Regulation of the lysine biosynthetic pathway in Escherichia coli K-12: isolation of a cis-dominant constitutive mutant for AK III synthesis.

A method for isolating regulatory mutants for the synthesis of lysine biosynthetic enzymes in Escherichia coli is described. One of them is identified as a cis-dominant constitutive mutant for the synthesis of the lysine-sensitive asportokinase AK III (lysC gene).     

Buoyancy of sub-Antarctic notothenioids including the sister lineage of all other notothenioids (Bovichtidae)

The radiation of notothenioid fishes (Perciformes) in Antarctic waters was likely the result of an absence of competition in the isolated Antarctic waters and key traits such as the production of antifreeze glycoprotein and buoyancy modifications. Although notothenioids lack a swim bladder, the buoyancy of Antarctic species, ranging from neutrally buoyant to relatively heavy, corresponds to diverse life styles. The buoyancy of South American notothenioids has not been studied. Static buoyancy was measured in adult notothenioids (n = 263, from six species of the sub-order Notothenioidei, families Bovichtidae, Eleginopidae, Nototheniidae, and Harpagiferidae) from the Beagle Channel. Measurements were expressed as percentage buoyancy (%B). Buoyancy ranged from 3.88 to 6.96% (median, 4.0–6.7%), and therefore, all species could be considered benthic consistent with previous studies that found that neutral buoyancy in notothenioids is rare. Harpagifer bispinis, Patagonotothen cornucola, and Cottoperca gobio were significantly less buoyant than Paranotothenia magellanica. The buoyancy values of most species were concordant with known habitat preferences. These data, especially the data of C. gobio (sister lineage of all other nototehnioids) and E. maclovinus (sister lineage of the Antarctic clade of notothenioids), could be useful for understanding the diversification of this feature during the notothenioid radiation.     

Über einige Vertreter der Eryopoidea (Amphibia: Temnospondyli) aus dem europäischen Rotliegend (? höchstes Karbon — Perm) 1.Sclerocephalus

The chronospeciesSclerocephalus bavaricus andSclerocephalus haeuseri, with the chronosubspeciesS. h. haeuseri andS. h. jeckenbachensis n. ssp., are redescribed based on material from the lower Rotliegend of the Saar-Nahe region (southern Germany). For the first time numerous features of the skull and postcranial skeleton as wellas the ontogenetic development of the skull are documented. The evolution of these species is discussed.     

Scaling of limb joint surface areas in anthropoid primates and other mammals

Recently it was reported that limb joint surface areas scale positively allometrically with body weight in anthropoid primates. This was attributed to the biomechanics of weight bearing: larger animals must require relatively larger joint surfaces to withstand relatively greater weight-related stresses on the joints. Our data on humeral and femoral geometry and joint surface areas in 73 species belonging to six mammalian orders (including primates) demonstrate that positive allometry of joint surface areas is not a general phenomenon for mammals and cannot have its basis among Anthropoidea in the biomechanics of weight bearing. We argue that, to the extent that positive allometric scaling of joint surface areas occurs in anthropoid primates, it is an artifact of differences in positional behaviour among distinct taxonomic groups that also happen to differ widely in body weight. Furthermore, we argue that, among mammals ranging in body size from sportive lemurs to giant pandas, functionally similar groups tend to exhibit: (1) linear dimensions (especially diameters and shaft circumferences) that scale in direct proportion to each other; and (2) joint surface areas that scale in direct proportion to the squares of linear dimensions and to the 2/3 power of body mass. In other words, limb bones of functionally similar animals fit the theoretical model of geometric similarity (or skeletal isometry). Differences in relative sizes of joint surface areas are related to differences in force transmission and movement potential among functionally distinct groups of animals.     

Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System

We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m^-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root     

Phenotypic and genetic differentiation between diadromous and landlocked puyen Galaxias maculatus

This study reports the phenotypic and genetic differences between individuals of puyen Galaxias maculatus from two sites in the same river basin in Tierra del Fuego National Park, southern South America. Individuals from the two sampling sites presented morphometric and genetic differences. The morphometric differences indicated that individuals from Laguna Negra (LN) were short and more robust and had large eyes, whereas those from Arroyo Negro (AN) were thin and elongated and had small eyes. Genetic differences showed that AN individuals had a greater genetic structuration and an older demographic history than LN individuals. The results of this study affirmed that the individuals from the two sampling sites belong to different populations with a high degree of isolation. The demographic history could indicate that the individuals of G. maculatus which migrated to northern areas during the last glaciation settled in the Beagle Channel after its formation. The LN population could have originated after the retreat of the glaciers, migrating from AN.     

“Enzyme Test Bench,” a high‐throughput enzyme characterization technique including the long‐term stability

A new high throughput technique for enzyme characterization with specific attention to the long term stability, called “Enzyme Test Bench,” is presented. The concept of the Enzyme Test Bench consists of short term enzyme tests in 96‐well microtiter plates under partly extreme conditions to predict the enzyme long term stability under moderate conditions. The technique is based on the mathematical modeling of temperature dependent enzyme activation and deactivation. Adapting the temperature profiles in sequential experiments by optimal non‐linear experimental design, the long term deactivation effects can be purposefully accelerated and detected within hours. During the experiment the enzyme activity is measured online to estimate the model parameters from the obtained data. Thus, the enzyme activity and long term stability can be calculated as a function of temperature. The engineered instrumentation provides for simultaneous automated assaying by fluorescent measurements, mixing and homogenous temperature control in the range of 10–85 ± 0.5°C. A universal fluorescent assay for online acquisition of ester hydrolysis reactions by pH‐shift is developed and established. The developed instrumentation and assay are applied to characterize two esterases. The results of the characterization, carried out in microtiter plates applying short term experiments of hours, are in good agreement with the results of long term experiments at different temperatures in 1 L stirred tank reactors of a week. Thus, the new technique allows for both: the enzyme screening with regard to the long term stability and the choice of the optimal process temperature regarding such process parameters as turn over number, space time yield or optimal process duration. The comparison of the temperature dependent behavior of both characterized enzymes clearly demonstrates that the frequently applied estimation of long term stability at moderate temperatures by simple activity measurements after exposing the enzymes to elevated temperatures may lead to suboptimal enzyme selection. Thus, temperature dependent enzyme characterization is essential in primary screening to predict its long term behavior. Biotechnol. Bioeng. 2009;103: 305–322. © 2008 Wiley Periodicals, Inc.     

The relA locus and the regulation of lysine biosynthesis in Escherichia coli

Summary The allelic state of relA influences the phenotype of Escherichia coli strains carrying the lysA22 mutation: lysA22 relA strains are Lys^– where lysA22 relA ⁺ strains grow (slowly) in the absence of lysine. This physiological effect has been related to an effect of the expression of the relA locus on the regulation of lysine biosynthesis. The fully derepressed levels of some lysine enzymes (aspartokinase III, aspartic semialdehyde dehydrogenase, dihydrodipicolinate reductase) are observed under lysine limitation only in rel ⁺ strains. And the induction of DAP-decarboxylase by DAP is much higher in rel ⁺ than in rel ^– strains when an amino acid limitation of growth is also realised. These results are in agreement with the hypothesis of Stephens et al. (1975) on a possible role of the stringent regulation as a general signal for amino acid deficiency.