An electrogenetic toggle switch model

Synthetic biology uses molecular biology to implement genetic circuits that perform computations. These circuits can process inputs and deliver outputs according to predefined rules that are encoded, often entirely, into genetic parts. However, the field has recently begun to focus on using mechanisms beyond the realm of genetic parts for engineering biological circuits. We analyse the use of electrogenic processes for circuit design and present a model for a merged genetic and electrogenetic toggle switch operating in a biofilm attached to an electrode. Computational simulations explore conditions under which bistability emerges in order to identify the circuit design principles for best switch performance. The results provide a basis for the rational design and implementation of hybrid devices that can be measured and controlled both genetically and electronically.     

Production of pectinases by Aspergillus niger in solid state fermentation at high initial glucose concentrations

Exopectinase (exo-p) and endopectinase (endo-p) production by Aspergillus niger CH4 in solid state culture was studied at initial glucose concentrations of 100, 250, 350 and 450 g/l. The highest activity of exo-p (35 U/g) was produced at 72 and 120 h in the medium containing 100 and 250 g glucose/l, respectively. The maximum endo-p activity (9 U/g) was produced at 72 h in the medium with 250 g glucose/l. The reduction in pectinase production at 350 and 450 g/l initial glucose concentration was due neither to repression of the synthesis of the enzyme nor to the glucose consumption rate of the strain but due to a drastic drop in pH of the medium.S. Solis-Pereyra, E. Favela-Torres, M. Gutiérrez-Rojas, G. Saucedo-Castañeda and G. Viniegra-González are with the Departamento de Biotecnologia, Universidad Autónoma Metropolitana, A.P. 55-535, C.P. 09340, México D.F., México; S. Roussos is with the Laboratoire de Biotechnologie, ORSTOM, B.P. 5045, 34032, Montpellier Cedex, France, and P. Gunasekaran is with the Department of Microbial Technology, School of Biological Sciences, Madurai Kamaraj University, Madurai, 625-021, India.     

Manipulating photosynthesis

The levels of individual photosynthetic proteins can be independently decreased by theAgrobacterium-mediated transformation of plants with antisens RNA constructs. Protocols for the introduction of such constructs intoAgrobacterium, theAgrobacterium-mediated transformation of tobacco leaf disks, and the screening and analysis of the transgenic plants produced are described.     

The peptide antibiotic microcin 25 is imported through the TonB pathway and the SbmA protein.

Selection of spontaneous mutants for insensitivity to the peptide antibiotic microcin 25 led to the isolation of five categories of mutants. Phenotypic and mapping studies showed the mutations to be located in the fhuA, exb, tonB, and sbmA genes. The latter encodes a cytoplasmic membrane protein which is also required for the penetration of microcin B17.     

Automatic gas meter for laboratory fermenters

Summary A versatile, cheap and automated system is designed for the measurement of small gas flows produced in laboratory-scale fermentation processes. An automatic sampling device for programmed times is linked to the flow meter. The displacement of a liquid by the gas being measured is the principle on which both the meter and the sampling device are based. The operation of the system is controlled by a simple electronic circuit.     

Changes in blood level of catecholamines during arterial blood pressure rise induced with sciatic nerve stimulation

In experiments on rabbits and dogs it was demonstrated that electrical stimulation of the centripetal fibres of the cut sciatic nerve causing a rise of the arterial blood pressure produced a significant increase in the plasma levels of adrenaline and noradrenaline. This effect was not observed in animals with sympathetic system blockade caused by administration of reserpine. These observations indicate that pressure increase after sciatic nerve stimulation is due to stimulation of the adrenergic system.     

Batch culture of Candida utilis in a medium deprived of a phosphorous source

Summary Candida utilis var. major NRRL-Y-1084 was grown in a defined medium without a phosphorous (P) source. During the exponential phase, cells divided according to a specific growth rate of 0.32 h^-1, which is lower than the usual rate for a balanced medium (0.4–0.6 h^-1). The relative P content of the biomass decreased from 2.70% to 0.75% over a period of 6 h, including 2 h of cell division arrest. At the end of this period there was another interruption of cell division. After that, multiplication restarted at a considerably lower rate and it deviated slightly from the exponential pattern. The stationary phase began when biomass P content reached 0.4%–0.5%, slowly decreasing afterwards to 0.25–0.20%. Biomass synthesis was less affected than cell division by the relative decrease of endogenous P, the two processes differing partially in their kinetics. Cell lysis started shortly before the stationary phase and affected about 20% of the population by the end of the assay. RNA and P content of the resulting biomass were 2.4% and 0.25% respecitvely, P being mainly incorporated to RNA.The relationship of biomass production to glucose uptake was very low, probably because the marked P deficiency called for an increase in energy consumption for growth and specially for maintenance. Compared with yeasts grown in a balanced medium, 40% increase in glycogen was observed, whereas no mean changes in the content of cell wall carbohydrates (glucan and mannan) and that of true protein were found.Member of the Scientific Researcher's Career of the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET). Agrentina     

Biosynthetic approach to the structure of F1-ATPase (BF1 factor) from Micrococcus lysodeikticus membranes: in vivo labeling of the polypeptides and study of their relationship

The F₁-ATPase or BF₁ factor was purified from Micrococcus lysodeikticus substrain B grown in a synthetic medium in the presence of tritiated amino acids. When analyzed in sodium dodecyl sulfate-7% polyacrylamide gels, the fresh purified preparation contained α, β, γ subunits (referred as the intrinsic subunits) and two other polypeptides (designated as X and component of relative mobility 1.0) whose status as subunits remains to be established. This overall polypeptide composition was similar to that of the F₁-ATPase isolated from the same strain grown in complex medium (J. Carreira, J. M. Andreu, M. Nieto, and E. Muñoz., 1976 Mol. Cell. Biochem.10, 67–76). The distribution of ³H-labeled amino acids into purified F₁-ATPase and its constituent polypeptides under different stages of growth was used to investigate the biosynthetic relationship between the different polypeptides. The incorporation of amino acids into purified BF₁ factor was slower than that of cytoplasmic and other membrane proteins. In isotope-dilution and chase experiments, F₁-ATPase showed one of the slowest rates of decay of the incorporated label. These results point out that F₁-ATPase of M. lysodeikticus undergoes slower turnover than the overall cytoplasmic and membrane proteins. Pulse and chase experiments allowed us to conclude that the α, β, γ subunits and the components of relative mobility 1.0 are independent with differences in their turnover and therefore do not bear any apparent relation as precursors-products. The two major subunits represent seemingly the “core” of ATPase, the β subunit behaving like the most stable component. On the other hand, the γ subunit appears to be synthesized independently from this α + β complex.     

Occurrence of subcutaneous zygomycosis (Entomophthoromycosis Basidiobolae) caused by Basidiobolus haptosporus with pulmonary involvement

A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest.     

Retinoblastoma,gross internal malformations,and deletion 13q14→q31

Summary A male patient with an interstitial deletion 13q14q31 is described. Our necropsy findings included a left retinoblastoma and several gross internal malformations. In this paper we reaffirm that band 13q14 is involved in cases of retinoblastoma and we propose, after studying accompanying cases of total or partial long arm trisomies 13, that the loss of specific 13q bands, from 13q14 to 13q31 is responsible for the congenital defects we are describing.