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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

It has been suggested that Escherichia coli can resist aerobic, glucose-starvation conditions by switching rapidly from an aerobic to a fermentative metabolism, thereby preventing the production by the respiratory chain of reactive oxygen species (ROS) that can damage cellular constituents. In contrast, it has been reported that E. coli cannot resist aerobic, phosphate (Pi)-starvation conditions, probably because of the maintenance of an aerobic metabolism and the continuous production of ROS. This paper presents evidence that E. coli cells starved for Pi under aerobic conditions indeed maintain an active aerobic metabolism for about 3 d, which allows the complete degradation of exogenous nutrients such as arginine (metabolized probably to putrescine via the SpeA-initiated pathway) and glucose (metabolized notably to acetate), but cell viability is not significantly affected because of the protection afforded against ROS through the expression of the RpoS and LexA regulons. The involvement of the LexA-controlled RuvAB and RecA proteins with the RecG and RecBCD proteins in metabolism and cell viability implies that DNA double-strand breaks (DSB), and thus hydroxyl radicals that normally generate this type of damage, are produced in Pi-starved cells. It is shown that induction of the LexA regulon, which helps protect Pi-starved cells, is totally prevented by introduction of a recB mutation, which indicates that DSB are actually the main DNA lesion generated in Pi-starved cells. The requirement of RpoS for survival of cells starved for Pi may thus be explained by the role played by various RpoS-controlled gene products such as KatE, KatG and Dps in the protection of DNA against ROS. In the same light, the degradation of arginine and threonine may be accounted for by the synthesis of polyamines (putrescine and spermidine) that protect nucleic acids from ROS. Besides LexA and RpoS, a third global regulator, the nucleoid-associated protein H-NS, is also shown to play a key role in Pi-starved cells. Through a modulation of the metabolism during Pi starvation, H-NS may perform two complementary tasks: it helps maintain a rapid metabolism of glucose and arginine, probably by favouring the activity of aerobic enzymes such as the NAD-dependent pyruvate dehydrogenase complex, and it may enhance the cellular defences against ROS which are then produced by increasing RpoS activity via the synthesis of acetate and presumably homoserine lactone.
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PMID:Role of Escherichia coli RpoS, LexA and H-NS global regulators in metabolism and survival under aerobic, phosphate-starvation conditions. 1043 94

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