Intracellular glycerol accumulation in light-limited Dunaliella tertiolecta culture is determined by partitioning of glycerol across the cell membrane.

Dunaliella accumulates intracellular glycerol to counterbalance the extracellular salinity. In N-limited chemostat cultures of D. tertiolecta, total glycerol production (sum of intracellular and extracellular) and intracellular glycerol content were proportional to the salinity of the culture medium. In the light-limited D. tertiolecta culture, total glycerol output (sum of intracellular and extracellular) was relatively constant at different salinities (0.5 and 2.0 M), while the intracellular glycerol content was proportional to the culture medium salinity, that is, the cells released less glycerol into the culture medium, rather than de novo synthesis of glycerol at high culture medium salinity. The study implies different regulatory mechanisms in the accumulation of intracellular glycerol in N-limited and light-limited D. tertiolecta in response to salinity.

Continual production of glycerol from carbon dioxide by Dunaliella tertiolecta.

Microalgae have high photosynthetic efficiencies and produce many valuable compounds from carbon dioxide. The Dunaliella genus accumulates glycerol, yet no commercial process currently exists for glycerol production from this microalga. Here it was found that in addition to intracellular accumulation, Dunaliella tertiolecta also releases glycerol into the external medium continuously, forming a large and stable carbon pool. The process is not affected by nutrient starvation or onset of cell death. Carbon dioxide was fixed at a constant rate, the bulk of it being channelled to extracellular glycerol (82%), resulting in enhanced photosynthetic carbon assimilation of 5 times that used for biomass production. The final extracellular glycerol concentration was 34 times the maximum concentration of intracellular glycerol; the latter declined further during cell death. Findings from this work will assist in the development of a bioconversion process to produce glycerol using D. tertiolecta without the need for cell harvest or disruption.

Amniotic fluid lamellar body concentration as a marker of fetal lung maturity at term elective caesarean delivery.

BACKGROUND: Caesarean birth, without prior labour, is associated with an increased risk of neonatal respiratory morbidity among term infants. The concentration of lamellar bodies in amniotic fluid reflects pulmonary surfactant production and release, and is thus used in preterm populations as a marker of fetal lung maturity. Whether amniotic fluid lamellar body concentration (AFLBC) may correlate with risk factors for term respiratory distress has not previously been evaluated. AIMS: To determine the relationship between AFLBC and risk factors for respiratory distress following term caesarean birth. METHODS: The AFLBC of 249 women at the time of term caesarean birth was examined for an association with gestational age, gender, presentation and neonatal respiratory distress requiring special care nursery (SCN) admission. RESULTS: There was a significant increase in AFLBC with gestation. When compared with caesarean deliveries performed during the 37th week of gestation, there was a 50%, 54% and 56% increase in lamellar body concentrations (LBCs) taken during the 38th, 39th and 40th week of gestation respectively (P < 0.05 for all). Female fetuses had a 16% higher LBC than males (P < 0.05). An LBC <100 x 10(9) mL(-1) was associated with increased risk of admission to the SCN with respiratory distress (RR = 5.6; 1.2-26.5, P < 0.05). CONCLUSION: Known risk factors for term respiratory distress are reflected in the AFLBC. A significant relationship exists between AFLBC and respiratory morbidity following term caesarean birth. However, the low prevalence of this condition limits the clinical role of AFLBC as a predictive test for term respiratory morbidity.

Word recognition and cognitive profiles of Chinese pre-school children at risk for dyslexia through language delay or familial history of dyslexia.

BACKGROUND: This study sought to identify cognitive abilities that might distinguish Hong Kong Chinese kindergarten children at risk for dyslexia through either language delay or familial history of dyslexia from children who were not at risk and to examine how these abilities were associated with Chinese word recognition. The cognitive skills of interest were syllable awareness, tone detection, rapid automated naming, visual skill, and morphological awareness. METHOD: We recruited 36 children whose sibling had been previously diagnosed with dyslexia (familial risk group) and 36 children who were initially reported to have difficulties in preschool literacy acquisition by either teachers or parents and subsequently found to demonstrate clinical at-risk factors in aspects of language by paediatricians (language delayed group); the mean age of these groups was approximately 61 months. Thirty-six children with no such risk factors were matched by age, IQ, and parents' education to the at-risk groups. All children were tested on cognitive skills and Chinese word recognition. RESULTS: Compared to the controls, children in the language delayed group scored significantly lower on all measures, whereas children in the familial risk group performed significantly worse only on tone detection, morphological awareness, and Chinese word recognition. In regression analyses, word recognition was best explained by morphological awareness, tone detection and visual skill. CONCLUSIONS: Language-related measures are strongly associated with early reading development and impairment in Hong Kong Chinese children. Tests of tone detection and morphological awareness may be important clinical tools for diagnosing risk for reading problems in young Chinese children. In contrast, Chinese language delay may be associated with broader cognitive impairments as found previously in various Indo-European languages (e.g., Bishop & Snowling, 2004).

Kinetic analysis and modelling of enzymatic (R)-phenylacetylcarbinol batch biotransformation process.

Initial rate and biotransformation studies were applied to refine and validate a mathematical model for enzymatic (R)-phenylacetylcarbinol (PAC) production from pyruvate and benzaldehyde using Candida utilis pyruvate decarboxylase (PDC). The rate of PAC formation was directly proportional to the enzyme activity level up to 5.0 U ml-1 carboligase. Michaelis-Menten kinetics were determined for the effect of pyruvate concentration on the reaction rate. The effect of benzaldehyde followed the sigmoidal shape of the Monod-Wyman-Changeux (MWC) model. The biotransformation model, which also included a term for PDC inactivation by benzaldehyde, was used to determine the overall rate constants for the formation of PAC, acetaldehyde, and acetoin. These values were determined from data for three batch biotransformations performed over a range of initial concentrations (viz. 50-150 mM benzaldehyde, 60-180 mM pyruvate, 1.1-3.4 U ml-1 enzyme activity). The finalized model was then used to predict a batch biotransformation profile at 120/100 mM initial pyruvate/benzaldehyde (initial enzyme activity 3.0 U ml-1). The simulated kinetics gave acceptable fitting (R2 = 0.9963) to the time courses of these latter experimental data for substrates pyruvate and benzaldehyde, product PAC, by-products acetaldehyde and acetoin, as well as enzyme activity level.