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"Collins, L"
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Bile acids and the gut microbiota: metabolic interactions and impacts on disease
Despite decades of bile acid research, diverse biological roles for bile acids have been discovered recently due to developments in understanding the human microbiota. As additional bacterial enzymes are characterized, and the tools used for identifying new bile acids become increasingly more sensitive, the repertoire of bile acids metabolized and/or synthesized by bacteria continues to grow. Additionally, bile acids impact microbiome community structure and function. In this Review, we highlight how the bile acid pool is manipulated by the gut microbiota, how it is dependent on the metabolic capacity of the bacterial community and how external factors, such as antibiotics and diet, shape bile acid composition. It is increasingly important to understand how bile acid signalling networks are affected in distinct organs where the bile acid composition differs, and how these networks impact infectious, metabolic and neoplastic diseases. These advances have enabled the development of therapeutics that target imbalances in microbiota-associated bile acid profiles.The gut microbiota metabolizes bile acids, thereby influencing human health and diseases including obesity, colitis and cancer. In this Review, Patterson and colleagues discuss host–microbiota interactions and their influence on the bile acid pool as well as therapeutic implications.
Journal Article
Legacy : relics of Mars
Now in seventh grade Belle Song has settled into her life on Mars; she has a new baby sister, her android Melody, her wolfdog Raider, and her friends, the human Lucas, and the Nabian, Taal--but when she and Taal uncover some ancient ruins which the Nabians claim are a sacred site, Belle finds herself plunged into a tricky world of extraterrestrial politics and religion that threatens her relationship with Taal.
Book
Interactive effects of grazing, drought, and fire on grassland plant communities in North America and South Africa
Grazing, fire, and climate shape mesic grassland communities. With global change altering all three factors, understanding how grasslands respond to changes in these combined drivers may aid in projecting future changes in grassland ecosystems. We manipulated rainfall and simulated grazing (clipping) in two long-term fire experiments in mesic grasslands in North America (NA) and South Africa (SA). Despite their common drivers, grasslands in NA and SA differ in evolutionary history. Therefore, we expected community structure and production in NA and SA to respond differently to fire, grazing, and drought. Specifically, we hypothesized that NA plant community composition and production would be more responsive than the SA plant communities to changes in the drivers and their interactions, and that despite this expected stability of SA grasslands, drought would be the dominant factor controlling production, but grazing would play the primary role in determining community composition at both sites. Contrary to our hypothesis, NA and SA grasslands generally responded similarly to grazing, drought, and fire. Grazing increased diversity, decreased grass cover and production, and decreased belowground biomass at both sites. Drought alone minimally impacted plant community structure, and we saw similar treatment interactions at the two sites. Drought was not the primary driver of grassland productivity, but instead drought effects were similar to or less than grazing and fire. Even though these grasslands differed in evolutionary history, they responded similarly to our fire, grazing, and climate manipulations. Overall, we found community and ecosystem convergence in NA and SA grasslands. Grazing and fire are as important as climate in controlling mesic grassland ecosystems on both continents.
Journal Article
Homestead : a new life on Mars
Twelve-year-old Belle Song and her family moved to Mars because they were offered good jobs, only to find that the jobs have disappeared--her father, Yun, is unwilling to return to the worn-out Earth, so, to the horror of his city-raised daughter, he buys a farm in the \"Wild West\" area of Mars, and Belle does her best to adapt to a life which is filled with difficulties and danger.
Book
Woody encroachment decreases diversity across North American grasslands and savannas
Woody encroachment is a widespread and acute phenomenon affecting grasslands and savannas worldwide. We performed a meta-analysis of 29 studies from 13 different grassland/savanna communities in North America to determine the consequences of woody encroachment on plant species richness. In all 13 communities, species richness declined with woody plant encroachment (average decline = 45%). Species richness declined more in communities with higher precipitation (
r
2
= 0.81) and where encroachment was associated with a greater change in annual net primary productivity (ANPP;
r
2
= 0.69). Based on the strong positive correlation between precipitation and ANPP following encroachment (
r
2
= 0.87), we hypothesize that these relationships occur because water-limited woody plants experience a greater physiological and demographic release as precipitation increases. The observed relationship between species richness and ANPP provides support for the theoretical expectation that a trade-off occurs between richness and productivity in herbaceous communities. We conclude that woody plant encroachment leads to significant declines in species richness in North American grassland/savanna communities.
Journal Article
A chemically powered unidirectional rotary molecular motor based on a palladium redox cycle
The conversion of chemical energy to drive directional motion at the molecular level allows biological systems, ranging from subcellular components to whole organisms, to perform a myriad of dynamic functions and respond to changes in the environment. Directional movement has been demonstrated in artificial molecular systems, but the fundamental motif of unidirectional rotary motion along a single-bond rotary axle induced by metal-catalysed transformation of chemical fuels has not been realized, and the challenge is to couple the metal-centred redox processes to stepwise changes in conformation to arrive at a full unidirectional rotary cycle. Here, we present the design of an organopalladium-based motor and the experimental demonstration of a 360° unidirectional rotary cycle using simple chemical fuels. Exploiting fundamental reactivity principles in organometallic chemistry enables control of directional rotation and offers the potential of harnessing the wealth of opportunities offered by transition-metal-based catalytic conversions to drive motion and dynamic functions.
Control of motion at the molecular level is an integral requirement for the development of future nanoscale machinery. Now, governed by the fundamental reactivity principles of organometallic chemistry, a biaryl rotor is shown to exhibit 360° unidirectional rotary motion driven by the conversion of two simple fuels.
Journal Article