Anatomy of the pneumococcal nucleoid:Visualizing replication, chromosome segregation and chromosome condensation dynamics in Streptococcus pneumoniae

The pneumococcus is a bacterium that lives in the upper part of the throat behind the nose of many children and adults. In most cases it lives there harmlessly, but sometimes, it can move further into the body and cause serious illnesses as pneumonia or meningitis. Understanding how this bacterium grows could give us starting points for antibacterial drugs: if you can stop growth, you can stop the bacterium. Bacteria grow by cell division. The pneumococcus is no different: it grows in two directions, after which a wall is formed in the middle and the bacterium splits into two daughter cells. During this division cycle, the internal components of the cell need to be copied and brought to the two cell halves. In this thesis, we use several microscopy techniques to map how the DNA of the pneumococcus is copied and split into two so-called 'nucleoids' during the cell cycle. First, we benchmarked Red Fluorescent Proteins (RFPs) in the pneumococcus and developed analysis software to be able to create a map of the internal organization of the pneumococcus. Then, we followed different parts of the chromosome and proteins important for the cell cycle. We found that the correct splitting of the DNA in two nucleoids is also important for the correct placement of the septum in the middle of the cell. This shows that also in the pneumococcus, cell division and chromosome organization are connected processes

Tidal resuspension and deposition of particulate matter in the Oyster Grounds, North Sea

Moored current meters, fluorom eters and transmissometers were used in combination with sediment traps (aspect ratio \u3e4) and shipborne sampling to determine fluxes of deposition and resuspension of total suspended matter (TSM) under tidal action in the 45 m deep Oyster Grounds, North Sea. Here, we present data from the mixed layer below the major thermocline at about 20 m above the bottom (mab) as obtained during a 14-day period of calm weather in July 1994. Around neap tide near-bottom current velocities remained smaller than 0.15 m s-1 and TSM was dominated by particles advected from a relatively turbid area to the southeast of the study site. At the onset of spring tide, current speeds increased with maximum values greater than 0.20 m s-1 and seabed friction velocities exceeding the threshold value for resuspension. Particles resuspended were strongly enriched with organic carbon compared to the bulk sediment, suggesting that not the bed proper but a fine-grained fluff fraction was eroded. This resuspended fluff was by far the dominant source for the mass fluxes in the sediment trap (at 3.2 mab), which showed a distinct tidal cycle with highest fluxes directly after low water slack tide and lowest fluxes during maximum ebb current. This pattern was caused by variations in apparent settling velocity of TSM, presumably due to floc formation during periods in the tidal cycle when current speeds were low and relatively high concentrations of both chlorophyll-a and TSM were found. From a simple model on advection, deposition and resuspension of TSM, we calculated a net accumulation on the sediment of 75 g m-2 during the 14-day study period, which is the difference between gross fluxes of deposition and resuspension. Upon deposition, the average retention time of particles until their next resuspension is calculated at 1-2 weeks, which may be sufficient for substantial decomposition of organic matter associated with TSM. This implies that, upon resuspension, particles transported further along the shelf are relatively poor in organic carbon. It is concluded that the Oyster Grounds serve as a mid-shelf temporary depocenter and that mineralization in this and similar areas may play a crucial role in the carbon budget of the North Sea

Chromosome segregation drives division site selection in Streptococcus pneumoniae.

Accurate spatial and temporal positioning of the tubulin-like protein FtsZ is key for proper bacterial cell division. <i>Streptococcus pneumoniae</i> (pneumococcus) is an oval-shaped, symmetrically dividing opportunistic human pathogen lacking the canonical systems for division site control (nucleoid occlusion and the Min-system). Recently, the early division protein MapZ was identified and implicated in pneumococcal division site selection. We show that MapZ is important for proper division plane selection; thus, the question remains as to what drives pneumococcal division site selection. By mapping the cell cycle in detail, we show that directly after replication both chromosomal origin regions localize to the future cell division sites, before FtsZ. Interestingly, Z-ring formation occurs coincidently with initiation of DNA replication. Perturbing the longitudinal chromosomal organization by mutating the condensin SMC, by CRISPR/Cas9-mediated chromosome cutting, or by poisoning DNA decatenation resulted in mistiming of MapZ and FtsZ positioning and subsequent cell elongation. Together, we demonstrate an intimate relationship between DNA replication, chromosome segregation, and division site selection in the pneumococcus, providing a simple way to ensure equally sized daughter cells

Absorbed Mn2+ and Mn redox cycling in Iberian continental margin sediments (northeast Atlantic Ocean)

Although Mn2+ sorption has been investigated extensively in the laboratory, the role of Mn2+ sorption in natural marine sediments remains speculative. Our objectives were to study (1) the role of Mn2+ sorption in the redox cycling of Mn, (2) to quantify Mn cycling and (3) to identify its rate-determining factors at the Iberian margin. Profiles of pore water Mn2+, adsorbed Mn2+ and solid phase Mn were measured together with benthic oxygen fluxes along three transects across the margin from the shelf to the deep sea as well as in the Nazeré Canyon. In the profiles, peaks of adsorbed Mn2+ were observed in-between those of solid phase Mn and pore water Mn2+. We propose that upon Mn reduction, the produced Mn2+ is adsorbed onto adjacent Mn oxide or oxyhydroxide surfaces. Available adsorption-sites diminish and/or saturate as Mn reduction continues, upon which Mn2+ is released into the pore water. Mn redox chemistry is controlled by the organic carbon flux to the sediment. A simple steady state model was formulated that includes Mn2+ sorption as a combination of an instantaneous reversible equilibrium process and a first-order kinetic reaction. Model derived, depth integrated rates of Mn reduction as well as Mn2+ desorption and oxidation rates range between 1 and 35 µmoles m-2 d-1. Mn cycling is most intense at moderate carbon fluxes. Moreover, Mn cycling is enhanced at higher deposition fluxes of Mn oxide in the canyon. Budgets based on the model indicate that adsorbed Mn2+ is an important redox intermediate between Mn oxide and pore water Mn2+ in the reduced sediment layer. Adsorption of Mn2+ restrains the efflux of dissolved Mn2+ into the water column, by lowering the pore water gradient at stations with a thin oxidation zone. There, adsorbed Mn2+ enhances the retention of Mn2+ in the sediment column

Effect van CO2-dosering bij Cymbidium : effect op productie en kwaliteit en economische evaluatie

Vanwege de mogelijkheid om extra CO2 aan te kunnen kopen via de OCAP was de vraag in de praktijk in hoeverre aankoop van extra CO2 bij Cymbidium een rendabele meeropbrengst in productie en/of kwaliteit kan geven. Tot dusver wordt in de Cymbidiumteelt meestal alleen CO2 gedoseerd als er CO2 beschikbaar is van de ketel. Gedurende 2 teeltjaren is het effect vastgesteld van CO2-dosering bij Cymbidium. CO2-doseren tot 800 ppm met max. 150 kg CO2 per uur per ha gaf bij snijCymbidium een kleine verbetering van de productie (+5%) en kwaliteit. Het totaal geproduceerde versgewicht aan bloemtakken was gemiddeld 10% hoger. CO2-dosering tot 1200 ppm met max. 300 kg per uur per ha gaf bij snijCymbidium minder goede resultaten en lijkt niet zinvol. Bij potCymbidium gaf juist de hoogste CO2-dosering de beste resultaten met gemiddeld 13% meer bloemtakken dan de controlebehandeling. De extra kosten voor CO2-doseren tot 800 ppm met max. 150 kg CO2 per uur per ha zijn €0,84 per m2 per jaar en voor 1200 ppm CO2 met max. 300 kg per uur per ha €2,07 per m2 per jaar. De netto meeropbrengst als gevolg van 5% productieverhoging is berekend op € 0,27/m2 voor grootbloemige snijCymbidium en € 0,11/m2 voor kleinbloemige snijCymbidium. Dit is exclusief een mogelijke meeropbrengst als gevolg van een betere takkwaliteit