Isolation and Characterization of a Novel Motility Mutant in SALMONELLA TYPHIMURIUM

<p>A new mutant, BT40, isolated from mutagenized cultures of <em>S. typhimurium</em> was deficient in chemotaxis (Che^- phenotype) in tryptone semisoft agar, but had random motility with a tumbling frequency (37%) similar to that of the parental strain, ST23 (39%). In spatial assays accumulation of BT40 cells in capillary tubes containing attractants was decreased by 33%-59% compared to ST23, but BT40 had a normal response to attractants in temporal assays. The methylation level of the chemotactic proteins was decreased in BT40. At room temperature, the mean swimming speed was 11 μm/s for BT40 and 20 μm/s for ST23; more BT40 cells wobbled (50%) than ST23 cells (30%), also. The proportion of time that the flagella rotated in the clockwise direction was 5% for BT40 and 28% for ST23. Motile BT40 cells had only 1-3 flagella per cell, and the length of the flagellar filaments was only 40% of the normal. The mutant phenotype was designated as CheG^- and conjugational studies located <em>cheG</em> between 12 min and 33 min on the chromosomal map. Transductional crosses with <em>fla</em> mutants indicated that <em>cheG</em> was located in flagellar region I at 23 min, and complementation analysis with <em>recA fla</em> strains mapped <em>cheG</em> in <em>flaFVIII</em>. Transductional analysis of spontaneous revertants indicated that besides intragenic revertants, there were pseudorevertants with at least 4 types of suppressor mutations: type I suppressors, linked to the class I <em>Tn10</em> by 16%, were located between the <em>Tn10</em> and <em>cheG</em>; type II suppressors, linked to the class I <em>Tn10</em>. by 7%, were distal to <em>cheG</em> with respect to the <em>Tn10</em>; type III were linked to the class I <em>Tn10</em> by 1%; type IV suppressors were not linked to the class I <em>Tn10</em> and included in this type were the suppressor linked by over 60% to the class II <em>Tn10</em>. The CheG^- phenotype was due to a defect in a flagellar gene that caused the mutant to have short flagella and fewer flagellar filaments resulting in a decrease in the stability of the flagellar bundle. This instability accounted for occurrence of random motility in BT40 even though the individual flagella had a bias to counterclockwise rotation. It is postulated that the <em>cheG</em> mutation prevented normal expression of operons downstream to <em>flaFVIIl</em> in the flagellar regulatory cascade resulting in the pleiotropic defects observed in BT40 cells.</p>

Name thesis:degree_name

Doctor of Philosophy (Medical Science)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biochemistry

Year

1985

Author dc:creator

• Chacko, David Matthew

Contributors dc:contributor

• Barry L. Taylor
• W. Barton Rippon
• R. Bruce Wilcox
• Anthony Zuccarelli
• Jun-ichi Ryu

• Biochemistry
• Microbiology
• Salmonella typhimurium.

Statement dc:rights

• This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Language dc:language

English

Repository record dc:identifier

https://scholarsrepository.llu.edu/etd/1398

OAI identifier oai:identifier

oai:scholarsrepository.llu.edu:etd-2166