자료유형  

 학위논문

Control Number  

0016931153

International Standard Book Number  

9798380393348

Dewey Decimal Classification Number  

574.191

Main Entry-Personal Name  

Kamdar, Shashank.

Publication, Distribution, etc. (Imprint  

[S.l.] : University of Minnesota., 2022

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2022

Physical Description  

1 online resource(146 p.)

General Note  

Source: Dissertations Abstracts International, Volume: 85-03, Section: B.

General Note  

Advisor: Cheng, Xiang;Francis, Lorraine.

Dissertation Note  

Thesis (Ph.D.)--University of Minnesota, 2022.

Restrictions on Access Note  

This item must not be sold to any third party vendors.

Summary, Etc.  

요약In the 1670s, Leeuwenhoek used a single-lens microscope to bring the unfamiliar microscopic world of bacteria to human attention. In this research work, we use biophysical tools of quantitative microscopy and fluid dynamics to revisit the same world of microbes and shed light on the intricate yet fascinating motion of microbes. In particular, this thesis details two fundamentally significant problems related to microbial locomotion: 1) motility of microbes in complex fluids, and 2) impact of multiflagellarity on bacterial motility. Locomotion of flagellated microorganisms is of great importance for a wide range of biological processes from disease infection, to reproduction, and to ecosystem health. Bacterial swimming in simple Newtonian fluids is well understood; however, our understanding of their motion in their natural habitats comprising of microscopic particles and polymers is still far from complete. Even after six decades of research, whether bacteria show motility enhancement in polymer solutions and what is the origin of this enhancement remain under debate. We tackled this problem from a new perspective: we studied bacterial locomotion in dilute colloidal suspensions, which do not exhibit complex rheological behaviors such as shear thinning, thickening, etc. Surprisingly, we found that all the measurable swimming features of bacteria in colloidal suspensions are quantitatively the same as those in polymer solutions. This suggests a common origin of bacterial motility enhancement in all complex fluids and challenges all the existing theories which exclusively used polymer dynamics to explain this behavior. We subsequently developed a simple hydrodynamic model considering the colloidal nature of complex fluids, which predicted bacterial motility enhancement in both colloidal suspensions and polymer solutions. We also propose a new mechanism of bacterial wobbling that shows the enhancement and also reproduced bacterial helical trajectories with large pitches-another puzzling behavior of bacterial locomotion. Thus, our study combining experiments and theory unambiguously resolved the long-standing controversy of two problems at once, i.e., the origin of bacterial motility enhancement in complex fluids and the mechanism of bacterial wobbling in Newtonian fluids. Bacterial species also show variations in their flagellar architecture and adapt two common arrangements: monotrichous or uniflagellar bacteria possess a single flagellum at the pole of their body and peritrichous bacteria grow multiple flagella over their body, which form a helical rotating bundle propelling bacterial swimming. Although the cellular features of bacteria are under strong evolutionary selective pressures, extensive studies suggest that multiflagellarity confers no noticeable benefit to bacterial motility. These findings pose a long-standing question: why does multiflagellarity emerge in bacteria given the tremendous metabolic cost of flagellar synthesis? Here, contrary to common views that seek the answer beyond the basic function of flagella in motility, we show that multiflagellarity indeed provides a significant selective advantage in bacterial motility, allowing bacteria to maintain a constant swimming speed over a wide range of body sizes. Through experiments of immense sample sizes and detailed hydrodynamic modeling and simulations, we quantitatively reveal how bacteria utilize the increasing number of flagella to regulate the flagellar motor load, which leads to faster flagellar rotational speeds balancing the higher hydrodynamic drag on the bacterial body of larger sizes. Without such an elegant mechanism, the swimming speeds of uniflagellar bacteria decrease with increasing body sizes. This stark difference between the two swimming modes provides a novel fluid dynamic insight into the crucial role of multiflagellarity in maintaining optimum motility for navigation and survival in their native habitats. Beyond, the ecological implications, results, and insights from this thesis serve as guidelines for devising artificial swimmers that efficiently navigate complex biological environments for drug delivery.

Subject Added Entry-Topical Term  

Biophysics.

Subject Added Entry-Topical Term  

Fluid mechanics.

Subject Added Entry-Topical Term  

Microbiology.

Index Term-Uncontrolled  

Bacterial locomotion

Index Term-Uncontrolled  

Complex fluids

Index Term-Uncontrolled  

Flagella

Index Term-Uncontrolled  

Fluid mechanics

Index Term-Uncontrolled  

Microscopy

Index Term-Uncontrolled  

Motility

Added Entry-Corporate Name  

University of Minnesota Chemical Engineering

Host Item Entry  

Dissertations Abstracts International. 85-03B.

Host Item Entry  

Dissertation Abstract International

Electronic Location and Access  

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Control Number  

joongbu:640893