Infants are in negative iodine balance on current standard regimens of total parenteral nutrition, with a mean iodine intake of 3 µg/kg/day (150 ml/kg/day). The recommended enteral intake of iodine for preterm infants is 30 µg/kg/day. Gastrointestinal absorption of iodine is high, suggesting that parenteral intakes should approach enteral recommendations. Iodine is essential for synthesis of thyroid hormones, and thyroxine is necessary for brain development. Transient hypothyroxinaemia in preterm infants is characterised by postnatal reductions in serum levels of total thyroxine, free thyroxine, and triiodothyronine, with normal levels of thyroid stimulating hormone. 1Transient hypothyroxinaemia is present in most infants of < 30 weeks gestation and is characteristically associated with reductions in intelligence quotient scores but also increased risks of cerebral palsy.2 The cause of transient hypothyroxinaemia is not clear, with contributions from withdrawal of maternal-placental thyroxine transfer, hypothalamic-pituitary-thyroid immaturity, developmental constraints on the synthesis and peripheral metabolism of iodothyronines, non-thyroidal illness, and iodine deficiency. 3 An enteral intake of at least 30-40 µg iodine/kg/day is required to achieve a positive iodine balance in healthy preterm infants. 4 Younger and sicker infants, 27-30 weeks gestation, can be in negative iodine balance for the first weeks, and 30 µg iodine/kg/day is the recommended enteral intake for extreme preterm infants.3 Increasing enteral intakes further to 40-50 µg iodine/kg/day in more mature preterm infants does not alter serum iodothyronine levels.5 Infants who were parenterally fed were excluded from all these studies. We now report iodine intakes and urinary iodine outputs in a cohort of infants of < 30 weeks gestation who were initially parenterally fed. PATIENTS AND METHODSThirteen consecutive inborn infants were recruited: male/ female ratio, 6:7; gestation mean, 26.8 weeks (range 24-29); birth weight mean, 926 g (range 570-1260). All had intensive care support and survived at least 28 days.On day 1 of life all infants had parenteral dextrose/ electrolyte/amino acid solution (Vaminolact; Fresenius Kabi, Runcorn, Cheshire, UK) with a phosphate supplement (Addiphos; Fresenius Kabi). On day 2, and thereafter, this solution was supplemented with water soluble vitamins (Solvito N; Fresenius Kabi) and trace elements (Peditrace; Fresenius Kabi). In tandem, a fat emulsion (Intralipid 20%; Fresenius Kabi) with added fat soluble vitamins (Vitlipid; Fresenius Kabi) was infused, initially at 8 ml/kg/day, increasing maximally to 18 ml/kg/day by day 5. Enteral feeds were started as hourly boluses, 0.5-1 ml, increased as determined by the infants' clinical condition, with reciprocal reductions in parenteral solutions infused. No infant progressed beyond hourly bolus feeds.A 24 hour iodine balance was calculated for each infant at days 1, 6, 13, and 27. The types and volumes of all enteral and parenteral fluids used were recorded, and the io...

As part of a study of thyroid function in premature babies, the iodine content of their mothers' breast milk, that of 32 formulas from different brands used in Spain, and that of 127 formulas used in other countries was determined. Breast milk contained more iodine -mean (SEM) 10 (1) ,ug/dl -than most of the formulas, especially those for premature babies. Iodine intakes were therefore below the recommended daily amount (RDA) for newborns: babies of 27-30

A Rhizobium etli Tn5 insertion mutant, LM01, was selected for its inability to use glutamine as the sole carbon and nitrogen source. The Tn5 insertion in LM01 was localized to the rsh gene, which encodes a member of the RelA/SpoT family of proteins. The LM01 mutant was affected in the ability to use amino acids and nitrate as nitrogen sources and was unable to accumulate (p)ppGpp when grown under carbon and nitrogen starvation, as opposed to the wild-type strain, which accumulated (p)ppGpp under these conditions. The R. etli rsh gene was found to restore (p)ppGpp accumulation to a ⌬relA ⌬spoT mutant of Escherichia coli. The R. etli Rsh protein consists of 744 amino acids, and the Tn5 insertion in LM01 results in the synthesis of a truncated protein of 329 amino acids; complementation experiments indicate that this truncated protein is still capable of (p)ppGpp hydrolysis. A second rsh mutant of R. etli, strain AC1, was constructed by inserting an ⍀ element at the beginning of the rsh gene, resulting in a null allele. Both AC1 and LM01 were affected in Nod factor production, which was constitutive in both strains, and in nodulation; nodules produced by the rsh mutants in Phaseolus vulgaris were smaller than those produced by the wild-type strain and did not fix nitrogen. In addition, electron microscopy revealed that the mutant bacteroids lacked poly-␤-hydroxybutyrate granules. These results indicate a central role for the stringent response in symbiosis.Rhizobia are soil bacteria able to colonize the roots of compatible legumes under conditions of nitrogen limitation (31,39,46). This symbiotic interaction leads to the formation of organelle-like structures called nodules in the plant roots, in which these bacteria differentiate into N 2 -fixing forms known as bacteroids (31,46). Bacteroids in the nodules are surrounded by the plant cell membrane, called the peribacteroidal membrane (31,42). Bacteroids, the peribacteroidal space, and the peribacteroidal membrane are also referred to as symbiosomes (38). In the process of symbiosome formation, freeliving rhizobia move from a variable environment to a more controlled one inside the plant cells by adapting in succession to three different environments: the rhizosphere, the infection thread (IT), and the plant cell cytoplasm (31, 39, 42). Bacteroid differentiation is accompanied by the loss of bacterial cell division and by a switch from a metabolism dedicated to ammonium assimilation to one dedicated to nitrogen fixation (33, 44).The study of rhizobial metabolic networks that lead to productive nodules is clearly of importance for understanding the symbiotic process. Diverse studies have implicated amino acid metabolism in the bacterial adaptation to nodule conditions, as well as in the metabolic interchange between plant and bacteroids in fully developed nodules (7,16,20,33,34). The rhizobial metabolic adaptations required for using amino acids inside the IT and ammonium excretion in these circumstances could function as a signal to uncouple ammonium assimilation a...

The degradation of asparagine by Rhizobium etli involves asparaginase and aspartate ammonia-lyase (L-aspartase). The two enzymes were shown to be positively regulated by asparagine and negatively regulated by the carbon source. Asparaginase activity was not regulated by oxygen concentration or by nitrogen catabolite repression. Induction of both enzymes by asparagine enables R. etli to utilize asparagine as carbon source. Asparaginase may also be involved in maintaining the optimal balance between asparagine and aspartate. Aspartase was not involved in the utilization of aspartate or glutamate as carbon source. The presence of high levels of the two enzymes in R. etli bacteroids suggests that they may have a role in symbiosis between R. etli and Phaseolus vulgaris.

Rhizobium etli mutants unable to grow on asparagine as the nitrogen and carbon source were isolated. Two kinds of mutants were obtained: AHZ1, with very low levels of aspartase activity, and AHZ7, with low levels of asparaginase and very low levels of aspartase compared to the wild-type strain. R. etli had two asparaginases differentiated by their thermostabilities, electrophoretic mobilities, and modes of regulation. The AHZ mutants nodulated as did the wild-type strain and had nitrogenase levels similar to that of the wild-type strain.Amino acid synthesis has been studied in various microorganisms; amino acid degradation has been less studied, despite the fact that the intracellular amino acid concentration must be the result of its synthesis and degradation. In Neurospora crassa and Rhizobium etli, it has been shown that the intracellular glutamine concentration is the result not only of the regulation of the synthesis but also of the degradation of this amino acid (4, 6-8, 15, 16, 31). To determine if the intracellular concentrations of other amino acids are regulated in the same way as that of glutamine, we decided to study the degradation of asparagine (an amino acid very similar to glutamine, with four carbon skeletons instead of five) in R. etli, a bacterium that establishes symbiosis with Phaseolus vulgaris (39).In R. etli, L-asparagine can be utilized as the sole carbon and nitrogen source through the action of two enzymes (20). The first enzyme, asparaginase (EC 3.5.1.1), catalyzes the hydrolysis of L-asparagine to L-aspartate and ammonium. The second enzyme, L-aspartase (EC 4.3.1.1), catalyzes the reversible deamination of L-aspartate to yield fumarate and ammonium. R. etli asparaginase is found to be positively regulated by its substrate asparagine and negatively regulated by the carbon source; it is not regulated by the amount of oxygen dissolved in the growth medium or by nitrogen catabolite repression, and some asparaginase activity is detected when R. etli is grown on ammonium as a nitrogen source and succinate as a carbon source (20). Asparaginase has been studied in other gramnegative bacteria such as Escherichia coli (10,12,22,24,25,37,47), Salmonella enterica (23), Erwinia chrysanthemi (19), and Vibrio proteus (41) and in gram-positive bacteria such as Bacillus subtilis (1, 21, 43) and Staphylococcus aureus (35,42).R. etli aspartase was found to be positively regulated by asparagine, negatively regulated by the carbon source and by ammonium, and not regulated by the amount of oxygen dissolved in the growth medium (20). L-Aspartase has been studied in other bacteria such as E. coli (25,27,33,36), B. subtilis (43), Pseudomonas fluorescens (30, 45), and Serratia marcescens (44).In this report, we describe the isolation and characterization of R. etli mutants altered in the degradation of asparagine, present evidence that R. etli has two asparaginases, and investigate the regulation of these isoenzymes. The cloning of an R. etli DNA fragment that complements the isolated mutants is also reported...