The dark-green pigmented marine bacterium Pseudoalteromonas tunicata produces several extracellular compounds against a range of common fouling organisms including bacteria, fungi, protozoa, diatoms, invertebrate larvae and algal spores. The regulator WmpR, which has N-terminal similarity to ToxR from Vibrio cholerae and CadC from Escherichia coli, controls all of the pigment and antifouling phenotypes. These compounds appear at the onset of stationary phase. The role of WmpR as a stationary phase regulator in P. tunicata was investigated in this thesis. Starvation and stress studies demonstrated that WmpR does not appear to control genes necessary for survival during carbon, phosphate or nitrogen starvation and UV/hydrogen peroxide stress. Intriguingly, phosphate starvation caused pigmentation of wmpR mutant (D2W2) logarithmic phase cells, suggesting a second regulation of the pigments (and thus antifouling compounds) that could be mediated by the PhoR/B twocomponent regulatory system. Proteomic analysis using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) found that 11 proteins were differentially regulated by WmpR, and the identities of some of these proteins suggested a role for WmpR as a general stationary phase regulator rather than a specific starvation or stress regulator. Gene expression studies using RNA-arbitrarily primed PCR introduced a new role for WmpR as a regulator of iron acquisition; a TonB-dependant outer membrane receptor gene and a non-ribosomal peptide synthetase (NRPS) gene were up-regulated in the stationary phase Wt strain compared to the D2W2 strain. An assay for iron-binding activity supported the proposal that the NRPS may be making a siderophore. Further studies demonstrated that WmpR is required for survival under long-term low-iron conditions and that the pigments and antifouling genes are down-regulated during low-iron, while biofilm formation is up-regulated. WmpR also appears to constitutively regulate the production of iron-binding compounds, a novel regulation of iron acquisition that has not been seen in other organisms studied so far. A model is proposed that describes WmpR as responding to environmental signals, including iron, and co-ordinating the expression of a complex regulon including a number of genes involved in iron acquisition, general stationary phase physiology and bioactive secondary metabolite production.
| Identifer | oai:union.ndltd.org:ADTP/215543 |
| Date | January 2006 |
| Creators | Stelzer, Sacha, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Biotechnology and Biomolecular Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Sacha Stelzer, http://unsworks.unsw.edu.au/copyright |
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