Long-term Phanerozoic global mean sea level: Insights from strontium isotope variations and estimates of continental glaciation

Global mean sea level is a key component within the fields of climate and oceanographic modelling in the Anthropocene. Hence, an improved understanding of eustatic sea level in deep time aids in our understanding of Earth's paleoclimate and may help predict future climatological and sea level changes. However, long-term eustatic sea level reconstructions are hampered because of ambiguity in stratigraphic interpretations of the rock record and limitations in plate tectonic modelling. Hence the amplitude and timescales of Phanerozoic eustasy remains poorly constrained. A novel, independent method from stratigraphic or plate modelling methods, based on estimating the effect of plate tectonics (i.e., mid-ocean ridge spreading) from the 87Sr/86Sr record led to a long-term eustatic sea level curve, but did not include glacio-eustatic drivers. Here, we incorporate changes in sea level resulting from variations in seawater volume from continental glaciations at time steps of 1 Myr. Based on a recent compilation of global average paleotemperature derived from δ18O data, paleo-Köppen zones and paleogeographic reconstructions, we estimate ice distribution on land and continental shelf margins. Ice thickness is calibrated with a recent paleoclimate model for the late Cenozoic icehouse, yielding an average ∼1.4 km thickness for land ice, ultimately providing global ice volume estimates. Eustatic sea level variations associated with long-term glaciations (>1 Myr) reach up to ∼90 m, similar to, and is at times dominant in amplitude over plate tectonic-derived eustasy. We superimpose the long-term sea level effects of land ice on the plate tectonically driven sea level record. This results in a Tectono-Glacio-Eustatic (TGE) curvefor which we describe the main long-term (>50 Myr) and residual trends in detail

Multidrug and peptide export in Lactococcus lactis

Multidrug resistentie (MDR) is een fenomeen waarbij organismen een resistentie ontwikkelen tegen een breed scala van giftige verbindingen die qua (chemische) structuur niet aan elkaar verwant zijn. MDR wordt veroorzaakt door transporteiwitten die deze verbindingen op een energieafhankelijke wijze kunnen uitscheiden. De melkzuurbacterie Lactococcus lactis wordt in de industrie toegepast bij de productie van kaas en andere voedingsmiddelen. Dit micro-organisme bevat verschillende MDR transporters, te weten LmrA, LmrP en LmrCD. LmrA behoort tot een klasse transporteiwitten die verwant zijn aan het humane P-glycoproteïne dat in kankercellen resistentie tegen cytostatica kan veroorzaken. In dit proefschrift beschreven studies tonen aan dat LmrA en P-glycoproteïne mogelijk ook betrokken zijn bij resistentie tegen zware metalen. Bij het bestuderen van het werkingsmechanisme van MDR transporteiwitten wordt veelvuldig gebruik gemaakt van fluorescente verbindingen zoals ethidium bromide en Hoechst 33342, die als substraat kunnen fungeren. Echter het Hoechst 33342-transport in membraanblaasjes blijkt geen betrouwbare indicator voor MDR-afhankelijk transport. Zowel LmrA als LmrP als LmrCD vertonen deze specifieke transportactiviteit, terwijl alleen LmrCD ook daadwerkelijk resistentie verleent voor deze toxische stof. Melkzuurbacteriën kunnen zich niet alleen beschermen tegen toxische moleculen in hun omgeving, ze kunnen ook zelf de bron hiervan zijn. Het best bestudeerde, door melkzuurbacteriën geproduceerde antimicrobiële peptide is het lantibioticum nisine A. De synthese van nisine A verloopt via het NisBCT eiwitcomplex. In dit proefschrift wordt aangetoond dat NisB belangrijk is voor effectieve productie van dit lantibioticum en een centrale component vormt binnen het NisBTC eiwitcomplex, waarbij de uitscheiding van dit molecuul gekoppeld lijkt te zijn aan de biosynthese. English: Organisms can develop resistance to a broad spectrum of chemically and structurally unrelated toxic compounds, a phenomenon called multidrug resistance (MDR). MDR can be caused by transporter proteins that secrete these compounds in an energy-dependent manner. The lactic acid bacterium Lactococcus lactis is used in industry for the production of cheese and other food. This microorganism harbours several MDR transport proteins, namely LmrA, LmrP and LmrCD. LmrA belongs to a class of transport proteins related to the human P-glycoprotein that can cause resistance to chemotherapy drugs in cancer cells. Studies described in this thesis show that LmrA and P-glycoprotein may also be involved in heavy metal resistance. Research on the molecular mechanism of MDR proteins often involves fluorescent compounds such as ethidium bromide and Hoechst 33342, which serve as substrate. However, Hoechst 33342 transport in membrane vesicles proves to be an unreliable indicator of MDR transport. LmrA, LmrP, and LmrCD all exhibit this specific transport activity, while only LmrCD actually confers resistance to these toxic compounds. Lactic acid bacteria not only protect themselves against toxic compounds, they also produce their own. The best studied antimicrobial peptide produced by these bacteria is the lantibiotic nisin A. The synthesis of nisin A goes via the NisBCT protein complex. In this thesis it is shown that NisB is crucial for efficient production of this lantibiotic and forms a central component within the NisBCT complex, where secretion of nisin A appears to be coupled to the biosynthesis.

The control of climate and base-level change on the stratigraphic architecture of fluvio-deltaic systems, investigated by quantitative analogue modelling

River systems play an important role in the filling of sedimentary basins and record the history of external forcing processes, such as climate, tectonics and sea-level change, acting on them. They are potential reservoirs for oil, gas and water, and can host coal and placer mineral deposits. Because of the complex interplay between the external forcing processes, however, understanding of the genesis of the stratigraphy of river systems and interpreting the stratigraphy correctly is far from straightforward. Current conceptual models are oversimplified, and more insight into the impact of external forcing processes must be gained to improve these models. The aim of this study was to assess the impact of climate (i.e., discharge and sediment influx) on the development of the large-scale stratigraphic architecture of river systems, in isolation and in conjunction with sea-level fluctuations, through an analogue modelling approach. Analogue physical models reproduce the long-term average effects and products of the transport processes in a river system, rather than the transport processes themselves. An advantage of analogue modelling over numerical modelling is that it is hard to make the model fit preconceived notions about the results, making it possible to test and develop conceptual models. The impact of climate (i.e., discharge and sediment influx) on the large-scale stratigraphic architecture of river-delta-shelf-basin systems appears not to be as dominant as the impact of sea-level change, but it does significantly affect the smaller scale stratigraphic architecture, such as the relative size of systems tracts and the rate and extent of erosion. Furthermore, we found a fundamental difference between the impact of changes in discharge and the impact of changes in sediment influx on the yield and mass accumulation at the mouth of a river system. River systems can act as buffers for rapid changes in sediment influx, while they react very rapidly to changes in discharge. Thus, the small-scale stratigraphy at the river mouth is controlled mainly by changes in discharge, and the large-scale stratigraphy is controlled by changes in sediment influx (and sea-level fluctuations). Also, because the response of the river gradient to an increase in discharge is the opposite to its response to an increase in sediment influx (and vice versa), the mass accumulation at the river mouth, combined with the overall stratigraphic architecture of the system, can be used to constrain paleo-discharge and paleo-sediment influx scenarios. Finally, our experiments show that a complex stratigraphic architecture is not necessarily the result of complex forcing, but can result from very simple changes in discharge. To assess the development of the stratigraphy in physical models, a new method for processing the data obtained in the experiments was developed. Series of subsequent digital elevation models of the surface of the model are converted, using custom-made software, into synthetic three-dimensional stratigraphy, containing true isochronous surfaces. This data set contains the development of the system through time in three dimensions, and can be presented in various formats, such as geological maps, geological sections and Wheeler diagrams

The control of climate and base-level change on the stratigraphic architecture of fluvio-deltaic systems, investigated by quantitative analogue modelling

River systems play an important role in the filling of sedimentary basins and record the history of external forcing processes, such as climate, tectonics and sea-level change, acting on them. They are potential reservoirs for oil, gas and water, and can host coal and placer mineral deposits. Because of the complex interplay between the external forcing processes, however, understanding of the genesis of the stratigraphy of river systems and interpreting the stratigraphy correctly is far from straightforward. Current conceptual models are oversimplified, and more insight into the impact of external forcing processes must be gained to improve these models. The aim of this study was to assess the impact of climate (i.e., discharge and sediment influx) on the development of the large-scale stratigraphic architecture of river systems, in isolation and in conjunction with sea-level fluctuations, through an analogue modelling approach. Analogue physical models reproduce the long-term average effects and products of the transport processes in a river system, rather than the transport processes themselves. An advantage of analogue modelling over numerical modelling is that it is hard to make the model fit preconceived notions about the results, making it possible to test and develop conceptual models. The impact of climate (i.e., discharge and sediment influx) on the large-scale stratigraphic architecture of river-delta-shelf-basin systems appears not to be as dominant as the impact of sea-level change, but it does significantly affect the smaller scale stratigraphic architecture, such as the relative size of systems tracts and the rate and extent of erosion. Furthermore, we found a fundamental difference between the impact of changes in discharge and the impact of changes in sediment influx on the yield and mass accumulation at the mouth of a river system. River systems can act as buffers for rapid changes in sediment influx, while they react very rapidly to changes in discharge. Thus, the small-scale stratigraphy at the river mouth is controlled mainly by changes in discharge, and the large-scale stratigraphy is controlled by changes in sediment influx (and sea-level fluctuations). Also, because the response of the river gradient to an increase in discharge is the opposite to its response to an increase in sediment influx (and vice versa), the mass accumulation at the river mouth, combined with the overall stratigraphic architecture of the system, can be used to constrain paleo-discharge and paleo-sediment influx scenarios. Finally, our experiments show that a complex stratigraphic architecture is not necessarily the result of complex forcing, but can result from very simple changes in discharge. To assess the development of the stratigraphy in physical models, a new method for processing the data obtained in the experiments was developed. Series of subsequent digital elevation models of the surface of the model are converted, using custom-made software, into synthetic three-dimensional stratigraphy, containing true isochronous surfaces. This data set contains the development of the system through time in three dimensions, and can be presented in various formats, such as geological maps, geological sections and Wheeler diagrams