Microbial metabolites: Structure and function of bacterial siderophores from Pseudomonas species, and, Identification of secondary metabolites excreted by brown rot fungi Gloeophyllum species

Siderophores are high-affinity iron chelators produced by microorganisms for iron uptake. Siderophores can also interact with other metals and participate in metal homeostasis. Pyridine-2,6-bis(thiocarboxylic acid) (pdtc) synthesized by Pseudomonas stutzeri KC as a secondary siderophore is a uniquely multi-potential metabolite, having high affinity for several metals and when complexed with copper, the ability to degrade carbon tetrachloride. These attributes give pdtc a potential for use in metal and organic contaminant remediation.; The primary siderophores of P. stutzeri KC were characterized and a specific siderophore outer membrane receptor identified. Siderophores of fourteen other P. stutzeri and P. balearica strains were also identified to clarify strain KC taxonomy. KC and other related strains were found to produce proferrioxamines, while three remaining strains produced amonabactins, not previously observed in Pseudomonas. A putative ferrioxamine outer membrane receptor gene foxA was identified in strain KC. Genes homologous to foxA were detected in all strains studied. We concluded that P. stutzeri could be divided into two distinct siderotypes; strain KC belongs to the proferrioxamine-producing P. stutzeri.; Investigations of pdtc interactions with toxic metals and metalloids allowed for the elucidation of new pdtc functions in bacterial environment conditioning. Pdtc was shown to reduce selenite and tellurite, forming insoluble selenides and tellurides releasing elemental selenium and tellurium upon hydrolysis. Pdtc was found to reduce chromium(VI) to Cr(III) and form complexes with Cr(III) that hydrolyze, releasing insoluble Cr(III) sulfides. A model of strain KC interactions with chromium was proposed and the chromate transporter chrA described. Pdtc formed poorly soluble complexes with mercury, cadmium, lead, and arsenic(III) that hydrolyzed releasing respective metal sulfides. Strain KC was more tolerant of those metals than the pdtc-negative mutant strain CTN1.; Cu:pdtc is the only metal:pdtc complex that will degrade carbon tetrachloride. Once formed, Cu:pdtc's CCl4 degradation activity is not inhibited by other metals meaning that the chemically synthesized Cu:pdtc may be useful for remediation of CCl4 in mixed metal-organic waste.; Brown-rot fungi excrete various metabolites used in free radical-mediated lignocellulose decomposition. Isocoumarins and phenolic derivatives produced by Gloeophyllum spp. were identified. Our findings contribute to the understanding of wood degradation by brown-rot fungi.