Structure and function analysis of the natural product plantazolicin, a bacillus anthracis-specific antibiotic

Bacteria are a fruitful source of metabolites, many of which have been the scaffolds for the majority of approved antibiotic compounds. In this dissertation, I present the discovery and characterization of a bacterial natural product from Bacillus methylotrophicus FZB42, a Gram-positive, rod-shaped bacterium that stimulates plant growth. A prolific producer of secondary metabolites, FZB42 excretes a compound bearing the molecular mass of 1335 Daltons called plantazolicin (PZN). I describe the genetic locus responsible for the biosynthesis of PZN, which is ribosomally synthesized via an amino acid precursor peptide and post-translationally modified to contain thiazoles and (methyl)oxazoles. This group of compounds, known as thiazole/oxazole-modified microcins (TOMMs), exhibit disparate biological activities and complex chemical structures. Using high-resolution mass spectrometry, chemoselective modification, genetic interruptions, and various spectroscopic tools, I report the molecular structure of PZN. PZN contains two conjugated polyazole moieties and an Nα,Nα-dimethylarginine on the amino terminus. By altering oxygenation levels during fermentation, PZN analogs were produced that bear variability in their heterocycle content, which yielded insight into the order of biosynthetic events. Extensive tailoring of PZN endows it with not only a rigid, polyheterocyclic structure, but also antibacterial activity. After screening numerous microorganisms, PZN exhibited highly selective antibiotic activity against Bacillus anthracis. This remarkably discriminatory activity rivals a previously-described B. anthracis-specific gamma (γ) phage lysis assay in distinguishing B. anthracis from other members of the Bacillus cereus group. I evaluate this unusually selective activity by measuring the RNA expression profile of PZN-treated B. anthracis, which revealed significant upregulation of genes within the cell envelope stress response. Using fluorescence microscopy, PZN localizes to distinct ~200 nm wide foci within the envelope; furthermore, like other cell envelope-acting compounds, PZN depolarizes the B. anthracis membrane. Upon selection and whole-genome sequencing of PZN-resistant mutants of B. anthracis, I implicate a relationship between the action of PZN and the phospholipid cardiolipin within the membrane. Exogenous cardiolipin increases the potency of PZN in wild type B. anthracis and promotes the incorporation of fluorescently tagged PZN in the cell envelope. I propose that PZN localizes to and exacerbates structurally compromised regions of the bacterial membrane, which ultimately results in cell lysis.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Microbiology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2016

Author dc:creator

• Molohon Hess, Katie Jo

Contributors dc:contributor

• Mitchell, Douglas A
• Blanke, Steven R
• Kuzminov, Andrei
• Olsen, Gary J

• Plantazolicin
• Natural product
• Bacillus anthracis
• Mode of action

Statement dc:rights

• Copyright 2015 Katie Molohon Hess

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/89125

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/89125