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Query: UMLS:C0038187 (starvation)
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Polyamines play an important and central role in normal cell growth and differentiation in many cells. In trypanosomatids, spermidine is also an essential precursor in the biosynthesis of the unique glutathione-spermidine conjugate, trypanothione. Our previous study has shown that the epimastigote stage of Trypanosoma cruzi (Silvio strain) is incapable of significant de novo synthesis of putrescine or cadaverine from their amino acid precursors [Hunter, Le Quesne and Fairlamb (1994) Eur. J. Biochem. 226, 1019-1027]. In this study we show that when grown to late log phase in medium containing trace amounts of putrescine (0.22 microM) and spermidine (0.63 microM), Y-strain epimastigotes contain low levels of polyamines with free glutathione as their principal low molecular mass thiol (> 97% of total glutathione). Following passage into fresh medium, trypanothione and glutathionylspermidine content increase to 46% of total glutathione by mid log phase but returns to less than 3% by late log phase. In contrast, when supplemented at inoculation with exogenous putrescine, glutathione-spermidine conjugates reach 80% of total glutathione by early log phase and remain elevated throughout growth. Supplementation with exogenous putrescine or spermidine during polyamine starvation (late log phase) results in increased conjugate levels (> 74% of total glutathione) and is associated with large increases in total putrescine and spermidine. Likewise, supplementation with exogenous cadaverine and aminopropylcadaverine results in similar increases in trypanothione analogues and total cadaverine and aminopropylcadaverine. In contrast, ornithine, arginine, lysine, agmatine and other amino acid precursors have no effect on polyamine or conjugate levels. No significant ornithine or arginine decarboxylase activities could be detected (< 0.8 pmol min-1 [mg protein]-1). Similar results were obtained for epimastigotes representing all the major zymodeme classes, providing evidence that diamine auxotrophy may be a universal feature of this stage of the life-cycle.
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PMID:Diamine auxotrophy may be a universal feature of Trypanosoma cruzi epimastigotes. 904 26

The siderophore synthetic system in Shewanella species is able to synthesize dozens of macrocyclic siderophores in vitro with synthetic precursors. In vivo, however, although three siderophores are produced naturally in Shewanella algae B516, which carries a lysine decarboxylase (AvbA) specific for siderophore synthesis, only one siderophore can be detected from many other Shewanella species. In this study, we examined a siderophore-overproducing mutant of Shewanella oneidensis which lacks an AvbA counterpart, and we found that it can also produce these three siderophores. We identified both SpeC and SpeF as promiscuous decarboxylases for both lysine and ornithine to synthesize the siderophore precursors cadaverine and putrescine, respectively. Intriguingly, putrescine is mainly synthesized from arginine through an arginine decarboxylation pathway in a constitutive manner, not liable to the concentrations of iron and siderophores. Our results provide further evidence that the substrate availability plays a determining role in siderophore production. Furthermore, we provide evidence to suggest that under iron starvation conditions, cells allocate more putrescine for siderophore biosynthesis by downregulating the expression of the enzyme that transforms putrescine into spermidine. Overall, this study provides another example of the great flexibility of bacterial metabolism that is honed by evolution to better fit living environments of these bacteria.IMPORTANCE The simultaneous production of multiple siderophores is considered a general strategy for microorganisms to rapidly adapt to their ever-changing environments. In this study, we show that some Shewanella spp. may downscale their capability for siderophore synthesis to facilitate adaptation. Although S. oneidensis lacks an enzyme specifically synthesizing cadaverine, it can produce it by using promiscuous ornithine decarboxylases. Despite this ability, this bacterium predominately produces the primary siderophore while restraining the production of secondary siderophores by regulating substrate availability. In addition to using the arginine decarboxylase (ADC) pathway for putrescine synthesis, cells optimize the putrescine pool for siderophore production. Our work provides an insight into the coordinated synthesis of multiple siderophores by harnessing promiscuous enzymes in bacteria and underscores the importance of substrate pools for the biosynthesis of natural products.
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PMID:Promiscuous Enzymes Cause Biosynthesis of Diverse Siderophores in Shewanella oneidensis. 3274 3