Cell morphology governs directional control in swimming bacteria

The ability to rapidly detect and track nutrient gradients is key to the ecological success of motile bacteria in aquatic systems. Consequently, bacteria have evolved a number of chemotactic strategies that consist of sequences of straight runs and reorientations. Theoretically, both phases are affected by fluid drag and Brownian motion, which are themselves governed by cell geometry. Here, we experimentally explore the effect of cell length on control of swimming direction. We subjected Escherichia coli to an antibiotic to obtain motile cells of different lengths, and characterized their swimming patterns in a homogeneous medium. As cells elongated, angles between runs became smaller, forcing a change from a run-and-tumble to a run-and-stop/reverse pattern. Our results show that changes in the motility pattern of microorganisms can be induced by simple morphological variation, and raise the possibility that changes in swimming pattern may be triggered by both morphological plasticity and selection on morphology

Structure–property relation and relevance of beam theories for microtubules: a coupled molecular and continuum mechanics study

Quasi-one-dimensional microtubules (MTs) in cells enjoy high axial rigidity but large transverse flexibility due to the inter-protofilament (PF) sliding. This study aims to explore the structure–property relation for MTs and examine the relevance of the beam theories to their unique features. A molecular structural mechanics (MSM) model was used to identify the origin of the inter-PF sliding and its role in bending and vibration of MTs. The beam models were then fitted to the MSM to reveal how they cope with the distinct mechanical responses induced by the inter-PF sliding. Clear evidence showed that the inter-PF sliding is due to the soft inter-PF bonds and leads to the length-dependent bending stiffness. The Euler beam theory is found to adequately describe MT deformation when the inter-PF sliding is largely prohibited. Nevertheless, neither shear deformation nor the nonlocal effect considered in the ‘more accurate’ beam theories can fully capture the effect of the inter-PF sliding. This reflects the distinct deformation mechanisms between an MT and its equivalent continuous body

Köln Radiocarbon Dates III

This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

A new hot-mix design method for Southern Africa

Paper presented at the South African Transport Conference 17 - 20 July 2000 "Action in transport for the new millennium", CSIR International Convention Centre, Pretoria, South Africa.This paper was transferred from the original CD ROM created for this conference. The material on the CD ROM was published using Adobe Acrobat technology. The original CD ROM was produced by Document Transformation Technologies Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected] URL: http://www.doctech.co.z

Einfluss der autochthonen Mikroflora auf die Sorption und Remobilisierung des Technetiums und des Selens an verschiedenen Sedimenten Abschlussbericht

In this research project the influence of autochthonous micro-organisms on immobilisation and remobilization of Technetium and Selenium was investigated. Both radionuclides are part of the nuclear fuel waste (Tc app. 6%). Former investigations have shown, that immobilisation behaviour of both elements can be influenced by micro-organisms. The autochthonous population of micro-organisms in deep sediments and their influence on immobilisation of Tc and Se was investigated in this study. For this reason recirculation column tests were carried out. Absolutely sterile and anaerobic handling is necessary handling the sediments and waters used for the experiments. Special methods for sampling, storage and handling were developed. More than 30 sediments have been investigated. The number of colony forming units (CFU) has always been relatively low (less than E+06 CFU). The results of recirculation column tests with autochthonous micro-organisms were compared with sterilized (Co-60) parallel tests and were verified with the results of hydrochemical equilibration code PHREEQUE. Instead of the allochthonous micro-orgamisms the autochthonous organisms showed no significant fixation of the radionuclides due to microbial activity. This is true for various temperatures of 10 C (aquifer temperature) and 20 C (normal laboratory temperature). An addition of an inoculum of the autochthonous micro-organisms developed at breeding temperature of 10 and 20 C had no influence on the radionuclide mobility. Performing conventional laboratory experiments you have to consider an overestimated retardation capacity because of an inevitable contamination with allochthonous micro-organisms. (orig.)In dem Forschungsvorhaben wurde der Einfluss der autochthonen Mikroorganismen auf das Immobilisierungsverhalten von Technetium und Selen untersucht. Beide redoxsensitiven Radionuklide sind im Abfall von Kernbrennelementen enthalten (Tc ca. 6%). Aus vorangegangenen Forschungsarbeiten ist bekannt, dass das Immobilisierungsverhalten der beiden Elemente durch Mikroorganismen beeinflusst werden kann. Nicht bekannt jedoch war, welche Mikroorganismen in Sedimenten aus groesseren Teufen vorkommen und welchen Einfluss diese auf das Immobilisierungsverhalten zeigen. In dieser Studie wurden ca. 30 Grundwasserleitermaterialien auf ihre autochthonen Mikroorganismen (MO) untersucht. Die Zahl der Koloniebildenden Einheiten (KBE) war immer relativ gering (weniger als E+06 KBE). Die Ergebnisse aus Umlaufsaeulenversuchen mit autochthonen MO wurden verglichen mit Proben, die durch Co-60-Bestrahlung sterilisiert wurden. Es zeigte sich, dass die im Boden vorhandenen autochthonen Mikroorganismen vor allem aufgrund ihrer geringen Populationsdichte keinen signifikanten Einfluss auf die Mobilitaet zeigen. Dies bestaetigt sich auch bei einer Versuchstemperatur von 20 C (Labortemperatur) gegenueber 10 C (Grundwasserleitertemperatur) sowie nach der Zugabe eines Inokulums aus autochthonen Mikroorganismen, die jeweils bei 10 C und 20 C bebruetet wurden. Bei konventionell durchgefuehrten Laborversuchen zur Abschaetzung der Rueckhaltekapazitaeten von Sedimenten gegenueber Schadstoffen muss, wegen der unvermeidbaren mikrobiellen Kontamination, mit der Moeglichkeit zu hoher Sorptionsraten bei redoxsensitiven Elementen gerechnet werden. (orig.)Available from TIB Hannover: F99B15 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Einfluss der autochthonen Mikroflora auf die Sorption und Remobilisierung des Technetiums und des Selens Abschlussbericht

In dem Forschungsvorhaben wurde der Einfluss der autochthonen Mikroorgansimen auf die Mobilitaet von Technetium und Selen untersucht. Beide redoxsensitiven Radionuklide sind im Abfall von Kernbrennelementen enthalten (Tc ca. 6%). Aus vorangegangenen Forschungsarbeiten ist bekannt, dass die Mobilitaet der beiden Elemente durch Mikroorganismen beeinflusst werden kann. Es war jedoch nicht bekannt, welche Mikroorganismen in Sedimenten aus groesseren Tiefen vorkommen und welchen Einfluss sie auf die Mobilitaet ausueben. Fuer die Durchfuehrung von Umlaufsaeulenversuchen unter Verwendung von Sedimenten mit autochthoner mikrobieller Besiedlung ist es erforderlich bei der Probennahme und Bearbeitung auf sterile Handhabung und Konservierung der im Sediment angetroffenen physikochemische Bedingungen zu achten. Hierfuer wurden spezielle Techniken zur Probennahme, Lagerung und Verarbeitung der Proben entwickelt. Die Ergebnisse der Umlaufsaeulenversuche mit autochthoner mikrobieller Besiedlung wurden denen von parallel durchgefuehrten Sterilversuchen gegenuebergestellt und mit Hilfe einer erweiterten Version des hydrochemischen Modellierungsprogrammes PHREEQE ueberpueft. Es zeigte sich, das die im Boden vorhandene Mikroorganismen vor allem aufgrund ihrer ausserordentlich geringen Populationsdichte (von<10 E+6 KBE) nur einen sehr geringen Einfluss zeigen. Jedoch laesst sich bemerken, dass bei konventionell durchgefuehrten Laborversuchen zur Abschaetzung der Rueckhaltekapazitaeten von Sedimenten gegenueber Schadstoffen durch mikrobielle Kontamination mit zu hohen Sorptionsraten bzw. Festlegungsraten gerechnet werden muss. (orig.)Within this research project the influence of autochthonous mirco-organisms on immobilization and remobilization of Technetium and Selenium was investigated. Both redoxsensitive radionuclides are part of the waste of nuclear fuel (Tc app. 6%). Former investigations have shown, that immobilization behaviour of both elements could be influenced by micro-organisms. It has not been known, if the autochthonous (or in situ) organisms from greater depth do also have an influence on radionuclide mobility. The autochthonous populations of micro-organisms in deep sediments and their influence on the migration of Tc and Se were investigated in this study. For this reason recirculation column experiments were carried out. Absolutely sterile and anaerobic handling was necessary for the sampling and the further treatment of the sediments and waters used in the experiments. Therefor special methods for sampling, storage and handling had been developed. The results of recirculation column test with autochthonous micro-organisms were compared with sterile parallel tests and were verified with the results of an elaborated version of the hydrogeochemical equilibration code PHREEQE. It was shown that the autochthonous micro-organisms had only very little influence on the migration behaviour. The reason is the very low population (less than 10 E+6 CFU). Nevertheless it has to be taken into consideration, that conventional laboratory experiments for the estimation of the retention capacities of sediments for hazardous waste lead to an overestimation, if the sediments are contaminated with allochthonous micro-organisms (CFU=colony forming units). (orig.)Available from TIB Hannover: F97B1413 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman