Electron tunneling properties of outer-membrane decaheme cytochromes from Shewanella oneidensis

We have characterized the outer-membrane decaheme cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 at the single-molecule level using scanning tunneling microscopy (STM) and tunneling spectroscopy (TS). These cytochrome proteins are of great interest because they are thought to mediate bacterial electron transfer reactions in anoxic waters that control the reductive dissolution of oxide minerals. In our study, to characterize the electron transfer properties of these proteins on a model surface, the purified cytochromes were chemically immobilized as molecular monolayers on Au(111) substrates via a recombinant tetra-cysteine sequence as verified by X-ray photoelectron spectroscopy. Atomic force microscopy images confirm the monolayer films were ∼5-8 nm thick which is consistent with the apparent lateral dimensions of individual cytochrome molecules obtained with STM. Current-voltage TS of single cytochrome molecules revealed that OmcA and MtrC have different abilities to mediate tunneling current despite having otherwise very similar molecular and biochemical properties. These observations suggest that, based on their electron tunneling properties, the two cytochromes could have specific roles during bacterial metal reduction. Additionally, this study establishes single-molecule STM/TS as an effective means for revealing insights into biogeochemical redox processes in the environment.     

Living and working in urban working class communities

Much has been written on the apparent urban renaissance in UK cities and the new lifestyle arrangements, working time patterns, economic activities and the more general reordering of work and life that appears to accompany it. Certainly, recent decades have witnessed a range of economic, social and cultural changes in the lives of those living and working in cities and surrounding suburbs. Much of the attention in this work has focused on those groups for whom the changes have appeared most profound: the high-income earners returning to live in the city - the gentrifiers - or those who suffer multiple deprivations as a result of economic restructuring. Seemingly absent from many accounts of urban change are those places where, at first glance, the effects of change have been less pronounced: low-income, working class neighbourhoods where most people continue to get by, albeit in the context of a harsher, and less secure political economic context. In light of this apparent silence, this paper draws on interviews from Wythenshawe in South Manchester, to examine how low-income mothers cope, live and labour, in a rapidly changing city, as they perform paid work at the same time as ensuring the social reproduction of the household.     

Sea level,climate change and coastal evolution in Morar,northwest Scotland

Analyses of geomorphologically contrasting sites in Morar, NW Scotland, describe the forcing mechanisms of coastal change. Isolation basins (i.e. basins behind rock sills and now isolated from the sea following isostatic uplift) accumulated continuous marine and freshwater sediments from c.12 to 2 ka BP. Raised dune, marsh and wetland sites register breaching, migration and stability of dunes from c. 9 to 2 ka BP. High-resolution methods designed to address issues of macroscale and microscale sea-level changes and patterns of storminess include 1-mm sampling for pollen, dinocyst and diatom analyses, infra-red photography, X-ray photography and thin-section analysis. The data enhance the record of relative sea-level change for the area. Major phases of landward migration of the coast occurred during the period of low sea-level rise in the mid-Holocene as the rate of rise decreased from c. 3 to < 1 mm/year. Relative sea-level change controls the broad pattern of coastal evolution at each site; local site-specific factors contribute to short-term process change. There is no record of extreme events such as tsunami. Within a system of dynamic metastable equilibrium, the Holocene records show that site-specific factors determine the exact timing of system breakdown, e.g. dune breaching, superimposed on regional sea-level rise. The global average sea-level rise of 3 to 6 mm/yr by AD 2050 predicted by IPCC would only partly be offset in the Morar area by isostatic uplift of about 1 mm/yr. A change from relative sea-level fall to sea-level rise, in areas where the regional rate of uplift no longer offsets global processes, is a critical factor in the management of coastal resources.     

Stress fields of the San Andreas and Queen Charlotte transform faults

Analytic solutions to the stress fields resulting from the San Andreas and Queen Charlotte transform faults may be found by applying conformal mappings to the generalized plane stress solution of stresses in a half-plane. The mean stress fields (one-half the trace of the stress tensor) found in this manner show a similarity to the deformation found in western Canada and the western United States. The results refute the hypothesis that Alaska acts as a continental buttress against deformation of the Canadian Cordillera. Moreover, these results imply that the differences in the tectonics of major transform boundaries are caused primarily by differences in lithospheric structure and differences in stress distribution along the plate boundaries.     

Atmospheric Moisture Residence Times and Cycling: Implications for Rainfall Rates and Climate Change

New estimates of the moistening of the atmosphere through evaporation at the surface and of the drying through precipitation are computed. Overall, the e-folding residence time of atmospheric moisture is just over 8 days. New estimates are also made of how much moisture that precipitates out comes from horizontal transport versus local evaporation, referred to as recycling. The results depend greatly on the scale of the domain under consideration and global maps of the recycling for annual means are produced for 500 km scales for which global recycling is 9.6%, consisting of 8.9% over land and 9.9% over the oceans. Even for 1000 km scales, less than 20% of the annual precipitation typically comes from evaporation within the domain. While average overall atmospheric moisture depletion and restoration must balance, precipitation falls only a small fraction of the time. Thus precipitation rates are also examined. Over the United States, one hour intervals with 0.1 mm or more are used to show that the frequency of precipitation ranges from over 30% in the Northwest, to about 20% in the Southeast and less than 4% just east of the continental divide in winter, and from less than 2% in California to over 20% in the Southeast in summer. In midlatitudes precipitation typically falls about 10% of the time, and so rainfall rates, conditional on when rain is falling, are much larger than evaporation rates. The mismatches in the rates of rainfall versus evaporation imply that precipitating systems of all kinds feed mostly on the moisture already in the atmosphere. Over North America, much of the precipitation originates from moisture advected from the Gulf of Mexico and subtropical Atlantic or Pacific a day or so earlier. Increases in greenhouse gases in the atmosphere produce global warming through an increase in downwelling infrared radiation, and thus not only increase surface temperatures but also enhance the hydrological cycle, as much of the heating at the surface goes into evaporating surface moisture. Global temperature increases signify that the water-holding capacity of the atmosphere increases and, together with enhanced evaporation, this means that the actual atmospheric moisture should increase. It follows that naturally-occurring droughts are likely to be exacerbated by enhanced potential evapotranspiration. Further, globally there must be an increase in precipitation to balance the enhanced evaporation but the processes by which precipitation is altered locally are not well understood. Observations confirm that atmospheric moisture is increasing in many places, for example at a rate of about 5% per decade over the United States. Based on the above results, we argue that increased moisture content of the atmosphere therefore favors stronger rainfall or snowfall events, thus increasing risk of flooding, which is a pattern observed to be happening in many parts of the world. Moreover, because there is a disparity between the rates of increase of atmospheric moisture and precipitation, there are implied changes in the frequency of precipitation and/or efficiency of precipitation (related to how much moisture is left behind in a storm). However, an analysis of linear trends in the frequency of precipitation events for the United States corresponding to thresholds of 0.1 and 1 mm/h shows that the most notable statistically significant trends are for increases in the southern United States in winter and decreases in the Pacific Northwest from November through January, which may be related to changes in atmospheric circulation and storm tracks associated with El Niño–Southern Oscillation trends. It is suggested that as the physical constraints on precipitation apply only globally, more attention should be paid to rates in both observations and models as well as the frequency of occurrence.     

The present day formation of apatite in Mexican continental margin sediments

Results of pore water and sediment analyses from the western Mexican continental margin strongly suggest the present day formation of apatite. The interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments. Apatite is identified within this maximum via X-ray diffraction but is elsewhere undetectable in the core. Radioisotopic thorium, uranium, and radium data support the conclusion that this deposit is modern. The present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value.     

Middle-fan deposits from the late precambrian kongsfjord formation submarine fan,Northeast Finnmark,Northern Norway

The 3.2 km-thick late Precambrian Kongsfjord Formation Submarine Fan shows well-developed middle-fan facies-associations. Channel deposits are characterised by discrete packets of coarse-grained, medium to thick-bedded, amalgamated sandstone turbidites and other mass-flow deposits, generally 10 to 30 m thick. Individual beds, or packets of beds, wedge out and channel bases cut down by up to 11 m over a lateral distance of 150 m. Channel deposits often comprise a thinning-and-fining-upward sequence although they vary greatly in clarity. Interchannel deposits occur as packets, tens of centimetres to 25 m thick, of thin and very thin bedded Bouma T_cde siltstones and mudstones. Palaeocurrents within interchannel deposits commonly diverge from those of adjacent channel sandstones. Within the interchannel deposits, isolated beds or packets of beds occur that are both thicker bedded and coarser grained than the surrounding beds; these unusual deposits are sheet-like or fill small channels, and are interpreted as crevasse splays, lobes and channels. Packets, up to a few metres thick, of laterally discontinuous siltstone turbidites occur immediately above some of the channel sandstones, rarely below, and in some cases within interchannel deposits. These siltstones are thin to medium-bedded, show Bouma T_cd, with T_c often as climbing-ripple lamination, and commonly show soft-sediment deformation as slides, slumps, liquefaction and fluidisation structures. Palaeoflow within these packets, compared to adjacent channel sandstones, diverges by up to 90°, and in some cases channel sandstones are seen to pass laterally into these deposits with a swing in palaeocurrents from parallel to the inferred channel axis, to perpendicular to it. These deposits are thought to be levees. Channel-margin deposits are most distinctive, and they are recognised by extreme lateral wedging of channel sandstones, with concomitant thinning and fining of individual beds and their amalgamation towards the channel axis. Sliding and slumping of channel margin deposits is common. Throughout the Kongsfjord Formation Submarine Fan, channel sandstone palaeocurrents suggest a sediment-transport direction to the NE quadrant, although some channels funnelled sediment towards the southeast.