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Airlift bioreactors (ALBs) offer advantages over conventional systems, such as simplicity of construction, reduced risk of contamination, and efficient gas-liquid dispersion with low power consumption. ALBs are usually operated under atmospheric pressure. However, in bioprocesses with high oxygen demand, such as high cell density cultures, oxygen limitation may occur even when operating with high superficial gas velocity and air enriched with oxygen. One way of overcoming this drawback is to pressurize the reactor. In this configuration, it is important to assess the influence of bioreactor internal pressure on the gas hold-up, volumetric oxygen transfer coefficient (k(L)a), and volumetric oxygen transfer rate (OTR). Experiments were carried out in a concentric-tube airlift bioreactor with a 5 dm(3) working volume, equipped with a system for automatic monitoring and control of the pressure, temperature, and inlet gas flow rate. The results showed that, in disagreement with previous published results for bubble column and external loop airlift reactors, overpressure did not significantly affect k(L)a within the studied ranges of pressure (0.1-0.4 MPa) and superficial gas velocity in the riser (0.032-0.065 m s(-1)). Nevertheless, a positive effect on OTR was observed: it increased up to 5.4 times, surpassing by 2.3 times the oxygen transfer in a 4 dm(3) stirred tank reactor operated under standard cultivation conditions. These results contribute to the development of non-conventional reactors, especially pneumatic bioreactors operated using novel strategies for oxygen control.

Background: Aromatic amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive disorder resulting in a combined dopamine and serotonin deficiency. About 50% of the cases set in the neonatal period. Here, we report an atypical clinical presentation with moderate symptoms.Patient: At 10 months old, the patient presented paroxysmal eye movements without seizures, and feeding difficulties which were attributed to gastroesophageal reflux. She was investigated at the age of 7 years, because of orofacial dyspraxia, hypomimie, axial hypotonia and focal segmental dystonia, bilateral ptosis, without evidence for cognitive impairment.Results: HVA [110 nM; (reference value (rv): 202-596)] and HIAA (12 nM; rv: 87-366) decreased, OMD (520 nM; rv: 5-60) and 5-HTP (56 nM; rv: 2-16) increased in CSF. We confirmed the diagnosis of AADC deficiency because the activity in plasma was low: 4 pmol/min/ml; rv: 16-137. The kinetic analysis revealed a sixfold increase in the apparent affinity for L-dopa (4.26 mM; control ¼ 0.71), but the V max was unchanged (37.5 pmol dopamine/min/ml; control ¼ 39.1), suggesting a modification in the substrate binding-site. Molecular analysis revealed two heterozygous mutations in the DDC gene: c1040G > A; pR347Q already described, and a novel mutation c478C > T, pR160W.Conclusion: (1) CSF neurotransmitters metabolites suggested a moderate AADC deficiency; (2) The initial velocity saturation curve for L-dopa displayed a cooperative ligand binding behavior, in keeping with the modifications of the three-dimensional structure, induced by the amino acid substitutions (3) The treatment combination of L-dopa with pyridoxine dramatically improved the quality of life, the fatigability, and the paroxysmal eye movements. Abbreviations 3DThree dimensional 3-OMD 3-Ortho-methyldopa 5-HIAA 5-Hydroxyindolacetic acid 5-HT 5-Hydroxytryptamine 5-HTP 5-Hydroxytryptophan AADC Aromatic L-amino acid decarboxylase CSF Cerebral spinal fluid DA Dopamine JIMD Reports

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