1,721,132 research outputs found
Computational modelling of pattern formation by myxobacteria
No full textMyxobacteria are social bacteria that are remarkable for their complex life cycle. In vegetative state, when nutrients are available, myxobacteria cooperatively swarm on a solid surface and feed. When exposed to starvation conditions, myxobacteria exhibit multicellular morphogenesis: 10^5-10^6 cells aggregate to form a fruiting body. Due to their unique life cycle, myxobacteria often serve as relatively simple model organism to study multicellular development and morphogenesis. Myxobacteria cells glide on a substratum, periodically reversing direction and interact with surrounding cells of a swarm. During developmental process, myxobacteria cells often form various patterns: clusters of cells, domains of aligned cells, circular aggregates and streams of cells traveling into the aggregates. The goal of the thesis was to formulate a computationally efficient mechanical mass-spring model of a myxobacterium cell and study the importance of mechanical interactions between cells for the pattern formation in myxobacteria populations. In Chapter 2, a basic model was formulated and it was investigated how cell flexibility affects cell alignment in the population in two-dimensions. The model was formulated in terms of experimentally measurable mechanical parameters, such as engine force, bending stiffness, and drag coefficient. It was shown, that a population of rigid cells can align well due to mechanical interactions between cells, but that cell flexibility impedes the alignment. Theoretical estimations of cell flexibility suggest that myxobacteria cells could be too flexible for the population to align due to mechanical interactions. Therefore, in Chapter 3 lateral restriction of cell movement due to contact with the substratum was introduced in the model. It was shown that lateral restriction can increase the ability of a population of flexible cells to align. In Chapter 4 it was studied how reversal period of cells affects population movement patterns. The results indicate that short reversal period results in domains of aligned cells, whereas long reversal period produces cell clusters. Furthermore, the model reveals that in densely packed populations, non-reversing cells can sort themselves due to mechanical interactions to produce streams of cells that travel in the same direction. Chapter 5 introduces short-range guidance forces between the trailing pole of one myxobacterium and the leading pole of another and investigates the resulting patterns. It is shown that certain types of short-range guiding interactions can explain the formation of circular aggregates. In Chapter 6, the model is extended to three-dimensions and simulation outcome is compared with the results obtained in the previous chapters. The three-dimensional model shows that guiding interactions as in Chapter 5 can initiate the formation of unstable mounds. Finally, the thesis Outlook discusses a series of directions in which the current model can be extended to further understand the importance of mechanical interactions between gliding cells on the development of myxobacteria.BiotechnologyApplied Science
Irregular biofilms are predictable: Dental plaque and other bacterial yobs, if you must eat sweets, do it quickly
No full textMicroorganisms will eventually settle on anything,living or dead. Its a simple fact of life. In most cases there is no problem, the microbes are simply part of the greater ecosystem, but in others, bacteria on and in the human body become a nuisance, sometimes with disastrous consequences. Examples include dental plaque, as well as marine and pipeline fouling. Although details of these so-called biofilms have been known for some time, the overall picture was still missing. Together with Prof. Dr. Ir. Mark van Loosdrecht, Dr. Ir. Cristian Picioreanu of the Kluyver Laboratory for Biothechnology at Delft University has developed a set of mathematical models that can paint a pretty accurate picture of what goes on inside biofilms, and he has done so without even entering the field of advanced biology! If you must eat sweets, do it quickly, is one of the conclusions from his model calculations
Don't build your whole career on a single success; interview
No full textIn the future, we will flush our toilets with seawater and the sewage system will become a source of raw materials. This is according to Spinoza prizewinner and water purification expert Professor Mark van Loosdrecht.Delft University of Technolog
Selecting for a high lipid accumulating microalgae culture by dual growth limitation in a continuous bioreactor
No full text: A dual-growth-limited continuous operated bioreactor (chemostat) was used to enhance lipid accumulation in an enrichment culture of microalgae. The light intensity and nitrogen concentration where both limiting factors resulting in high lipid accumulation in the mixed culture. Both conditions of light and nitrogen excess and deficiency were tested. Strategies to selectively enrich for a phototrophic lipid-storing community, based on the use of different nitrogen sources (ammonium vs. nitrate) and vitamin B supplementation in the growth medium, were evaluated. The dual limitation of both nitrogen and light enhanced the accumulation of storage compounds. Ammoniacal nitrogen was the preferred nitrogen source. Vitamin B supplementation led to a doubling of the lipid productivity. The availability of vitamins played a key role in selecting an efficient lipid-storing community, primarily consisting of Trebouxiophyceae (with an 82 % relative abundance among eukaryotic microorganisms). The obtained lipid volumetric productivity (387 mg L-1 d-1) was among the highest reported in literature for microalgae bioreactors. Lipid production by the microalgae enrichment surpassed the efficiencies reported for continuous microalgae pure cultures, highlighting the benefits of mixed-culture photo-biotechnologies for fuels and food ingredients in the circular economy
Greenhouse Gas Emissions from Membrane Bioreactors
Full text linkNowadays, it is widely accepted that wastewater treatment plants (WWTPs) are significant sources of greenhouse gas (GHG) emission, contributing to the anthropogenic sources. Among the GHG emitted from WWTPs, nitrous oxide (N2O) has been identified of having the major interest/concern, since its high global warming potential (GWP), is 298 times higher than that of CO2 and also to its capability to react with stratospheric ozone causing the layer depletion. Up to now, most of the experimental investigations have been carried out on conventional activated sludge (CAS) processes. The knowledge of N2O emission from advanced technologies such membrane bioreactors (MBRs) is still very limited. The present paper is aimed at providing a picture of the GHG emissions from MBR systems. In particular, data of N2O acquired from pilot plant systems monitoring are here presented. The key aim of the study was to highlight the effect of wastewater features and operational conditions on N2O production/emission from MBRs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Nitrous oxide emission in a University of Cape Town membrane bioreactor: The effect of carbon to nitrogen ratio
No full textThe effect of the carbon-to-nitrogen (C/N) ratio in the influent on the nitrous oxide (N2O) emission from a University of Cape Town Membrane BioReactor pilot plant was investigated. The membrane was located in a separate tank to single out the production of N2O due to the biological processes from N2O stripping as a result of the extra aeration needed for the mitigation of membrane fouling. The experimental campaign was divided into two phases, each characterized by a different C/N ratio (namely, 10 and 5 mgCOD/mgTN, Phase I and Phase II, respectively). The decrease of the C/N ratio promoted the increase of N2O emissions in both gaseous and dissolved phases, mainly due to a decreased nitrification/denitrification capacity of the system. The highest N2O concentration in the dissolved phase was found in the permeate. This result suggests that the dissolved N2O in the permeate stream discharged from a MBR cannot be neglected. The total N2O emission was approximately of 0.01% and 0.1% of the total influent nitrogen load for the Phase I and Phase II, respectively. The findings suggest that the C/N ratio represents an indirect cause of N2O emission; the low C/N value (Phase II) led to the increase of pH and free ammonia causing a stress effect on the growth of nitrifying species increasing the N2O emission
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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