Monitoring the convection coefficient in fermentative processes using numerical methods

Bioprocess and Biosystems Engineering - This work is based on the importance of monitoring the thermodynamic variables of sugarcane juice fermentation by Saccharomyces cerevisiae, using a numerical...     

Characterisation of Trypanosoma cruzi populations by dna polymorphism of the cruzipain gene detected by single-stranded dna conformation polymorphism (SSCP) and direct sequencing

Fifty fresh isolates of Trypanosoma cruzi from Triatoma dimidiata vectors and 31 from patients with Chagas disease were analysed for DNA polymorphisms within the 432-bp core region of the cruzipain gene which encodes the active site of cathepsin L-like cystein proteinase. The cruzipain gene showed signs of polymorphism consisting of four different DNA sequences in Central and South American isolates of T. cruzi. The PCR fragments of Guatemalan isolates could be divided into three groups, Groups 1, 2 and 3, based on different patterns of single-stranded DNA conformation polymorphism. All of the strains isolated from Brazil, Chile, and Paraguay, except for the CL strain, showed a Group 4 pattern. Two to four isolates from each group were analysed by cloning and sequencing. A silent mutation occurred between Groups 1 and 2, and five nucleotides and two aa substitutions were detected between Groups 1 and 3. The DNA sequence of Group 4 contained five nucleotides and one aa substitution from Group 1. All of the DNA sequences corresponded well with the single-stranded DNA conformation polymorphism. The Group 1 isolates, the majority in the Guatemalan population (70/81, 86.4%), were isolated from both triatomines and humans, but Group 3 were isolated only from humans. Moreover, the Group 2 isolates were detected only in triatomine vectors (9/50; 18%), but never in humans (0/32, P<0.05) suggesting that this group has an independent life-cycle in sylvatic animals and is maintained by reservoir hosts other than humans.     

Dipeptidyl aminopeptidase yspI mutants of Schizosaccharomyces pombe: Genetic mapping of dpa1+ on chromosome III

Abstract A mutant strain of Schizosaccharomyces pombe lacking dipeptidyl aminopeptidase yspI was isolated from a strain already defective in aminopeptidase activity by means of a staining technique with the chromogenic substrate ala-pro-4-methoxy-β-naphthylamide to screen colonies for the absence of the enzyme. The defect segregated 2⁺ :2⁻ in meiotic tetrads, indicating a single chromosomal gene mutation, which was shown to be recessive. Gene dosage experiments indicated that the mutation resides in the structural gene of dipeptidyl aminopeptidase yspI, dpa 1⁺. The dpa 1⁺ gene was located on chromosome III by using l m- fluorophen-ylalanine-induced haploidization and mitotic analysis. dpa1 mutants did not show any obvious phenotype under a variety of conditions tested.     

Use of manure concentrations of ash or specific minerals and nitrogen to estimate loss of volatile nitrogen from manure incubated under laboratory conditions

Changes in the ratio of volatile N to non-volatile specific minerals or total ash in manure can potentially be used to estimate losses of N from manure. The aim of this study was to evaluate the accuracy of using specific minerals (P, K, Ca, Mg, and Na) or total ash as markers to estimate volatile N losses from incubated manure slurries. Holstein cows were fed diets with the forage as predominantly corn silage (CS) or alfalfa silage (AS) or a diet identical to the CS diet except 5 g/kg urea was added (CSU). Total output of urine and feces were measured and used to prepare two types of slurry mixtures (all slurry mixtures contained 1200 g of manure per tray): (1) as excreted (AsEx) and (2) AsEx + sand (SAND). The SAND slurry was designed to mimic manure from barns that used sand as a bedding material. Feces and urine were mixed in the same proportion as excreted by the cows for both slurry types and 240 g of sand were added to the SAND slurries. Initial and final (3 d incubation period) slurry weights and concentrations of N, ash, and specific minerals were measured to calculate loss of volatile N. Losses of volatile N from the slurries were estimated as: (N intake ? N milk) ? [N/ash × (ash intake ? ash milk)], where N and ash intake = g/d consumed by the cow; N and ash milk = g/d secreted in milk; and N/ash = ratio of N and ash concentrations in slurry samples at 3 d. To evaluate specific minerals as markers, the same equation was used except that Ca, K, Mg, Na or P replaced the ash term. Measured N losses from the AsEx slurries were 0.44, 0.62, and 1.03 g/3 d for the AS, CS, and CSU treatments and estimated N losses (using N/ash) were 0.29, 0.49, and 1.14 g/3 d. Estimated losses were less than measured losses for cows with negative N balance and greater than measured losses for cows in positive N balance. For AsEx slurries, the use of N to specific mineral ratios was generally less accurate than using the N/ash ratio. Estimated N losses from SAND slurries were extremely inaccurate for all markers. The use of the N/ash ratio to estimate N volatilization from manure shows promise but markers that are in appreciable concentrations in bedding material will not be accurate.     

Positive and Negative Feedbacks and Free-Scale Pattern Distribution in Rural-Population Dynamics

Depopulation of rural areas is a widespread phenomenon that has occurred in most industrialized countries, and has contributed significantly to a reduction in the productivity of agro-ecological resources. In this study, we identified the main trends in the dynamics of rural populations in the Central Pyrenees in the 20^th C and early 21^st C, and used density independent and density dependent models and identified the main factors that have influenced the dynamics. In addition, we investigated the change in the power law distribution of population size in those periods. Populations exhibited density-dependent positive feedback between 1960 and 2010, and a long-term positive correlation between agricultural activity and population size, which has resulted in a free-scale population distribution that has been disrupted by the collapse of the traditional agricultural society and by emigration to the industrialized cities. We concluded that complex socio-ecological systems that have strong feedback mechanisms can contribute to disruptive population collapses, which can be identified by changes in the pattern of population distribution.     

A Dynamic Gene Regulatory Network Model That Recovers the Cyclic Behavior of Arabidopsis thaliana Cell Cycle

Cell cycle control is fundamental in eukaryotic development. Several modeling efforts have been used to integrate the complex network of interacting molecular components involved in cell cycle dynamics. In this paper, we aimed at recovering the regulatory logic upstream of previously known components of cell cycle control, with the aim of understanding the mechanisms underlying the emergence of the cyclic behavior of such components. We focus on Arabidopsis thaliana, but given that many components of cell cycle regulation are conserved among eukaryotes, when experimental data for this system was not available, we considered experimental results from yeast and animal systems. We are proposing a Boolean gene regulatory network (GRN) that converges into only one robust limit cycle attractor that closely resembles the cyclic behavior of the key cell-cycle molecular components and other regulators considered here. We validate the model by comparing our in silico configurations with data from loss- and gain-of-function mutants, where the endocyclic behavior also was recovered. Additionally, we approximate a continuous model and recovered the temporal periodic expression profiles of the cell-cycle molecular components involved, thus suggesting that the single limit cycle attractor recovered with the Boolean model is not an artifact of its discrete and synchronous nature, but rather an emergent consequence of the inherent characteristics of the regulatory logic proposed here. This dynamical model, hence provides a novel theoretical framework to address cell cycle regulation in plants, and it can also be used to propose novel predictions regarding cell cycle regulation in other eukaryotes.