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Biosynthesis and Regulation of Two Groups of Antimicrobial Natural Products fromLysobacter
Lysobacter is a genus of Gram-negative bacteria and a new source for bioactive natural products. This dissertation described the studies of two group of antimicrobial natural products from two species of Lysobacter. The discovery of new antibiotics is an urgent and continual need due to the constant emergence of drug-resistant pathogens, and microbial natural products remain the most fruitful source of new antibiotics. In L. antibioticus OH13, we have studied the biosynthetic mechanism for phenazines, a group of tricyclic dibenzopyrazines that exhibit diverse biological activities. Our research focused on new enzymes for the tricycle decorations, as phenazine activities are often dictated by the decorating groups. We demonstrated that LaPhzM encodes a SAM-dependent O-methyltransferase that is responsible for both monomethoxy and dimethoxy formation. We developed one-pot biosynthesis of myxin, a well-known phenazine antibiotic, by in vitro reconstitution. We also determined the X-ray crystal structure of LaPhzM with a bound cofactor at 1.4 Å resolution. Building upon the enzymatic studies, we developed a chemoenzymatic approach toward new phenazine antibiotics. We systematically tested the selectivity of three decorating enzymes, LaPhzS, LaPhzNO1, and LaPhzM, toward a focused library of phenazines. The studies revealed the effects of decorating groups on the activity and selectivity of the enzymes. The chemoenzymatic synthesis also generated several dozens of new phenazines. In L. enzymogenes OH11, we have investigated the biosynthesis and regulation of the antifungal HSAF and analogs, a group of polycyclic tetramate macrolactames that are structurally and mechanistically distinct from the existing antifungal drugs. We found that the chitin polymer of fungal cell walls was used by Lysobacter to promote HSAF production and a lytic polysaccharide monooxygenase (LPMO), LeLPMO10A, plays a crucial role in the chitin-induced HSAF production. LeLPMO10A mutation led to loss of the chitin-induced HSAF production and a decreased interaction between OH11 and fungi. This study identified the first LPMO in Lysobacter and revealed an intriguing strategy utilized by Lysobacter during the interactions with fungi, in which Lysobacter makes a secreted lytic enzyme to cooperate with a group of small molecule antifungal compounds, in order to effectively prey on fungi.
Jiang, Jiasong, "Biosynthesis and Regulation of Two Groups of Antimicrobial Natural Products fromLysobacter" (2019). ETD collection for University of Nebraska - Lincoln. AAI22588269.