The role of volumetric power input in the growth,morphology, and production of a recombinant glycoprotein by Streptomyces lividans in shake flasks

The impact of flask geometry on Streptomyces lividans growth and morphology, production and O-mannosylation of a recombinant O-glycoprotein (APA from Mycobacterium tuberculosis) was described and associated to the evolution of the volumetric power input (P/V) in three shake flask geometries. During the exponential growth, the highest P/V was found in baffled flasks (BF) with 0.51 kW/m³, followed by coiled flasks (CF) with 0.44 kW/m³ and normal Erlenmeyer flasks (NF) with 0.20 kW/m³ (flasks volume of 250 mL, filling with 50 mL and agitated at 150 rpm). During the stationary phase, P/V decreased 20% in BF and CF, but increased two times in NF, surely due to changes in mycelial morphology and its effects on rheology. Also, NF cultures were carried out at a filling volume and agitation of 15 mL, 150 rpm (15 mL-NF), and 25 mL, 168 rpm (25 mL-NF), in order to raise P/V closely to the values obtained in CF. However, different growth, morphology and recombinant protein productivity were obtained. These data indicate that P/V is not a definitive parameter that can determine bacteria growth and morphology, not even glycoprotein production. But it can be proposed that the oxygen transfer in the center of the pellets and hydromechanical stress might be the more relevant parameters than P/V.     

The phylogenetic placement of Psechridae within Entelegynae and the convergent origin of orb‐like spider webs

Evolutionary convergence of phenotypic traits provides evidence for their functional success. The origin of the orb web was a critical event in the diversification of spiders that facilitated a spectacular radiation of approximately 12 000 species and promoted the evolution of novel web types. How the orb web evolved from ancestral web types, and how many times orb‐like architectures evolved in spiders, has been debated for a long time. The little known spider genus Fecenia (Psechridae) constructs a web that resembles the archetypical orb web, but morphological data suggest that Psechridae (Psechrus + Fecenia) does not belong in Orbiculariae, the ‘true orb weavers’, but to the ‘retrolateral tibial apophysis (RTA) clade’ consisting mostly of wandering spiders, but also including spiders building less regular webs. Yet, the data are sparse and no molecular phylogenetic study has estimated Fecenia's exact position in the tree of life. Adding new data to sequences pulled from GenBank, we reconstruct a phylogeny of Entelegynae and phylogenetically test the monophyly and placement of Psechridae, and in doing so, the alternative hypotheses of monophyletic origin of the orb web and the pseudo‐orb versus their independent origins, a potentially spectacular case of behavioural convergence. We also discuss the implications of our results for Entelegynae systematics. Our results firmly place a monophyletic Psechridae within the RTA clade, phylogenetically distant from true orb weavers. The architectural similarities of the orb and the pseudo‐orb are therefore clearly convergent, as also suggested by detailed comparisons of these two web types, as well as the spiders' web‐building behaviours and ontogenetic development. The convergence of Fecenia webs with true orbs provides a remarkable opportunity to investigate how these complex sets of traits may have interacted during the evolution of the orb.     

Are Victoria West cores “proto-Levallois”? A phylogenetic assessment

Cores from South Africa assigned to the “Victoria West” industry have long been purported as a “proto-Levallois” core form, and thus regarded as ancestral to the Levallois prepared core technologies of the Middle Paleolithic and African Middle Stone Age. Similarities in form between Victoria West cores, in terms of surface morphology and the removal of large flakes from a prepared surface, led to hypothesized schemes of technological evolution from Victoria West cores through to fully developed Levallois cores. However, the phylogenetic basis of this Victoria West “proto-Levallois” hypothesis, and the assumptions of phylogenetic homology upon which it rests, have never been tested formally. In recent years, archaeologists have begun to use phylogenetic methods drawn from biology to test hypotheses of technological and cultural evolution. Here, the phylogenetic assumptions of the Victoria West “proto-Levallois” hypothesis are tested directly using a cladistic (maximum parsimony) protocol. The cladistic analyses indicate that Victoria West cores are not the basal sister taxon of a Levallois clade, as predicted by the proto-Levallois hypothesis. Moreover, character analyses demonstrate that several characters relating to core surfaces and flake scar morphology are not phylogenetically homologous, but result from convergent technological evolution within the Acheulean techno-complex. Post hoc analyses further determine that these results are not confounded by choice of outgroup or raw material factors. The results were also shown to be robust on the basis of the ensemble retention index statistic, bootstrap analyses, and permutation tests. Hence, it is concluded that Victoria West cores do not represent a “proto-Levallois” core form, and that the term “para-Levallois” should more correctly be applied on phylogenetic grounds. It is further argued that even in cases where different technologies are found to share phylogenetically homologous features, use of the term “proto” is questionable on theoretical grounds.     

Convergence rate estimation for the TKF91 model of biological sequence length evolution

The TKF91 model of biological sequence evolution describes changes in the sequence length via an infinite state-space birth-death process, which we term the TKF91-BD process. The TKF91 model assumes that, for any pair of modern sequences, the ancestral sequence has equilibrium length distribution, an assumption whose validity has not been rigorously investigated. We obtain explicit upper and lower bounds on the rate of convergence to equilibrium for the distribution of the TKF91-BD process. We show that the rate of convergence of the TKF91-BD process for protein sequences with parameter values inferred from sequence data on alpha and beta globins is too low to guarantee convergence to equilibrium on a reasonable timescale. For the analyzed nucleotide sequences, the convergence is faster, but the equilibrium sequence length is unrealistically small. The Jukes-Cantor model of nucleotide substitutions can converge considerably faster than the length evolution model for both amino acid and nucleotide sequences, while the speed of convergence for the Kimura model is close to that for the TKF91-BD process describing nucleotide sequences.     

Mechanoreceptor signal convergence and transformation in the dorsal horn flexibly shape a diversity of outputs to the brain

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The late Cenozoic Thiaridae (Mollusca, Gastropoda, Cerithioidea) of the Albertine Rift Valley (Uganda-Congo) and their bearing on the origin and evolution of the Tanganyikan thalassoid malacofauna

The recent cerithioid malacofauna of meromictic Lake Tanganyika is unique in its degree of thalassoid convergence with marine molluscs. This is generally considered the result of a long-lasting intensive escalation and cladogenesis caused by a coevolutionary prey–predator interaction in a freshwater ecosystem with sea-like characteristics, i.e. exceptional longevity (ca. 7–12 Ma) and vast dimensions (present surface area: 32900 km², present maximum depth: 1470 m). In the Albertine Basin, ca 300 km north of the Tanganyika Trough, Palaeolake Obweruka existed during Mio-Pliocene times. In many aspects, it can be considered as a 'sister lake' of Lake Tanganyika, being also long-lived (from ca 7.5 to 2.5 Ma), extensive (surface: 27000 km²) and meromictic. Like Lake Tanganyika it belonged to the Congo catchment. Although thalassoid molluscs have been known from the Albertine deposits since the beginning of the 20th Century, previous researchers recognised only four polymorphic thiarid species, two of which were thalassoid. Detailed in situ collecting shows that the perceived low species diversity and high variability of the Obwerukan thalassoids is a phenomenon of the museum drawer. In the field the thiarid species and other molluscs are not extremely polymorphic, as formerly thought, but tend to occur in discrete morphometric packages according to stratigraphic level and geographic area. The species richness of the Palaeolake Obweruka thiarids has thus been severely underestimated, as is also the case for the Recent Tanganyikan thiarids. The present authors discern 35 species and 7 genera in the Albertine deposits (2 of which are new to science), and consider this to be a conservative estimate. In their degree of diversification and morphological escalation, the Obwerukan thiarids are thus comparable to the Tanganyika thalassoids. Arguments are presented that the thalassoids of these lakes are polyphyletic, that they are derived from the same genera (mainly Potadoma, Potadomoides and Pseudocleopatra) and that the tempo and mode of their intralacustrine evolution must have been largely similar. As for the tempo of evolution, the Albertine fossil record shows that escalation in shell morphology and ornamentation in the Thiaridae was extremely rapid, as in the Ampullariidae and Viviparidae (Van Damme & Pickford, 1995, 1999). In the Thiaridae heavily ornate shells evolved from an unornamented ancestor in two consecutive bursts, each lasting less than 0.1 million years over a total period of ca. 1 million years. The punctuated escalation in the thiarids was initiated millions of years after the lake was formed. This implies that the degree of escalation is not related to age of a lake and that the Tanganyikan thalassoids or part of them may not be particularly old, even though Lake Tanganyika itself is. As to the mode of evolution, it appears that escalation is a coevolutionary reaction to predation but that this selective pressure only triggers a reaction under specific conditions and in synergy with other environmental factors. The Obwerukan thiarid fossil record also indicates that iterative evolution of molluscan shells may be of frequent occurrence. What is considered to be a single polymorphic chronospecies, static over a great length of time, may actually be a sequence of several species that branched at different moments from the same ancestral phenotype. Finally, there is the inference that bottle-necking may be, geologically speaking, so common that it forms an essential force in macroevolution.     

Coalescent patterns in diploid exchangeable population models

A class of two-sex population models is considered with N females and equal number N of males constituting each generation. Reproduction is assumed to undergo three stages: 1) random mating, 2) exchangeable reproduction, 3) random sex assignment. Treating individuals as pairs of genes at a certain locus we introduce the diploid ancestral process (the past genealogical tree) for n such genes sampled in the current generation. Neither mutation nor selection are assumed. A convergence criterium for the diploid ancestral process is proved as N goes to infinity while n remains unchanged. Conditions are specified when the limiting process (coalescent) is the Kingman coalescent and situations are discussed when the coalescent allows for multiple mergers of ancestral lines.Work supported by the Bank of Sweden Tercentenary Foundation.Mathematics Subject Classification (2000):Primary 92F25, 60J70; Secondary 92D15, 60F17     

低频电流场颅内异物检测技术重建算法的研究

电磁场数值计算方法可用于检测颅内异物。使用的重建算法有拟牛顿法、Bulirsch-Stoer外推法、局部加速收敛法。这些算法对改善重建计算的精度起着至关重要的作用。最后,仿真计算说明算法是有效的。