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Proquest Dissertations INFORMATION TO USERS This manuscript has been reproduced from the microfihn master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zeeb Road, Ann Arbor MI 48106-1346 USA 313/761-4700 800/521-0600 STARVATION-INDUCED CHANGES IN MOTILITY AND SPONTANEOUS SWITCHING TO FASTER SWARMING BEHAVIOR OF SINORHIZOBIUM MELILOTI DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School at The Ohio State University By Xueming Wei. B.S., M.S. Department of Plant Biology The Ohio State University 1999 Dissertation Committee; Approved by Dr. W. Dietz Bauer, advisor Advisor Dr. David L Coplin Dr. Richard T. Sayre, advisor Advisor Dr. Olli H. Tuovinen Graduate Program in Plant Biology UMI Number: 9931697 UMI Microform 9931697 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 ABSTRACT Changes in motility and chemotaxis in responses to nutrient limitation have been studied in Sinorhizobium meliloti. Cells lost motility in a strain- specific pattern within 8 h to 4 d after transfer to starvation buffer. A transient, 2- to 6-fold increase in chemotactic responsiveness toward attractants was observed. Nonmetabolizable chemoattractants could prevent motility loss and partially restore the motility of starving cells. Thus, interactions of chemoreceptors with attractants appear to affect motility independently of nutrient availability. Most nonmotile cells retained flagella, indicating that deactivation of flagellar motors was the first important response of S. meliloti to nutrient deprivation. Several Tn5 mutants of S. meliloti which swarmed twice as faster as the parent in semi-solid agar, moist sand and viscous liquid were identified. The faster swarming (FS) mutants outgrew the wild type 30- to 40-fold within 2 d in soft agar plates and had a significant growth advantage in all circumstances where nutrient gradients were present. The mutants had higher percentages of motile and flagellated cells, and longer and more flagella than the wild type. Thus FS behavior is likely a result of derepression of flagellar synthesis. Spontaneous variants that behaved exactly like the Tn5 FS mutants ii were obtained at a frequency of about 1 per 15,000 cells. These FS variants reverted to wild-type behavior at low, but variable frequencies. The FS mutants and variants produced less exopolysaccharide (EPS) than the wild type. Various swarm rates, swim patterns, EPS phenotypes, and restriction patterns observed in different FS mutants indicate that multiple genetic configurations could result in FS behavior. The significant competitive advantage of the FS mutants over the wild type suggests that behavioral switching may be an important adaptation in natural habitats. Preliminary molecular characterization have shown that the Tn5 insertion sites in five of the six FS mutants were all in the same location within about 50 bp. The sequences flanking the Tn5 did not complement the mutant behavior, nor did marker exchange of the Tn5 into the parent recreate the FS phenotype. Complementing sequences have been isolated and are being characterized. Possible molecular mechanisms for FS-EPS phenotype and for switching are discussed, and future directions presented. In many Gram-negative bacteria, expression of certain genes is regulated by N-acyl-derivatives of homoserine lactone (AHL). We investigated the effect of mutations in AHL production and reception on growth and plant root colonization by Pseudomonas aeruginosa. Mutants defective in either AHL synthesis or signal perception were found to grow more slowly than the wild type in both moist sand and on roots. Our results indicate that AHL signalling plays a significant role in growth at low cell densities, in root colonization and in the development of a stress resistant subpopulation. iii ACKNOWLEDGMENTS Million of thanks goes to my advisor. Dr. W. D. Bauer, for his guidance, patience, encouragement, and support, especially when the project encountered difficulties. I am greatly grateful to my advisory committee members, Drs. David L. Coplin. Richard T. Sayre, Olli H. Tuovinen. Fred Sack, and Ralph E. J. Boerner for their constructive ideas, advice on the project and beyond, and for their willingness to be my future references. The assistance of Catherine Wolkin, Elke Kretschmar and Robert Whitmoyer with electron microscope is greatly appreciated. I wish to thank Drs. Dave Coplin. John Leigh and Graham Walker for providing strains and plasmids, and Drs. Jyan-Chyun Jang, Jayne Robinson. Ms. Doris R. Majerczak and Ms. Debbie Estes for technical helps. Ohio Agricultural Research and Development Center, and OSU Graduate School Alumni Research Award provided partial support for salaries and experimental supplies. Chapters 2 and 3 were already published as; Wei. X.. and W. D. Bauer. 1998. Starvation-induced changes in motility, chemotaxis and flagellation of Rhizobium meliloti. Appl. Environ. Microbiol. 6 4 : 1708- 1714.; and as: Wei. X.. and W. D. Bauer. 1999. Tn5-induced and spontaneous switching of Sinorhizobium meliloti to faster-swarming behavior. Appl. Environ. Microbiol. 65:1228-1235. This dissertation is dedicated to all my family members who have been supporting me with all their hearts and soul throughout all the ups and downs for these long years. IV VITA 1981: B. S. degree; major: microbiology, minor: soil science and agrochemistry. Nanjing Agricultural University, Nanjing, and Department of Biology, Northwestern University, Xi'an, P. R. China. 1984: M. S. degree; major: soil and agricultural microbiology. Nanjing Agricultural University, P. R. China. 1985—1990: Lecturer, Laboratory of Agricultural Microbiology, Nanjing Agricultural University, P. R. China. PUBLICATIONS 1. Wei, X., and W. D. Bauer. 1998. Starvation-induced changes in motility, chemotaxis, and flagellation of Rhizobium meliloti. Appl. Environ. Microbiol. 64:1708-1714. 2. Wei, X., and W. D. Bauer. 1999. Tn5-Induced and spontaneous switching of Sinorhizobium meliloti to faster swarming behavior. Appl. Environ. Microbiol. 65:1228-1235. FIELD OF STUDY Major: Plant Biology Areas of research and interests: Plant-microbe interactions Microbial ecology Molecular biology TABLE OF CONTENTS ABSTRACT ............................................................................................ ii ACKNOWLEDGEMENTS..................................................................... iv CURRICULUM VITA.............................................................................. v LIST OF TABLES................................................................................... viii LIST OF FIGURES................................................................................. x LIST OF ABBREVIATIONS.................................................................. xii SCOPE OF THE STUDY ..................................................................... 1 CHAPTER PAGE 1 INTRODUCTION AND LITERATURE REVIEW ................. 3 I. Chemotactic motility as a way of response to environmental signals .............................................. 3 II. Bacterial locomotion ............................................................ 6 1. Motility of flagellated species ............... .......................... 7 2. Motility in nonflagellated bacterial species .................... 13 III. Tactic responses in bacteria ................................................ 14 1. Types of bacterial taxis .................................................... 15 2. Signal transduction in E. coli chemotaxis ...................... 17 IV. Role of motility and chemotaxis in bacterial fitne ss 21 V. S. meliloti and Its unique features regarding motility and chemotaxis ........................................................ 25 VI. Goals of this study ................................................................. 29 2 STARVATION-INDUCED CHANGES IN MOTILITY AND CHEMOTAXIS IN SINORHIZOBIUM MELILOTI .................. 31 Abstract ............................................................................................. 31 Introduction .........................................................................................
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