Penitentes as the origin of the bladed terrain of Tartarus Dorsa on Pluto.

Penitentes are snow and ice features formed by erosion that, on Earth, are characterized by bowl-shaped depressions several tens of centimetres across, whose edges grade into spires up to several metres tall. Penitentes have been suggested as an explanation for anomalous radar data on Europa, but until now no penitentes have been identified conclusively on planetary bodies other than Earth. Regular ridges with spacings of 3,000 to 5,000 metres and depths of about 500 metres with morphologies that resemble penitentes have been observed by the New Horizons spacecraft in the Tartarus Dorsa region of Pluto (220°-250° E, 0°-20° N). Here we report simulations, based upon a recent model representing conditions on Pluto, in which deepening penitentes reproduce both the tri-modal (north-south, east-west and northeast-southwest) orientation and the spacing of the ridges of this bladed terrain. At present, these penitentes deepen by approximately one centimetre per orbital cycle and grow only during periods of relatively high atmospheric pressure, suggesting a formation timescale of several tens of millions of years, consistent with crater ages. This timescale implies that the penitentes formed from initial topographic variations of no more than a few tens of metres, consistent with Pluto's youngest terrains.

Engineered Orthogonal Quorum Sensing Systems for Synthetic Gene Regulation in Escherichia coli.

Gene regulators that are controlled by membrane-permeable compounds called homoserine lactones (HSLs) have become popular tools for building synthetic gene networks that coordinate behaviors across populations of engineered bacteria. Synthetic HSL-signaling systems are derived from natural DNA and protein elements from microbial quorum signaling pathways. Crosstalk, where a single HSL can activate multiple regulators, can lead to faults in networks composed of parallel signaling pathways. Here, we report an investigation of quorum sensing components to identify synthetic pathways that exhibit little to no crosstalk in liquid and solid cultures. In previous work, we characterized the response of a single regulator (LuxR) to 10 distinct HSL-synthase enzymes. Our current study determined the responses of five different regulators (LuxR, LasR, TraR, BjaR, and AubR) to the same set of synthases. We identified two sets of orthogonal synthase-regulator pairs (BjaI/BjaR + EsaI/TraR and LasI/LasR + EsaI/TraR) that show little to no crosstalk when they are expressed in Escherichia coli BL21. These results expand the toolbox of characterized components for engineering microbial communities.

Background levels of methane in Mars' atmosphere show strong seasonal variations.

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

Mechanisms of acetylcholine-mediated vasodilation in systemic arteries from mourning doves (Zenaida macroura).

For mammals, acetylcholine (ACh) promotes endothelium-dependent vasodilation primarily through nitric oxide (NO) and prostaglandin-mediated pathways, with varying reliance on endothelial-derived hyperpolarizing factors. Currently, no studies have been conducted on small systemic arteries from wild birds. We hypothesized that ACh-mediated vasodilation of isolated small arteries from mourning doves (Zenaida macroura) would likewise depend on endothelial-derived factors. Small resistance mesenteric and cranial tibial (c. tibial) arteries (80-150 µm, inner diameter) were cannulated and pre-constricted to 50 % of resting inner diameter with phenylephrine then exposed to increasing concentrations of ACh (10(-9)-10(-5) M) or the NO donor, sodium nitroprusside (SNP; 10(-12)-10(-3) M). For mesenteric arteries, ACh-mediated vasodilation was significantly blunted with the potassium channel antagonist tetraethylammonium chloride (TEA, 10 mM); whereas responses were only moderately impaired with endothelial disruption or inhibition of prostaglandins (indomethacin, 10 µM). In contrast, endothelial disruption as well as exposure to TEA largely abolished vasodilatory responses to ACh in c. tibial arteries while no effect of prostaglandin inhibition was observed. For both vascular beds, responses to ACh were moderately dependent on the NO signaling pathway. Inhibition of NO synthase had no impact, despite complete reversal of phenylephrine-mediated tone with SNP, whereas inhibition of soluble guanylate cyclase (sGC) caused minor impairments. Endothelium-independent vasodilation also relied on potassium channels. In summary, ACh-mediated vasodilation of mesenteric and c. tibial arteries occurs through the activation of potassium channels to induce hyperpolarization with moderate reliance on sGC. Prostaglandins likewise play a small role in the vasodilatory response to ACh in mesenteric arteries.

Naturally high plasma glucose levels in mourning doves (Zenaida macroura) do not lead to high levels of reactive oxygen species in the vasculature.

Plasma glucose (P(Glu)) concentrations in birds are 1.5-2 times higher than those of mammals of similar body mass. In mammals, sustained elevations of P(Glu) lead to oxidative stress and free radical-mediated scavenging of endogenous vasodilators (e.g., nitric oxide), contributing to elevated blood pressure. Despite the relatively high P(Glu) levels in birds, they appear resistant to the development of oxidative stress in tissues such as the heart, brain and kidneys. To our knowledge no information exists on oxidative stress susceptibility in the resistance vasculature of birds. Therefore, we compared endogenous antioxidant mechanisms in the resistance vasculature of mourning doves (MODO; Zenaida macroura) and rats (Rattus norvegicus). Reactive oxygen species (ROS) were assessed with the fluorescent indicator 7'-dichlorodihydrofluorescein diacetate, acetyl ester in mesenteric arteries from rats and wild-caught MODO. Despite having significantly higher P(Glu) than rats, there were no significant differences in ROS levels between mesenteric arteries from rats or doves. Although superoxide dismutase and catalase activities were lower in the plasma, total antioxidant capacity, uric acid, vitamin E (α-tocopherol), and carotenoids (lutein and zeaxanthin) were significantly higher in MODO than in rats. Thus, compared to rats, MODO have multiple circulating antioxidants that may prevent the development of oxidative stress in the vasculature.