2011 and was named "Shenzimycin." Lzh-T5 is a Pseudomonas chlororaphis strain found in the rhizosphere of tomatoes. This strain can produce only 230 mg/L of PCA. We used LDA-4, which produces the phenazine synthetic intermediate trans-2,3-dihydro-3-hydroxyanthranilic acid in high amounts, as the starting strain. By restoring phzF and knocking out phzO, we achieved PCA accumulation. Moreover, PCA production was enhanced after knocking out negative regulators, enhancing the shikimate pathway, and performing fed-batch fermentation, thus resulting in the production of 10,653 mg/L of PCA. It suggested that P. chlororaphis Lzh-T5 has the potential to become an efficiency cell factory of biologically active substances.

Genetic engineering of Pseudomonas chlororaphis Lzh-T5 to enhance production of trans-2,3-dihydro-3-hydroxyanthranilic acid

Trans-2,3-dihydro-3-hydroxyanthranilic acid (DHHA) is a cyclic β-amino acid used for the synthesis of non-natural peptides and chiral materials. And it is an intermediate product of phenazine production in Pseudomonas spp. Lzh-T5 is a P. chlororaphis strain isolated from tomato rhizosphere found in China. It can synthesize three antifungal phenazine compounds. Disruption the phzF gene of P. chlororaphis Lzh-T5 results in DHHA accumulation. Several strategies were used to improve production of DHHA: enhancing the shikimate pathway by overexpression, knocking out negative regulatory genes, and adding metal ions to the medium. In this study, three regulatory genes (psrA, pykF, and rpeA) were disrupted in the genome of P. chlororaphis Lzh-T5, yielding 5.52 g/L of DHHA. When six key genes selected from the shikimate, pentose phosphate, and gluconeogenesis pathways were overexpressed, the yield of DHHA increased to 7.89 g/L. Lastly, a different concentration of Fe3+ was added to the medium for DHHA fermentation. This genetically engineered strain increased the DHHA production to 10.45 g/L. According to our result, P. chlororaphis Lzh-T5 could be modified as a microbial factory to produce DHHA. This study laid a good foundation for the future industrial production and application of DHHA.