Impact of pregnancy planning and preconceptual dietary training on metabolic control and offspring's outcome in phenylketonuria.

To prevent maternal phenylketonuria (PKU) syndrome low phenylalanine concentrations (target range, 120-360 µmol/L) during pregnancy are recommended for women with PKU. We evaluated the feasibility and effectiveness of current recommendations and identified factors influencing maternal metabolic control and children's outcome. Retrospective study of first successfully completed pregnancies of 85 women with PKU from 12 German centers using historical data and interviews with the women. Children's outcome was evaluated by standardized IQ tests and parental rating of child behavior. Seventy-four percent (63/85) of women started treatment before conception, 64% (54/85) reached the phenylalanine target range before conception. Pregnancy planning resulted in earlier achievement of the phenylalanine target (18 weeks before conception planned vs. 11 weeks of gestation unplanned, p < 0.001) and lower plasma phenylalanine concentrations during pregnancy, particularly in the first trimester (0-7 weeks of gestation: 247 µmol/L planned vs. 467 µmol/L unplanned, p < 0.0001; 8-12 weeks of gestation: 235 µmol/L planned vs. 414 µmol/L unplanned, p < 0.001). Preconceptual dietary training increased the success rate of achieving the phenylalanine target before conception compared to women without training (19 weeks before conception vs. 9 weeks of gestation, p < 0.001). The majority (93%) of children had normal IQ (mean 103, median age 7.3 years); however, IQ decreased with increasing phenylalanine concentration during pregnancy. Good metabolic control during pregnancy is the prerequisite to prevent maternal PKU syndrome in the offspring. This can be achieved by timely provision of detailed information, preconceptual dietary training, and careful planning of pregnancy.

Galactokinase deficiency: lessons from the GalNet registry.

PURPOSE: Galactokinase (GALK1) deficiency is a rare hereditary galactose metabolism disorder. Beyond cataract, the phenotypic spectrum is questionable. Data from affected patients included in the Galactosemias Network registry were collected to better characterize the phenotype. METHODS: Observational study collecting medical data of 53 not previously reported GALK1 deficient patients from 17 centers in 11 countries from December 2014 to April 2020. RESULTS: Neonatal or childhood cataract was reported in 15 and 4 patients respectively. The occurrence of neonatal hypoglycemia and infection were comparable with the general population, whereas bleeding diathesis (8.1% versus 2.17-5.9%) and encephalopathy (3.9% versus 0.3%) were reported more often. Elevated transaminases were seen in 25.5%. Cognitive delay was reported in 5 patients. Urinary galactitol was elevated in all patients at diagnosis; five showed unexpected Gal-1-P increase. Most patients showed enzyme activities ≤1%. Eleven different genotypes were described, including six unpublished variants. The majority was homozygous for NM_000154.1:c.82C>A (p.Pro28Thr). Thirty-five patients were diagnosed following newborn screening, which was clearly beneficial. CONCLUSION: The phenotype of GALK1 deficiency may include neonatal elevation of transaminases, bleeding diathesis, and encephalopathy in addition to cataract. Potential complications beyond the neonatal period are not systematically surveyed and a better delineation is needed.

Dietary lipids in glycogen storage disease type III: A systematic literature study, case studies, and future recommendations.

A potential role of dietary lipids in the management of hepatic glycogen storage diseases (GSDs) has been proposed, but no consensus on management guidelines exists. The aim of this study was to describe current experiences with dietary lipid manipulations in hepatic GSD patients. An international study was set up to identify published and unpublished cases describing hepatic GSD patients with a dietary lipid manipulation. A literature search was performed according to the Cochrane Collaboration methodology through PubMed and EMBASE (up to December 2018). All delegates who attended the dietetics session at the IGSD2017, Groningen were invited to share unpublished cases. Due to multiple biases, only data on GSDIII were presented. A total of 28 cases with GSDIII and a dietary lipid manipulation were identified. Main indications were cardiomyopathy and/or myopathy. A high fat diet was the most common dietary lipid manipulation. A decline in creatine kinase concentrations (n = 19, P < .001) and a decrease in cardiac hypertrophy in paediatric GSDIIIa patients (n = 7, P < .01) were observed after the introduction with a high fat diet. This study presents an international cohort of GSDIII patients with different dietary lipid manipulations. High fat diet may be beneficial in paediatric GSDIIIa patients with cardiac hypertrophy, but careful long-term monitoring for potential complications is warranted, such as growth restriction, liver inflammation, and hepatocellular carcinoma development.

Hepatorenal Tyrosinaemia: Impact of a Simplified Diet on Metabolic Control and Clinical Outcome.

Background: Tyrosinaemia type 1 is a rare inherited metabolic disease caused by an enzyme defect in the tyrosine degradation pathway. It is treated using nitisinone and a low-protein diet. In a workshop in 2013, a group of nutritional specialists from Germany, Switzerland and Austria agreed to advocate a simplified low-protein diet and to allow more natural protein intake in patients with tyrosinaemia type 1. This retrospective study evaluates the recommendations made at different treatment centers and their impact on clinical symptoms and metabolic control. Methods: For this multicenter study, questionnaires were sent to nine participating treatment centers to collect data on the general therapeutic approach and data of 47 individual patients treated by those centers. Results: Dietary simplification allocating food to 3 categories led to increased tyrosine and phenylalanine blood concentrations without weighing food. Phenylalanine levels were significantly higher in comparison to a strict dietary regimen whereas tyrosine levels in plasma did not change. Non-inferiority was shown for the simplification and liberalization of the diet. Compliance with dietary recommendations was higher using the simplified diet in comparison to the stricter approach. Age correlates negatively with compliance. Conclusions: Simplification of the diet with increased natural protein intake based on three categories of food may be implemented in the diet of patients with tyrosinaemia type 1 without significantly altering metabolic control. Patient compliance is strongly influencing tyrosine blood concentrations. A subsequent prospective study with a larger sample size is necessary to get a better insight into the effect of dietary recommendations on metabolic control.

Dietary practices in methylmalonic acidaemia: a European survey.

Background The dietary management of methylmalonic acidaemia (MMA) is a low-protein diet providing sufficient energy to avoid catabolism and to limit production of methylmalonic acid. The goal is to achieve normal growth, good nutritional status and the maintenance of metabolic stability. Aim To describe the dietary management of patients with MMA across Europe. Methods A cross-sectional questionnaire was sent to European colleagues managing inherited metabolic disorders (IMDs) (n=53) with 27 questions about the nutritional management of organic acidaemias. Data were analysed by different age ranges (0-6 months; 7-12 months; 1-10 years; 11-16 years; >16 years). Results Questionnaires were returned from 53 centres. Twenty-five centres cared for 80 patients with MMA vitamin B12 responsive (MMAB12r) and 43 centres managed 215 patients with MMA vitamin B12 non-responsive (MMAB12nr). For MMAB12r patients, 44% of centres (n=11/25) prescribed natural protein below the World Health Organization/Food and Agriculture Organization/United Nations University (WHO/FAO/UNU) 2007 safe levels of protein intake in at least one age range. Precursor-free amino acids (PFAA) were prescribed by 40% of centres (10/25) caring for 36% (29/80) of all the patients. For MMAB12nr patients, 72% of centres (n=31/43) prescribed natural protein below the safe levels of protein intake (WHO/FAO/UNU 2007) in at least one age range. PFAA were prescribed by 77% of centres (n=33/43) managing 81% (n=174/215) of patients. In MMAB12nr patients, 90 (42%) required tube feeding: 25 via a nasogastric tube and 65 via a gastrostomy. Conclusions A high percentage of centres used PFAA in MMA patients together with a protein prescription that provided less than the safe levels of natural protein intake. However, there was inconsistent practices across Europe. Long-term efficacy studies are needed to study patient outcome when using PFAA with different severities of natural protein restrictions in patients with MMA to guide future practice.

Dietary Considerations in Tyrosinemia Type I.

Since the introduction of 2-(2 nitro-4-3 trifluoro-methylbenzoyl)-1, 3-cyclohexanedione (NTBC), life expectancy of HT1 patients greatly improved. However, due to treatment with NTBC, tyrosine concentrations greatly increase. As a consequence to possible neurocognitive problems, the main objective of dietary therapy in HT1 is to provide adequate nutrition allowing normal growth and development while strictly controlling tyrosine levels in blood (and tissues). Although no well-defined target levels exist, tyrosine concentrations below 400 µmol/L are considered to be safe. To achieve this aim a diet restricted in natural protein and supplemented with a special tyrosine and phenylalanine-free amino acid mixture is necessary.Dietary management could be strenuous at diagnosis due to several different problems. If vomiting and diarrhea are a major issue at diagnosis, frequent feeding with additional energy from low protein food is needed for catch-up growth. Initiation of dietary treatment is usually easier if diagnosis is directly after birth. Based on newborn screening when infants are still reasonable healthy. If presenting clinically infants may experience serious difficulties in taking the amino acid mixtures probably due to feeding problems while when presenting after some 2-3 months taste development and the difference in the taste of amino acid mixtures compared to regular formula and breast milk increase difficulties with the treatment.Following a dietary treatment is even harder than taking some medicine. Older children and adolescents often relax the diet and at some age become reluctant to stick to a strict regimen. Therefore, adequate training and information should be given to the patients and the family at regular intervals. To achieve this, a multidisciplinary approach involving pediatricians/physicians, dieticians, psychologists and social workers is an asset for the care of patients with HT1.

Control of the Oscillatory Interlayer Exchange Interaction with Terahertz Radiation.

The oscillatory interlayer exchange interaction between two magnetic layers separated by a metallic spacer is one of the few coherent quantum phenomena that persists at room temperature. Here, we show that this interaction can be controlled dynamically by illuminating the sample (e.g., a spin valve) with radiation in the 10-100 THz range. We predict that the exchange interaction can be changed from ferromagnetic to antiferromagnetic (and vice versa) by tuning the amplitude and/or the frequency of the radiation. Our chief theoretical result is an expression that relates the dynamical exchange interaction to the static one that has already been extensively measured.

Effect of dietary regime on metabolic control in phenylketonuria: Is exact calculation of phenylalanine intake really necessary?

BACKGROUND: A phenylalanine (Phe) restricted dietary management is required in phenylketonuria (PKU) to maintain good metabolic control. Nevertheless, five different models of dietary regimes, which differ in their accuracy of Phe documentation, are used. To investigate the effect of the dietary regime on metabolic control, a multicenter evaluation was performed. PATIENTS/METHODS: 149 patients (max. 800 mg Phe-intake/day; 108 children aged 1-9 years and 41 adolescents aged 10-15 years) could be included. They were separated according to age and dietary regime, revealed by a questionnaire on dietary habits. Dietary regimes vary from daily strict calculation of all Phe-intake (group 1) to a rather loose regime only estimating Phe-intake and including high protein food (group 5). Data were analyzed with respect to metabolic control (Phe-concentrations, Phe-concentrations above upper recommended limit during 6 months before the interview), Phe-intake (mg/day) and age (years). RESULTS: Median Phe-concentrations in children did not differ significantly among diet groups (group 1: 161; 2: 229, 3: 236, 4: 249, 5: 288 µmol/l, p = 0.175). However, exact daily Phe calculation led to significantly lower percentage of Phe concentrations above the upper recommended limit (group 1: 17, 2: 50, 3: 42, 4: 50, 5: 75%, p = 0.035). All included patients showed good to acceptable metabolic control. Patients on the dietary regime with the least accuracy, consuming also high protein foods, showed the poorest metabolic control. Median Phe concentrations of all other groups remained within recommended ranges, including from groups not calculating special low protein foods, fruit and vegetables and using a simplified system of recording Phe-intake. In adolescents no significant differences among diet groups were revealed. CONCLUSION: Exact calculation of Phe content of all food is not necessary to achieve good metabolic control in children and adolescents with PKU. Excluding special low protein food, as well as fruit and vegetables from calculation of Phe-intake has no impact on metabolic control. However including protein rich food into the diet and simply estimating all Phe-intake appears insufficient. The simplification of dietary regime may be helpful in enhancing acceptability and feasibility.

Glycogen storage disease type III: modified Atkins diet improves myopathy.

BACKGROUND: Frequent feeds with carbohydrate-rich meals or continuous enteral feeding has been the therapy of choice in glycogen storage disease (Glycogenosis) type III. Recent guidelines on diagnosis and management recommend frequent feedings with high complex carbohydrates or cornstarch avoiding fasting in children, while in adults a low-carb-high-protein-diet is recommended. While this regimen can prevent hypoglycaemia in children it does not improve skeletal and heart muscle function, which are compromised in patients with glycogenosis IIIa. Administration of carbohydrates may elicit reactive hyperinsulinism, resulting in suppression of lipolysis, ketogenesis, gluconeogenesis, and activation of glycogen synthesis. Thus, heart and skeletal muscle are depleted of energy substrates. Modified Atkins diet leads to increased blood levels of ketone bodies and fatty acids. We hypothesize that this health care intervention improves the energetic balance of muscles. METHODS: We treated 2 boys with glycogenosis IIIa aged 9 and 11 years with a modified Atkins diet (10 g carbohydrate per day, protein and fatty acids ad libitum) over a period of 32 and 26 months, respectively. RESULTS: In both patients, creatine kinase levels in blood dropped in response to Atkins diet. When diet was withdrawn in one of the patients he complained of chest pain, reduced physical strength and creatine kinase levels rapidly increased. This was reversed when Atkins diet was reintroduced. One patient suffered from severe cardiomyopathy which significantly improved under diet. Patients with glycogenosis IIIa benefit from an improved energetic state of heart and skeletal muscle by introduction of Atkins diet both on a biochemical and clinical level. Apart from transient hypoglycaemia no serious adverse effects were observed.

Cross-sectional study of 168 patients with hepatorenal tyrosinaemia and implications for clinical practice.

BACKGROUND: Hepatorenal tyrosinaemia (Tyr 1) is a rare inborn error of tyrosine metabolism. Without treatment, patients are at high risk of developing acute liver failure, renal dysfunction and in the long run hepatocellular carcinoma. The aim of our study was to collect cross-sectional data. METHODS: Via questionnaires we collected retrospective data of 168 patients with Tyr 1 from 21 centres (Europe, Turkey and Israel) about diagnosis, treatment, monitoring and outcome. In a subsequent consensus workshop, we discussed data and clinical implications. RESULTS: Early treatment by NTBC accompanied by diet is essential to prevent serious complications such as liver failure, hepatocellular carcinoma and renal disease. As patients may remain initially asymptomatic or develop uncharacteristic clinical symptoms in the first months of life newborn mass screening using succinylacetone (SA) as a screening parameter in dried blood is mandatory for early diagnosis. NTBC-treatment has to be combined with natural protein restriction supplemented with essential amino acids. NTBC dosage should be reduced to the minimal dose allowing metabolic control, once daily dosing may be an option in older children and adults in order to increase compliance. Metabolic control is judged by SA (below detection limit) in dried blood or urine, plasma tyrosine (<400 µM) and NTBC-levels in the therapeutic range (20-40 µM). Side effects of NTBC are mild and often transient. Indications for liver transplantation are hepatocellular carcinoma or failure to respond to NTBC. Follow-up procedures should include liver and kidney function tests, tumor markers and imaging, ophthalmological examination, blood count, psychomotor and intelligence testing as well as therapeutic monitoring (SA, tyrosine, NTBC in blood). CONCLUSION: Based on the data from 21 centres treating 168 patients we were able to characterize current practice and clinical experience in Tyr 1. This information could form the basis for clinical practice recommendations, however further prospective data are required to underpin some of the recommendations.

Treatment of arginase deficiency revisited: guanidinoacetate as a therapeutic target and biomarker for therapeutic monitoring.

Hyperargininaemia is a disorder of the last step of the urea cycle. It is an autosomal recessive disease caused by deficiency of liver arginase-1 and usually presents later in childhood with progressive neurological symptoms including marked spasticity. In contrast with other urea cycle disorders, hyperammonaemia is not usually present but can be a feature. A number of guanidine compounds may accumulate in the blood and cerebrospinal fluid of these patients, which could play an important pathophysiological role. Guanidinoacetate is of particular interest as a well-known potent epileptogenic compound in guanidinoacetate methyltransferase deficiency. We found markedly elevated guanidinoacetate levels in a patient with arginase deficiency, which dropped significantly in response to dietary and medical treatment. Measurement of guanidinoacetate and other guanidino compounds may, therefore, be important for therapeutic monitoring in arginase deficiency.

Lysine-Restricted Diet as Adjunct Therapy for Pyridoxine-Dependent Epilepsy: The PDE Consortium Consensus Recommendations.

BACKGROUND: Seventy-five percent of patients with pyridoxine-dependent epilepsy (PDE) due to Antiquitin (ATQ) deficiency suffer from developmental delay and/or intellectual disability (IQ < 70) despite seizure control. An observational study showed that adjunct treatment with a lysine-restricted diet is safe, results in partial normalization of lysine intermediates in body fluids, and may have beneficial effects on seizure control and psychomotor development. METHODS: In analogy to the NICE guideline process, the international PDE Consortium, an open platform uniting scientists and clinicians working in the field of this metabolic epilepsy, during four workshops (2010-2013) developed a recommendation for a lysine-restricted diet in PDE, with the aim of standardizing its implementation and monitoring of patients. Additionally, a proposal for a further observational study is suggested. RESULTS: (1) All patients with confirmed ATQ deficiency are eligible for adjunct treatment with lysine-restricted diet, unless treatment with pyridoxine alone has resulted in complete symptom resolution, including normal behavior and development. (2) Lysine restriction should be started as early as possible; the optimal duration remains undetermined. (3) The diet should be implemented and the patient be monitored according to these recommendations in order to assure best possible quality of care and safety. DISCUSSION: The implementation of this recommendation will provide a unique and a much needed opportunity to gather data with which to refine the recommendation as well as improve our understanding of outcomes of individuals affected by this rare disease. We therefore propose an international observational study that would utilize freely accessible, online data sharing technologies to generate more evidence.

Lysine restricted diet for pyridoxine-dependent epilepsy: first evidence and future trials.

OBJECTIVE: To evaluate the efficacy and safety of dietary lysine restriction as an adjunct to pyridoxine therapy on biochemical parameters, seizure control, and developmental/cognitive outcomes in children with pyridoxine-dependent epilepsy (PDE) caused by antiquitin (ATQ) deficiency. METHODS: In this observational study, seven children with confirmed ATQ deficiency were started on dietary lysine restriction with regular nutritional monitoring. Biochemical outcomes were evaluated using pipecolic acid and α-aminoadipic semialdehyde (AASA) levels in body fluids; developmental/cognitive outcomes were evaluated using age-appropriate tests and parental observations. RESULTS: Lysine restriction was well tolerated with good compliance; no adverse events were reported. Reduction in biomarker levels (measurement of the last value before and first value after initiation of dietary lysine restriction) ranged from 20 to 67% for plasma pipecolic acid, 13 to 72% for urinary AASA, 45% for plasma AASA and 42% for plasma P6C. For the 1 patient in whom data were available and who showed clinical deterioration upon interruption of diet, cerebrospinal fluid levels decreased by 87.2% for pipecolic acid and 81.7% for AASA. Improvement in age-appropriate skills was observed in 4 out of 5 patients showing pre-diet delays, and seizure control was maintained or improved in 6 out 7 children. CONCLUSIONS: This observational study provides Level 4 evidence that lysine restriction is well tolerated with significant decrease of potentially neurotoxic biomarkers in different body compartments, and with the potential to improve developmental outcomes in children with PDE caused by ATQ deficiency. To generate a strong level of evidence before this potentially burdensome dietary therapy becomes the mainstay treatment, we have established: an international PDE consortium to conduct future studies with an all-inclusive integrated study design; a website containing up-to-date information on PDE; a methodological toolbox; and an online registry to facilitate the participation of interested physicians, scientists, and families in PDE research.

Early cataract formation due to galactokinase deficiency: impact of newborn screening.

BACKGROUND AND AIMS: Galactokinase (GALK) deficiency is an autosomal recessive disorder causing cataract formation that can be prevented or mitigated by early diagnosis and galactose-restricted diet. The aim of this retrospective study was to explore whether GALK-deficiency meets the criteria for neonatal mass screening programs. METHODS: From 2000 until 2010, the Screening Laboratory Hannover performed newborn screening in 1,950,927 infants from Germany for galactosemia by measuring galactose-1-phosphate-uridyl-transferase and total galactose concentration (free galactose plus galactose-1-phosphate), including automatic screening for GALK deficiency. RESULTS: Eleven cases were found with elevated galactose levels accompanied by normal transferase activity. Nine of 11 cases were informative; the diagnosis was established by demonstrating deficient activity of the GALK enzyme in erythrocytes. To our knowledge, screening did not produce any false negative results. All patients were treated with a galactose-restricted diet from the neonatal period or infancy. Three of nine patients suffered from congenital cataracts or eventual development of cataracts, despite normal galactose concentrations in blood. CONCLUSIONS: Newborn screening for GALK deficiency prevents or at least mitigates cataract formation. As screening for GALK deficiency is technically simple, it seems to be reasonable to include this disorder in routine screening programs by simultaneous determination of transferase activity and quantification of galactose plus galactose-1-phosphate in dried blood spots.

Glycogen storage disease type 1: impact of medium-chain triglycerides on metabolic control and growth.

BACKGROUND/OBJECTIVE: Hypoketotic hypoglycaemia and hypertriglyceridaemia are biochemical hallmarks of glycogen storage disease (GSD) 1. Increased malonyl coenzyme A production which compromises oxidation of long-chain fatty acids via carnitine palmitoyltransferase (CPT) 1 inhibition plays a crucial role in the pathogenesis of these complications. Therapy consists primarily of nutritional support including frequent carbohydrate-rich meals. We studied the effect of a diet enriched in medium-chain triglycerides (MCT) on metabolic control/growth in GSD 1 as medium-chain fatty acids can be oxidised independently of CPT 1. METHODS: An adult female, a 1.6-year-old boy with GSD 1a and a 6.5-year-old girl with GSD 1b treated with a classical GSD diet were enrolled; their 'classical GSD diet' was supplemented with MCT fats. Concentrations of glucose, lactate, ketone bodies triglycerides, uric acid, acylcarnitines in blood and organic acids in urine were determined. RESULTS: No clinical or biochemical side-effects were observed. The MCT diet led to a decrease in uric acid concentrations in all patients. Triglyceride levels were reduced only in the youngest patient, while lactate concentrations did not significantly decrease. The MCT diet allowed for a reduction in carbohydrate and caloric intake required to maintain euglycaemia and led to improvement in growth in the two prepubertal patients. CONCLUSIONS: MCT supplementation had a positive effect on metabolic control and growth in our patients suffering from GSD 1.

The two-component system PhoPR of Clostridium acetobutylicum is involved in phosphate-dependent gene regulation.

The phoPR gene locus of Clostridium acetobutylicum ATCC 824 comprises two genes, phoP and phoR. Deduced proteins are predicted to represent a response regulator and sensor kinase of a phosphate-dependent two-component regulatory system. We analyzed the expression patterns of phoPR in P(i)-limited chemostat cultures and in response to P(i) pulses. A basic transcription level under high-phosphate conditions was shown, and a significant increase in mRNA transcript levels was found when external P(i) concentrations dropped below 0.3 mM. In two-dimensional gel electrophoresis experiments, a 2.5-fold increase in PhoP was observed under P(i)-limiting growth conditions compared to growth with an excess of P(i). At least three different transcription start points for phoP were determined by primer extension analyses. Proteins PhoP and an N-terminally truncated *PhoR were individually expressed heterologously in Escherichia coli and purified. Autophosphorylation of *PhoR and phosphorylation of PhoP were shown in vitro. Electromobility shift assays proved that there was a specific binding of PhoP to the promoter region of the phosphate-regulated pst operon of C. acetobutylicum.

Transcription of the pst operon of Clostridium acetobutylicum is dependent on phosphate concentration and pH.

The pst operon of Clostridium acetobutylicum ATCC 824 comprises five genes, pstS, pstC, pstA, pstB, and phoU, and shows a gene architecture identical to that of Escherichia coli. Deduced proteins are predicted to represent a high-affinity phosphate-specific ABC (ATP-binding cassette) transport system (Pst) and a protein homologous to PhoU, a negative phosphate regulon regulator. We analyzed the expression patterns of the pst operon in P(i)-limited chemostat cultures during acid production at pH 5.8 or solvent production at pH 4.5 and in response to P(i) pulses. Specific mRNA transcripts were found only when external P(i) concentrations had dropped below 0.2 mM. Two specific transcripts were detected, a 4.7-kb polycistronic mRNA spanning the whole operon and a quantitatively dominating 1.2-kb mRNA representing the first gene, pstS. The mRNA levels clearly differed depending on the external pH. The amounts of the full-length mRNA detected were about two times higher at pH 5.8 than at pH 4.5. The level of pstS mRNA increased by a factor of at least 8 at pH 5.8 compared to pH 4.5 results. Primer extension experiments revealed only one putative transcription start point 80 nucleotides upstream of pstS. Thus, additional regulatory sites are proposed in the promoter region, integrating two different extracellular signals, namely, depletion of inorganic phosphate and the pH of the environment. After phosphate pulses were applied to a phosphate-limited chemostat we observed faster phosphate consumption at pH 5.8 than at pH 4.5, although higher optical densities were recorded at pH 4.5.