Uranium isotopes fingerprint biotic reduction

Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.The search for a tool to discriminate biotic from abiotic processes principally triggered the investigation of isotope fractionation of metals through redox processes (1). Several prerequisites must be fulfilled in order for the isotope fractionation of a metal to represent an appropriate redox biosignature: (i) the geochemistry of the metal must include at least one biologically catalyzed reaction (e.g., biological oxidation or reduction); (ii) the transformation must result in immobilization of the metal and its isotopic fractionation; (iii) there must be a difference in isotopic signature between biotic and abiotic transformation; and (iv) the reaction must not go to completion (as quantitative conversion of reactants to product suppresses isotopic fractionation).As demonstrated in this study, the radionuclide uranium (U) fulfills these requirements. Its mobility and deposition in low-temperature environments is controlled by redox transitions (2). The oxidized form [U(VI)] is largely soluble in the aqueous phase, whereas the reduced form [U(IV)] is sparingly soluble and precipitates, leading to U deposition under reducing conditions (3, 4). There are numerous pathways for U(VI) reduction, including direct biotic transformation mediated by metabolically varied microorganisms such as sulfate-reducing, iron-reducing, and fermenting bacteria (2), as well as abiotic reduction by redox-active minerals and solutes such as Fe(II)- or sulfide-bearing minerals, aqueous Fe(II), and sulfide species, as well as organic compounds (5–7).Moreover, permil-level fractionations of the two abundant and primordial uranium isotopes are reported in association with U(VI) to U(IV) redox transitions through the accumulation of the heavy isotope (²³⁸U) rather than the light isotope (²³⁵U) in the reduced product (8–13). This isotopic signature has been measured in low-temperature paleo-environments, enabling the use of U isotope fractionation as a proxy for the redox conditions of ancient atmosphere and oceans (14–16). A recent study (17) observed enrichment of the heavier ²³⁸U isotope in the products of biogenic U reduction, consistent with findings in nature (8, 10, 11, 18) and in agreement with ab initio calculations (19, 20).Hence, the major remaining question is whether biotic reduction of U results in an exclusive and distinct isotopic signature, readily distinguishable from that generated by abiotic reduction. Here, we show that uranium isotope fractionation discriminates readily between biotic and abiotic reduction reactions through the major environmentally relevant pathways and propose the ²³⁸U/²³⁵U isotope ratio as a new bio-proxy for ancient and modern environments.     

贫铀长期植入对大鼠肾脏损伤效应的研究

目的研究贫铀植入后不同时相点对大鼠肾脏的损伤效应。方法采用初成年健康雄性Wistar大鼠分别植入贫铀片,观察大鼠接触贫铀后3、6、12、18月其肾脏超微结构和病理形态学改变,肾功能检测和胶原染色,并采用免疫荧光和蛋白印记杂交检测肾脏不同时间段纤维化相关因子TGF—β1与Smad表达。结果植入贫铀后不同时间段大鼠肾脏出现不同程度的病理改变,表现为肾小球固缩、后继肾小管萎缩和局部肾间质纤维组织增生以及炎性细胞浸润。纤维化程度随接触时间延长而加重。胶原染色显示胶原分布主要位于肾小管周围,且具有区域性。TGF—β1与Smad是肾脏组织纤维化进程中重要的细胞因子。Western Blot分析显示贫铀接触后大鼠肾脏中TGF—β1与Smad均有不同程度的增加。结论贫铀长时间植入后大鼠肾脏可出现病理学及超微结构的改变,TGF—β1与Smad参予了其纤维化进程。     

Pedothem carbonates reveal anomalous North American atmospheric circulation 70,000–55,000 years ago

Our understanding of climatic conditions, and therefore forcing factors, in North America during the past two glacial cycles is limited in part by the scarcity of long, well-dated, continuous paleoclimate records. Here, we present the first, to our knowledge, continuous, millennial-resolution paleoclimate proxy record derived from millimeter-thick pedogenic carbonate clast coatings (pedothems), which are widely distributed in semiarid to arid regions worldwide. Our new multiisotope pedothem record from the Wind River Basin in Wyoming confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and U-Th dating by laser ablation inductively coupled plasma mass spectrometry. This pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the North American interior by westerly winds before and after 70,000–55,000 years ago, may have resulted from a persistent anticyclone developed above the North American ice sheet during Marine Isotope Stage 4. We conclude that pedothems, when analyzed using microanalytical techniques, can provide high-resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available. When pedothem paleoclimate records are combined with existing records they will add complimentary soil-based perspectives on paleoclimate conditions.During the last two glacial–interglacial cycles, North America experienced some of its most variable and dramatic changes in climate during recent Earth history. These climates were not only temporally dynamic but also, spatially nonuniform (1, 2) in ways that are not yet completely clear. In part, this lack of clarity is because the most informative records—those that are long, continuous, and dated with millennial or better resolution—have been derived primarily from speleothems and/or lake sediments that are absent or rare in large regions of the continent.In contrast, soil carbonate is nearly ubiquitous in arid and semiarid climates, and pedothems (from Greek: πέδoν, pedon, “soil”; and θέμα, théma, “deposit”), consisting of dense laminated pedogenic carbonate clast coatings, are common in these regions (SI Appendix, Fig. S1). After they are formed, pedothems are geochemically closed and retain intact U-Th systematics as evidenced by coherent monotonic age progressions spanning tens of thousands of years (SI Appendix, Figs. S2–S4). Stable isotopes of O and C, strongly bound in the carbonate group, also retain their original isotopic compositions and can provide continuous records of paleoclimate conditions for soils that have persisted through millennia of subaerial exposure (3, 4).Here, we show that micrometer-scale variations in O, C, and U isotopic ratios in carbonate pedothems preserve a continuous, datable record of environmental conditions for the last 120 ka (thousand years) in soils of the Wind River Basin (WR) of northwestern Wyoming. This record was accessed by applying laser ablation U-series dating and ion microprobe C and O stable isotope analyses. Developing this approach and applying it to midcontinent North America allow us to examine a nearly continuous record of the hydroclimates of the most recent glacial cycles in central North America, a region where records of such duration are otherwise unavailable. These data are then compared with other continental records and atmospheric circulation simulations (2, 5–9) to provide deeper insight into the spatial and temporal variabilities in North American paleoclimate.A midcontinent North American climate record is of particular interest, because previous work (3) has hinted that, during Marine Isotope Stage 4 (MIS 4; 71–57 ka) (10), atmospheric circulation over North America shifted from a state dominated by easterly flow of Pacific Ocean-sourced moisture to one dominated by northerly flow of Gulf of Mexico-sourced moisture into the continental interior. If correct, such a shift in atmospheric circulation should produce an identifiable signal in the O isotope composition of precipitation and the productivity of regional flora that are recorded in the O and C isotopic compositions of pedogenic carbonate as we show below.     

Myth: Group B streptococcal infection in pregnancy: comprehended and conquered

Group B streptococcus (GBS) is a common inhabitant of the bowel, and frequently colonises the vagina. It rarely causes disease, except in neonates, where it is the most common cause of serious neonatal infection. Although GBS can be transmitted sexually, it is common even in adults who have never been sexually active and is not a sexually transmitted disease. Currently, the most widely used effective method for detecting colonisation is taking a low vaginal and rectal swab and culturing GBS using enriched media culture. GBS cannot reliably be eradicated by antibiotic treatment but intravenous penicillin given to the mother during labour can prevent up to 90% of early onset GBS disease. Screening and antibiotic prophylaxis has resulted in an 80% fall in early onset disease in the USA, and has been successfully implemented in many countries. There is no systematic screening in the UK, where the incidence continues to rise.     

贫铀对人肾小管上皮细胞的恶性转化及苯乙酸、亚硒酸钠的抑制作用

目的:探讨贫铀(DU)是否会引起人肾小管上皮细胞(HKC)向恶性表型转化,以及抑制物是否可有效地抑制这种恶性转化. 方法: 将HKC用可溶性DU溶液(0.063～0.500 g/L)作用24 h后,再与1.0～2.5 μmol/L的苯乙酸(PA)或亚硒酸钠(SS)孵育1 d～3 mo,观察不同代龄细胞的集落形成率、生长曲线、刀豆蛋白(ConA)凝集实验、半固体琼脂集落形成率及裸小鼠成瘤性;检测脆性组氨酸三联体(FHIT)蛋白在转化细胞中的表达. 结果: 传约20～30代后,HKC在半固体琼脂中形成集落,注入裸小鼠后成瘤. 部分转化细胞的FHIT蛋白表达也较正常HKC减弱. PA, SS可明显减少HKC在半固体琼脂集落形成率至(0.6±0.1)‰,裸小鼠也无皮下肿瘤形成(0/3)(P<0.05). 结论: DU可诱发HKC向恶性表型转化;用PA,SS抑制这种恶性转化的效果相似.     

贫铀对人肾小管上皮细胞的毒性作用

目的　阐明贫铀 (depleteduranium ,DU)对人肾小管上皮细胞 (humankidneycell,HKC)的急性毒性作用及损伤部位 ,为救治提供依据。方法　将 0 0 63～ 0 5 0 0mg ml的DU溶液作用于HKC ,研究细胞超微结构、存活率的变化 ,多种酶含量的改变及HGPRT基因突变的频率。结果　 0 0 63～ 0 5 0 0mg ml浓度的DU可引起HKC细胞结构改变 ,存活率显著下降 ;溶酶体酶NAG含量随DU浓度的增加而增加 ;其他酶含量也发生变化 ;HGPRT基因突变的发生率显著高于正常对照组 ,并呈二项式相关关系。加入苯乙酸、亚硒酸钠使上述指标变化不大。结论　DU可引起细胞活力降低 ,损伤细胞膜、线粒体、溶酶体等 ,使细胞抗氧化能力下降 ;HGPRT基因突变率与DU浓度之间呈相关关系 ;加入恶性转化的抑制剂亚硒酸钠和苯乙酸 ,不会显著增加DU的毒性作用     

丰富环境对脓毒症相关性脑病小鼠认知功能的影响及NPAS4/BDNF相关机制

目的观察丰富环境对脓毒症相关性脑病小鼠认知功能的影响,并探讨神经元PAS结构域蛋白4(NPAS4)/脑源性神经营养因子(BDNF)的相关机制。方法成年雄性C57BL/6小鼠60只随机分为三组:假手术+标准环境组(SS组,n=12)、盲肠结扎穿孔(CLP)+标准环境组(CS组,n=24)和CLP+丰富环境组(CE组,n=24)。术毕三组分别饲养在标准环境和丰富环境中29d,术后29d行条件性恐惧实验,并采用免疫印迹法、高尔基染色分别检测NPAS4、BDNF及海马树突棘密度的改变。结果与SS组比较,CS组的场景性僵直时间、树突棘密度、NPAS4、BDNF水平明显降低(P0.05);与CS组比较,CE组场景性僵直时间、树突棘密度、NPAS4、BDNF水平明显升高(P0.05)。三组条件性僵直时间差异无统计学意义。结论丰富环境可明显改善脓毒症相关性脑病小鼠的认知功能损伤,这可能与其上调海马NPAS4/BDNF表达,增强海马突触可塑性有关。