The influence of initial xylose concentration, agitation, and aeration on ethanol production by Pichia stipitis from rice straw hemicellulosic hydrolysate

Rice straw hemicellulosic hydrolysate was used as fermentation medium for ethanol production by Pichia stipitis NRRL Y-7124. Shaking bath experiments were initially performed aiming to establish the best initial xylose concentration to be used in this bioconversion process. In the sequence, assays were carried out under different agitation (100 to 200 rpm) and aeration (V flask/V medium ratio varying from 2.5 to 5.0) conditions, and the influence of these variables on the fermentative parameters values (ethanol yield factor, Y P/S; cell yield factor, Y X/S; and ethanol volumetric productivity, Q P) was investigated through a 22 full-factorial design. Initial xylose concentration of about 50 g/l was the most suitable for the development of this process, since the yeast was able to convert substrate in product with high efficiency. The factorial design assays showed a strong influence of both process variables in all the evaluated responses. The agitation and aeration increase caused a deviation in the yeast metabolism from ethanol to biomass production. The best results (Y P/S = 0.37 g/g and Q P = 0.39 g/l.h) were found when the lowest aeration (2.5 V flask/V medium ratio) and highest agitation (200 rpm) levels were employed. Under this condition, a process efficiency of 72.5% was achieved. These results demonstrated that the establishment of adequate conditions of aeration is of great relevance to improve the ethanol production from xylose by Pichia stipitis, using rice straw hemicellulosic hydrolysate as fermentation medium.The financial support from Fapesp (Brazil) is gratefully acknowledged

Random UV-C mutagenesis of Scheffersomyces (formerly Pichia) stipitis NRRL Y-7124 to improve anaerobic growth on lignocellulosic sugars

Scheffersomyces (formerly Pichia) stipitis NRRL Y-7124 was mutagenized using UV-C irradiation to produce yeast strains for anaerobic conversion of lignocellulosic sugars to ethanol. UV-C irradiation potentially produces large numbers of random mutations broadly and uniformly over the whole genome to generate unique strains. Wild-type cultures of S. stipitis NRRL Y-7124 were subjected to UV-C (234 nm) irradiation targeted at approximately 40% cell survival. When surviving cells were selected in sufficient numbers via automated plating strategies and cultured anaerobically on xylose medium for 5 months at 28°C, five novel mutagenized S. stipitis strains were obtained. Variable number tandem repeat analysis revealed that mutations had occurred in the genome, which may have produced genes that allowed the anaerobic utilization of xylose. The mutagenized strains were capable of growing anaerobically on xylose/glucose substrate with higher ethanol production during 250- to 500-h growth than a Saccharomyces cerevisiae yeast strain that is the standard for industrial fuel ethanol production. The S. stipitis strains resulting from this intense multigene mutagenesis strategy have potential application in industrial fuel ethanol production from lignocellulosic hydrolysates

Home on the Range: Factors Explaining Partial Migration of African Buffalo in a Tropical Environment

Partial migration (when only some individuals in a population undertake seasonal migrations) is common in many species and geographical contexts. Despite the development of modern statistical methods for analyzing partial migration, there have been no studies on what influences partial migration in tropical environments. We present research on factors affecting partial migration in African buffalo (Syncerus caffer) in northeastern Namibia. Our dataset is derived from 32 satellite tracking collars, spans 4 years and contains over 35,000 locations. We used remotely sensed data to quantify various factors that buffalo experience in the dry season when making decisions on whether and how far to migrate, including potential man-made and natural barriers, as well as spatial and temporal heterogeneity in environmental conditions. Using an information-theoretic, non-linear regression approach, our analyses showed that buffalo in this area can be divided into 4 migratory classes: migrants, non-migrants, dispersers, and a new class that we call “expanders”. Multimodel inference from least-squares regressions of wet season movements showed that environmental conditions (rainfall, fires, woodland cover, vegetation biomass), distance to the nearest barrier (river, fence, cultivated area) and social factors (age, size of herd at capture) were all important in explaining variation in migratory behaviour. The relative contributions of these variables to partial migration have not previously been assessed for ungulates in the tropics. Understanding the factors driving migratory decisions of wildlife will lead to better-informed conservation and land-use decisions in this area

The logic of kinetic regulation in the thioredoxin system

<p>Abstract</p> <p>Background</p> <p>The thioredoxin system consisting of NADP(H), thioredoxin reductase and thioredoxin provides reducing equivalents to a large and diverse array of cellular processes. Despite a great deal of information on the kinetics of individual thioredoxin-dependent reactions, the kinetic regulation of this system as an integrated whole is not known. We address this by using kinetic modeling to identify and describe kinetic behavioral motifs found within the system.</p> <p>Results</p> <p>Analysis of a realistic computational model of the <it>Escherichia coli </it>thioredoxin system revealed several modes of kinetic regulation in the system. In keeping with published findings, the model showed that thioredoxin-dependent reactions were adaptable (i.e. changes to the thioredoxin system affected the kinetic profiles of these reactions). Further and in contrast to other systems-level descriptions, analysis of the model showed that apparently unrelated thioredoxin oxidation reactions can affect each other via their combined effects on the thioredoxin redox cycle. However, the scale of these effects depended on the kinetics of the individual thioredoxin oxidation reactions with some reactions more sensitive to changes in the thioredoxin cycle and others, such as the Tpx-dependent reduction of hydrogen peroxide, less sensitive to these changes. The coupling of the thioredoxin and Tpx redox cycles also allowed for ultrasensitive changes in the thioredoxin concentration in response to changes in the thioredoxin reductase concentration. We were able to describe the kinetic mechanisms underlying these behaviors precisely with analytical solutions and core models.</p> <p>Conclusions</p> <p>Using kinetic modeling we have revealed the logic that underlies the functional organization and kinetic behavior of the thioredoxin system. The thioredoxin redox cycle and associated reactions allows for a system that is adaptable, interconnected and able to display differential sensitivities to changes in this redox cycle. This work provides a theoretical, systems-biological basis for an experimental analysis of the thioredoxin system and its associated reactions.</p

Lions, trophy hunting and beyond, known unknowns and why they matter

What does trophy hunting contribute to wild lion conservation? What constitutes best practice? D.W. Macdonald (2016) summarises what we know. However, in the much, but perhaps unfairly, mocked words of Donald Rumsfeld, there are knowns, known unknowns and unknown unknowns. We identified gaps in knowledge inhibiting conservation planning in several areas: these areas included the causes of lion mortality, the amount of land used for lion trophy hunting, the extent to which trophy hunting depends on lions for financial viability, and the vulnerability of areas currently used for trophy hunting to conversion to non wildlife-based land uses if it were to cease

The effects of sports vision exercises on the visual skills of university students

Vision is one of the most important special senses and is the primary source of external information. The role of vision in our everyday lifestyles is immense and adequate visual skills are needed for simple tasks which include reading and writing, that are especially important for students. Stress is an important factor which most students deal with, and along with other external factors, could adversely affect the ability to effectively perform many visual skills. This study aims to determine if sports vision exercises could improve visual skills and thereby enhance motor and cognitive performance. A 169 second year physiology students (18-22 years of age) participated in the study. The students were divided into control (n=78) and experimental groups (n=91) and pre and post sports vision tests were conducted. This included testing visual skills such as visual acuity, eye dominance, focusing, tracking, vergence, sequencing, eye-hand coordination, visualization and reflex. The results showed a significant improvement in the sequencing and eye-hand coordination tests in the experimental group, whilst a non-significant improvement (control group) was observed in the visual acuity, visualization, tracking, vergence and reflex tests. The improvements (except for focusing) were greater in the experimental group than in the control group. The study clearly showed that correct sports vision training can improve certain visual skills and lead to an enhancement of motor and cognitive learning and performance. Sports vision exercises are therefore an efficient method of improving certain visual skills and possibly minimizing any defects caused by stress.Key words: Sports vision exercises, visual skills, students

Sex differences in the nine-point Beighton hypermobility test scores

Joint hypermobility syndromes are often misinterpreted and wrongly diagnosed. Widely accepted naming such as Heritable Disorder of Connective Tissue has been shown to manifest features that closely overlap with better known disorders such as Marfan and Ehlers-Danlos syndromes and Osteogenesis Imperfecta. Currently the widely accepted ―all-inclusive‖ diagnosis for generalised hypermobility is known as Benign Joint Hypermobility Syndrome (BJHS). People that do not have pain in their joints but still have lax joints are just considered to be hypermobile. It is currently understood that these are genetic-based conditions where connective tissue proteins such as collagen are formed differently. This results in the joints, muscles, tendons and ligaments being laxer and more fragile than is the case in non-hypermobile individuals. The aim of this study was to investigate possible differences in the occurrence of BJHS between males and females from a representative sample of a general population (aged 18-25). Testing was done on 300 recruits and 180 university students. The sample consisted of 55% males and 45% females. All subjects were tested using the 9 - point Beighton criteria for diagnosis of BJHS, with scores of 4/9 and greater being indicative of BJHS. All data were pooled and differences were observed when comparing male and female Beighton test scores. Results showed 36.41% incidence for females compared to 13.96% for males (p &le; 0.05). These differences maybe due to hormonal influence on the laxity of tendons and ligaments.&nbsp; Furthermore it can also question the efficiency with which the Beighton score distinguishes between BJHS and general joint flexibility.Keywords: Hypermobility, sex differences, Benign Joint Hypermobility Syndrome