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DTSTAMP:20260826T174918Z
UID:1788253200@ist.ac.at
DTSTART:20260901T110000
DTEND:20260901T120000
DESCRIPTION:Speaker: Stepan Ovchinnikov\nhosted by Johannes Fink\nAbstract:
  Bacterial adaptation depends not only on the selective environment but al
 so on the genetic background that determines which variants can arise and 
 how they affect fitness. This thesis investigates how genetic background a
 ffects bacterial adaptive capacity by experimentally examining the effect 
 of insertion sequence (IS) elements activity and establishing a strain sys
 tem for future experiments to reveal the role of natural competence.The ma
 in experimental study compared Escherichia coli MG1655 with a derivative l
 acking all 45 chromosomal IS elements\, together with additional strains d
 esigned to separate the effects of IS removal from restoration of the IS-d
 isrupted gene wbbL. Replicate populations were adapted to increasing conce
 ntrations of a five-antibiotic mixture and to each antibiotic individually
 \, and their adaptive responses and evolutionary routes were compared. Und
 er mixture selection\, IS-containing and IS-free populations reached simil
 ar endpoint resistance and acquired similar numbers of mutations\, althoug
 h their mutation spectra differed significantly. IS-driven mutations were 
 rare\, indicating that IS activity contributed little to adaptation under 
 this condition. Adaptation to individual antibiotics produced larger treat
 ment-specific resistance gains and more recurrent mutations in the same lo
 ci across independently evolved populations than adaptation to the antibio
 tic mixture. The contribution of IS-driven mutations varied among antibiot
 ics and was highest under tetracycline selection. Under tetracycline treat
 ment\, IS-containing populations adapted faster and reached higher selecti
 on concentrations than IS-free populations. Inactivation of wbbL partially
  restored the adaptive capacity of the IS-free strain but did not fully el
 iminate the difference\, while IS-containing populations repeatedly access
 ed IS-mediated mutations unavailable to the IS-free strains.Earlier experi
 ments examining adaptation to ethanol\, sodium chloride\, and butanol did 
 not provide reliable evidence for differences between the IS backgrounds. 
 Growth observed at high sodium chloride and butanol concentrations during 
 selection was not retained after stress-free recovery\, whereas turbidosta
 t-based ethanol experiments revealed technical limitations of using the de
 vice for parallel long-term evolution. These results motivated the more ro
 bust antibiotic-selection design. Finally\, an experimental framework was 
 developed to test whether natural competence contributes to the adaptive c
 apacity of Bacillus subtilis. As a first step toward the proposed experime
 nts\, a genotypically verified ΔcomEC strain and characterized fluorescen
 t strains were constructed\, but the evolution experiments remain to be in
 itiated.Together\, these results show that IS elements can expand the repe
 rtoire of accessible mutations without conferring a universal adaptive adv
 antage. Whether IS activity improves adaptation depends on the selective e
 nvironment\, the wider genetic background\, and whether IS-mediated mutati
 ons provide particularly beneficial adaptive routes.
LOCATION:Central Bldg / O1 / Ballroom (I01.O1.006) and Zoom\, ISTA
ORGANIZER:
SUMMARY:Stepan Ovchinnikov: Thesis Defense: The Role of Genetic Background 
 in Bacterial Adaptation
URL:https://talks-calendar.ista.ac.at/events/6601
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