The avian community of montane coniferous forests changed substantially over 21 years in response to the introduction of the balsam woolly adelgid insect ( Adelges piceae ) and the resulting death of endemic Fraser fir trees ( Abies fraseri ). These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid. At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data from Mount Collins showed that the combined density for all breeding birds also declined by half. Of the common territorial species present in 1974, 10 of 11 declined, 6 by more than 50%. Some species are near local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges, where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smoky Mountains appear to have buffered the effects of forest decline on the bird community. Respuesta de Comunidades de Aves a Perturbaciones de un Insecto Exótico en Bosques de Abeto en el Sur de los Apalaches Resumen: La comunidad de aves de bosques coníferos de montaña cambió sustancialmente a lo largo de 21 años en respuesta a la introducción del insecto adélgido lanudo Aldeges piceae y a la resultante muerte de árboles de Abetos Fraser ( Abies fraseri ). Estos vestigios de bosques se encuentran al limite sureño de su distribución en las montañas mas altas de los Apalaches. Combinamos un estudio histórico del monte Collins en las montañas Great Smoky con una comparación geográfica de sitios entre cinco cordilleras de los Apalaches afectados en forma variable por el adélgido. En el monte Collins, los abetos fueron virtualmente eliminados y la covertura del dosel reducida a la mitad de su nivel previo. Datos de largo plazo del monte Collins mostraron que la densidad combinada para todas las especies de aves anidando también disminuyó a la mitad.De las especies comunes en el territorio en 1974, 10 de 11 disminuyeron, seis en mas de un 50%. Algunas especies se encuentran cerca de su extinción local. Especies forrajeras de dosel y sub-dosel disminuyeron mas que aquellas especies forrajera...
The avian community of montane coniferous forests changed substantially over 21 years in response to the introduction of the balsam woolly adelgid insect ( Adelges piceae ) and the resulting death of endemic Fraser fir trees ( Abies fraseri ). These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid. At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data from Mount Collins showed that the combined density for all breeding birds also declined by half. Of the common territorial species present in 1974, 10 of 11 declined, 6 by more than 50%. Some species are near local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges, where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smoky Mountains appear to have buffered the effects of forest decline on the bird community. Respuesta de Comunidades de Aves a Perturbaciones de un Insecto Exótico en Bosques de Abeto en el Sur de los Apalaches Resumen: La comunidad de aves de bosques coníferos de montaña cambió sustancialmente a lo largo de 21 años en respuesta a la introducción del insecto adélgido lanudo Aldeges piceae y a la resultante muerte de ár-boles de Abetos Fraser ( Abies fraseri ). Estos vestigios de bosques se encuentran al limite sureño de su distribución en las montañas mas altas de los Apalaches. Combinamos un estudio histórico del monte Collins en las montañas Great Smoky con una comparación geográfica de sitios entre cinco cordilleras de los Apalaches afectados en forma variable por el adélgido. En el monte Collins, los abetos fueron virtualmente eliminados y la covertura del dosel reducida a la mitad de su nivel previo. Datos de largo plazo del monte Collins mostraron que la densidad combinada para todas las especies de aves anidando también disminuyó a la mitad.De las especies comunes en el territorio en 1974, 10 de 11 disminuyeron, seis en mas de un 50%. Algunas especies se encuentran cerca de su extinción local. Especies forrajeras de dosel y sub-dosel disminuyeron mas que aquellas especies forrajer...
We constructed plasmids carrying the Escherichia coli proB gene that encodes gamma-glutamyl kinase, under the control of the yeast GAL1 promoter. This construction was carried out with both the wild-type proB+ gene and a mutant allele, proB74, that specifies an enzyme resistant to feedback inhibition by proline. Yeast pro1 mutants harboring these plasmids are proline prototrophs. We conclude that the pro1 mutation results in a deficiency in the gamma-glutamyl kinase activity in Saccharomyces cerevisiae. Expression of the proB74 allele in yeast resulted in enhanced resistance to the proline analogue L-azetidine-2-carboxylate and in a 2.4-fold elevation of the intracellular free proline levels. This result suggests that gamma-glutamyl kinase is the rate limiting step in proline biosynthesis in yeast.
Background The halophilic bacterium Chromohalobacter salexigens metabolizes glucose exclusively through the Entner–Doudoroff (ED) pathway, an adaptation which results in inefficient growth, with significant carbon overflow, especially at low salinity. Preliminary analysis of C. salexigens genome suggests that fructose metabolism could proceed through the Entner–Doudoroff and Embden–Meyerhof–Parnas (EMP) pathways. In order to thrive at high salinity, this bacterium relies on the biosynthesis and accumulation of ectoines as major compatible solutes. This metabolic pathway imposes a high metabolic burden due to the consumption of a relevant proportion of cellular resources, including both energy molecules (NADPH and ATP) and carbon building blocks. Therefore, the existence of more than one glycolytic pathway with different stoichiometries may be an advantage for C. salexigens. The aim of this work is to experimentally characterize the metabolism of fructose in C. salexigens . Results Fructose metabolism was analyzed using in silico genome analysis, RT-PCR, isotopic labeling, and genetic approaches. During growth on fructose as the sole carbon source, carbon overflow was not observed in a wide range of salt concentrations, and higher biomass yields were reached. We unveiled the initial steps of the two pathways for fructose incorporation and their links to central metabolism. While glucose is metabolized exclusively through the Entner–Doudoroff (ED) pathway, fructose is also partially metabolized by the Embden–Meyerhof–Parnas (EMP) route. Tracking isotopic label from [1- 13 C] fructose to ectoines revealed that 81% and 19% of the fructose were metabolized through ED and EMP-like routes, respectively. Activities of enzymes from both routes were demonstrated in vitro by 31 P-NMR. Genes encoding predicted fructokinase and 1-phosphofructokinase were cloned and the activities of their protein products were confirmed. Importantly, the protein encoded by csal1534 gene functions as fructose bisphosphatase, although it had been annotated previously as pyrophosphate-dependent phosphofructokinase. The gluconeogenic rather than glycolytic role of this enzyme in vivo is in agreement with the lack of 6-phosphofructokinase activity previously described. Conclusions Overall, this study shows that C. salexigens possesses a greater metabolic flexibility for fructose catabolism, the ED and EMP pathways contributing to a fine balancing of energy and biosynthetic demands and, subsequently, to a more efficient metabolism. Electronic supplementary material The online version of this article (10.1186/s12934-019-1178-x) contains supplementary material, which is available to authorized users.
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