The population-dynamic functions of seed dispersal

We summarize some of the population-dynamic consequences of the mosaic structure of plant populations for the evolution of seed dispersal. A fairly elaborated set of theoretical ideas exist regarding the evolution of dispersal and we have synthesized some of them in an attempt to make them more accessible to field ecologists. We consider the relationship of these general theoretical ideas to our understanding of fruit and seed dispersal.We develop three related models to describe the similarities and differences in how dispersal functions for risk reduction (bet hedging), escaping the negative consequences of crowding, and escaping high concentrations of relatives. We also briefly discuss directed dispersal as a fourth population-dynamic aspect of dispersal. Dispersal can have a risk-reducing function only when there is global (metapopulation) temporal variance in success. Dispersal to escape the negative consequences of crowding requires only spatial and local temporal environmental variation. Dispersal for escaping high concentrations of relatives requires no environmental variation, but does require genetic population structure. Directed dispersal, defined as non-random into particular patch types contingent on the expectation of local success, is always valuable when possible and represents an advantage independent the others which can occur with random dispersal.In an effort to accommodate for the differences between simple mathematical models and the behavior of complex natural fruit and seed dispersal systems we have discussed the following issues: actual patterns of patch structure and dispersal distance; the implications of plant cosexuality, perenniality, and allocation costs of dispersal structures; and the impact of the detailed nature of density dependence, breeding systems, and genetic structure. We briefly compare the population-dynamic functions of dispersal presented here with the widely cited functions of colonization, escape, and directed dispersal. Finally, we suggest how the theoretical models can be used with field data to estimate the fitness consequences of dispersal.     

Synthetic chimeras of mouse growth factor-associated glandular kallikreins. I. Kinetic properties.

A series of six chimeric proteins, composed of fragments corresponding to either one or the other of the growth factor-associated mouse glandular kallikreins-epidermal growth factor binding protein (EGF-BP) and the gamma-subunit of nerve growth factor (gamma-NGF)--were expressed in Escherichia coli and isolated, and their kinetic properties were characterized. The assembly of these synthetic proteases involved the substitution of regions of the proteins containing four specific surface loops that have been postulated to influence both kinetic specificity and the formation of growth factor complexes. The substrates utilized in the kinetic characterization of these chimeric kallikreins were tripeptide nitroanilides representing carboxyl termini of both the EGF and beta-NGF mature hormones, putative processing sites for these kallikreins in the precursors. Characterization of these hybrid enzymes demonstrates that Km and kcat kinetic constants may be independently affected by the regions utilized in construction of these chimeric kallikreins. Specifically, loop 1, located in the amino terminal region (Bode, W., et al., J. Mol. Biol. 164, 237-282, 1983), in gamma-NGF enhanced the kcat for substrates containing threonine in the P2 position, as is the case during the processing of the carboxy terminus of the beta-NGF precursor. Also, the central regions of the kallikreins containing loop 2 and the kallikrein loop dictated the generally inverted Km and kcat kinetic constants observed between EGF-BP and gamma-NGF. Finally, in gamma-NGF the autolysis loop, found in the carboxyl terminal region, functions to lower the Km kinetic constant for a variety of substrates. The results allow previously characterized kinetic differences between EGF-BP and gamma-NGF to be interpreted in terms of specific regions of the proteins and identify a subset of amino acid positions responsible for these functional characteristics.     

壳聚糖酶结构与功能的研究进展

壳聚糖酶是一类对壳聚糖具有较高催化活性而几乎不水解几丁质的糖苷水解酶,其可将高分子量的壳聚糖转化为低分子量的功能性壳寡糖。近年来,对壳聚糖酶的相关研究取得了显著进展,因此,本文对其生化性质、晶体结构、催化机制和蛋白质工程改造进行总结和探讨,并对酶法制备壳寡糖纯品进行展望,这将加深研究者对壳聚糖酶作用机制的认识,推动壳聚糖酶的工业应用。     

Dynamic genome-scale modeling of Saccharomyces cerevisiae unravels mechanisms for ester formation during alcoholic fermentation

Fermentation employing Saccharomyces cerevisiae has produced alcoholic beverages and bread for millennia. More recently, S. cerevisiae has been used to manufacture specific metabolites for the food, pharmaceutical, and cosmetic industries. Among the most important of these metabolites are compounds associated with desirable aromas and flavors, including higher alcohols and esters. Although the physiology of yeast has been well-studied, its metabolic modulation leading to aroma production in relevant industrial scenarios such as winemaking is still unclear. Here we ask what are the underlying metabolic mechanisms that explain the conserved and varying behavior of different yeasts regarding aroma formation under enological conditions? We employed dynamic flux balance analysis (dFBA) to answer this key question using the latest genome-scale metabolic model (GEM) of S. cerevisiae. The model revealed several conserved mechanisms among wine yeasts, for example, acetate ester formation is dependent on intracellular metabolic acetyl-CoA/CoA levels, and the formation of ethyl esters facilitates the removal of toxic fatty acids from cells using CoA. Species-specific mechanisms were also found, such as a preference for the shikimate pathway leading to more 2-phenylethanol production in the Opale strain as well as strain behavior varying notably during the carbohydrate accumulation phase and carbohydrate accumulation inducing redox restrictions during a later cell growth phase for strain Uvaferm. In conclusion, our new metabolic model of yeast under enological conditions revealed key metabolic mechanisms in wine yeasts, which will aid future research strategies to optimize their behavior in industrial settings.     

Anti-CRISPR Discovery: Using Magnets to Find Needles in Haystacks

CRISPR-Cas immune systems in bacteria and archaea protect against viral infection, which has spurred viruses to develop dedicated inhibitors of these systems called anti-CRISPRs (Acrs). Like most host-virus arms races, many diverse examples of these immune and counter-immune proteins are encoded by the genomes of bacteria, archaea, and their viruses. For the case of Acrs, it is almost certain that just a small minority of nature’s true diversity has been described. In this review, I discuss the various approaches used to identify these Acrs and speculate on the future for Acr discovery. Because Acrs can determine infection outcomes in nature and regulate CRISPR-Cas activities in applied settings, they have a dual importance to both host-virus conflicts and emerging biotechnologies. Thus, revealing the largely hidden world of Acrs should provide important lessons in microbiology that have the potential to ripple far beyond the field.     

Nitrogen and energy losses and methane emissions from beef cattle fed diets with gradual replacement of maize silage and concentrate with grass silage and corn-cob mix

Diets based on large proportions of grassland-based feed are uncommon in forage-based intensive beef production, thus contradicting governmental or commercial strategies to promote the use of grassland-based feed in ruminant production systems. Compared with typical maize silage/concentrate diets, grassland-based diets are associated with impaired nitrogen (N) and energy utilisation because of the comparably lower energy and higher CP content of these feeds. However, quantitative studies concerning the effects of increased dietary proportions of grassland-derived feeds on N and energy losses and utilisation and on methane emissions are missing and the compensation potential of using a limited proportion of an energy-rich forage is unknown. Therefore, we tested five diets with varying types and proportions of forage and concentrate. Three diets consisted of grass silage, maize silage, and concentrate in ratios of, g/kg DM, 100:600:300 (G100; control), 300:500:200 (G300), and 500:300:200 (G500), respectively. Two diets were composed of grass silage, corn-cob mix (CCM), and concentrate in ratios of, g/kg DM, 500:300:200 (G500_CCM), and 750:150:100 (G750_CCM), respectively. A high-protein concentrate (270 g CP/kg DM) was fed to G100, whereas a low-protein concentrate (140 g CP/kg DM) was used in the remaining diets. Diets were fed throughout the entire fattening period to groups of six Limousin-crossbred bulls each. When weighing 246 ± 18 kg, each animal underwent a 7-day total daily faeces and urine collection, which was followed by measuring methane emissions in respiration chambers for 48 h. Total DM intake was similar across all diets, whereas the N intake varied (P < 0.05). Urinary N loss (g/day) was the highest for G750_CCM (28.2) and G100 (26.6) and lowest for G500_CCM (15.2) and G300 (16.9) (P < 0.001). Energy utilisation was comparable among all groups. Metabolisable energy intake decreased numerically only with increasing proportions of grass silage in the diet. Substituting maize silage with CCM counteracted the loss in metabolisable energy intake. Absolute methane emissions were not different across the groups, but methane emission intensity (mg/g body protein retention) varied (P < 0.05), being numerically lower for G100 (349) and G500_CCM (401) compared with the other groups (488 on average). In conclusion, the results show that the grass silage proportion in beef cattle diets can be substantially increased when strategically combined with energy-dense forages, such as CCM. This also limits the need for concentrate and additional protein sources; in addition, the associated urinary N emissions, which are potentially noxious to the environment, are avoided.     

GENETIC EVIDENCE FOR MULTIPLE ORIGINS OF DIOECY IN THE HAWAIIAN SHRUB WIKSTROEMIA (THYMELAEACEAE)

Dioecy is unusually common in the Hawaiian Islands, yet little is known about the evolutionary biology of this breeding system. A native shrub, Wikstroemia, has an unusually diverse array of breeding systems: two forms of dioecy, cryptic and morphological dioecy, as well as hermaphroditism (perfect flowers). The existence of two forms of dioecy is significant for three reasons: 1) the presence of cryptic unisexuals that are functionally unisexual, but retain the appearance of hermaphroditism in both sexes, is strong evidence for the ancestral status of hermaphroditism; 2) the production of nonfunctional pollen, by female cryptic unisexuals, is a new instance of a phenomenon which has previously been reported for a few other species; 3) the two forms of dioecy are morphological markers which are useful in hybridization studies for tracing the genetic basis of their inheritance. Crosses were made between cryptically unisexual individuals (C), between morphologically unisexual individuals (M), and between the two types of unisexuality. The offspring of crosses between individuals with the same sex type usually resulted in offspring with that sex type, but most of the progeny of between-sex type crosses were, unexpectedly, perfect-flowered hermaphrodites. These results show that genetic control of sex determination is not homologous in all populations, suggesting that dioecy has evolved at least twice in Hawaiian Wikstroemia. The genetic data further suggest that males are the heterozygous sex.     

Impact of cell disruption and polymer recycling upon aqueous two-phase processes for protein recovery

A practical study is presented of the influence of cell debris and polymer recycling upon the operation of two-stage acqueous two-phase systems (ATPS) for the recovery of yeast bulk protein, pyruvate kinase and fumarase. Brewers' yeast was disrupted using one of two types of high-pressure homogenisers or a bead mill. The different cell debris suspensions were partitioned in a single PEG-phosphate ATPS extraction and the efficiency of solid-liquid separation was examined. A continuously operated two-stage ATPS process, using spray columns, is presented and practical problems of polymer recycling are discussed. Conclusions are drawn concerning the generic implementation and operational stability of ATPS in practical protein recoveries.     

多组多滞后区间系数定常非线性关联控制大系统的结构与关联鲁棒镇定(I)

建立了多组多滞后区间系数定常非线性控制系统的结构概念,采用鲁棒镇定的等价法,给出了具有扰动结构参数的多组多滞后区问系数定常非线性关联控制大系统的结构与关联鲁棒镇定,同时给出了扰动参数与滞后非线性项界线的估价公式。