Biosynthesis of spheroidene and hydroxyspheroidene in Rhodopseudomonas species: experiments with nicotine as inhibitor (Short Communication)

Neurosporene replaces spheroidene and hydroxyspheroidene as the main carotenoid in Rhodopseudomonas spheroides and Rhodopseudomonas gelatinosa grown in the presence of nicotine. On removal of the nicotine, spheroidene and hydroxyspheroidene are formed at the expense of the accumulated neurosporene. This shows that nicotine inhibits introduction of the C-1 tertiary hydroxyl groups, and supports the postulated pathway neurosporene-->spheroidene-->hydroxyspheroidene.     

Use of deuterium labelling from deuterium oxide to demonstrate carotenoid transformations in photosynthetic bacteria

Carotenoid biosynthesis in many purple photosynthetic bacteria of the Rhodospirillaceae is inhibited by nicotine, and biosynthetic intermediates accumulate. If the inhibitor is removed and the bacteria are then incubated in buffered 99.6% deuterium oxide, deuterium is incorporated specifically into the C-2 position in both cyclic and acyclic carotenoids that are then formed from the previously accumulated hydrocarbon precursors. The deuterated molecular species can be detected and assayed by mass spectrometry. By use of this procedure, direct proof has been obtained for the conversion of lycopene into β-carotene and rhodopin in Rhodomicrobium vannielii, of neurosporene into spheroidene in Rhodopseudomonas sphaeroides and of spheroidene into hydroxyspheroidene in Rps. gelatinosa. The results confirm the operation of the biosynthetic pathways postulated for these organisms, and prove that formation of the acyclic 1-hydroxy-1,2-dihydro end-group characteristic of the carotenoids of photosynthetic bacteria occurs by addition of water to the C-1,2 double band.     

Epidemic modelling: Aspects where stochasticity matters

Epidemic models are always simplifications of real world epidemics. Which real world features to include, and which simplifications to make, depend both on the disease of interest and on the purpose of the modelling. In the present paper we discuss some such purposes for which a stochastic model is preferable to a deterministic counterpart. The two main examples illustrate the importance of allowing the infectious and latent periods to be random when focus lies on the probability of a large epidemic outbreak and/or on the initial speed, or growth rate, of the epidemic. A consequence of the latter is that estimation of the basic reproduction number R₀ is sensitive to assumptions about the distributions of the infectious and latent periods when using data from the early stages of an outbreak, which we illustrate with data from the H1N1 influenza A pandemic. Some further examples are also discussed as are some practical consequences related to these stochastic aspects.     

Investigation into the increase in hay fever and eczema at age 16 observed between the 1958 and 1970 British birth cohorts.

OBJECTIVE: To investigate whether changes in certain perinatal and social factors explain the increased prevalence of hay fever and eczema among British adolescents between 1974 and 1986. DESIGN: Two prospective birth cohort studies. SETTING: England, Wales, and Scotland. SUBJECTS: 11,195 children born 3-9 March 1958 and 9387 born 5-11 April 1970. MAIN OUTCOME MEASURES: Parental reports of eczematous rashes and of hay fever or allergic rhinitis in the previous 12 months at age 16. RESULTS: The prevalence of the conditions over the 12 month period increased between 1974 and 1986 from 3.1% to 6.4% (prevalence ratio 2.04 (95% confidence interval 1.79 to 2.32)) for eczema and from 12.0% to 23.3% (prevalence ratio 1.93 (1.82 to 2.06)) for hay fever. Both conditions were more commonly reported among children of higher birth order and those who were breast fed for longer than 1 month. Eczema was more commonly reported among girls and hay fever among boys. The prevalence of hay fever decreased sharply between social classes I and V, increased with maternal age up to the early 30s, and was lower in children whose mothers smoked during pregnancy. Neither condition varied significantly with birth weight. When adjusted for these factors, the relative odds of hay fever (1986 v 1974) increased from 2.23 (2.05 to 2.43) to 2.40 (2.19 to 2.63). Similarly, the relative odds of eczema rose from 2.02 (1.73 to 2.36) to 2.14 (1.81 to 2.52). CONCLUSIONS: Taken together, changes between cohorts in sex, birth weight, birth order, maternal age, breast feeding, maternal smoking during pregnancy, and father''s social class at birth did not seem to explain any of the observed rise in the prevalence of hay fever and eczema. However, correlates of these factors which have changed over time may still underlie recent increases in allergic disease.     

Biofeedback treatment of atopic dermatitis: controlled case studies of eight cases.

To investigate the feasibility of a behaviorally oriented intervention program with atopic dermatitis, 12 patients were exposed to a fixed sequence of treatment phases including a no-treatment baseline phase, a phase incorporating nonspecific treatment factors, and a phase involving frontal electromyographic (EMG) feedback and relaxation instructions. Photographic analyses of involved skin areas revealed significant remission of dermatological problems across the entire program, although significant changes could not be attributable to any specific phase. Ratings of itching level decreased within but not across treatment sessions, and variable correlations across subjects were found between frontal EMG and itching level. MMPI results from the dermatitis subjects were within normal limits. Overall, the results provided mixed support for the hypothesis that atopic dermatitis may be amenable to intervention through behaviorally oriented treatment procedures.