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Streptomyces sporulation - Genes and regulators involved in bacterial cell differentiation

Larsson, Jessica LU (2010)
Abstract (Swedish)
Popular Abstract in Swedish

Det finns många skäl till varför streptomyceter är en intressant grupp av bakterier att undersöka. Den här avhandlingen fokuserar på celldifferentieringen hos dessa organismer och deras förmåga att bilda en specialiserad typ av tåliga celler som kallas sporer. Genom att studera sporuleringsprocessen hos dessa bakterier kan man lära sig mycket om fundamentala livsprocesser som celldelning, nedärvning av kromosomer, syntes av cellvägg och cellform. Kunskapen om hur dessa cellbiologiska processer är reglerade på molekylär väg i den prokaryota cellen är begränsad och det är av stor vikt att reda ut de bakomliggande mekanismerna, dels av grundvetenskapliga skäl men också för att streptomyceterna har... (More)
Popular Abstract in Swedish

Det finns många skäl till varför streptomyceter är en intressant grupp av bakterier att undersöka. Den här avhandlingen fokuserar på celldifferentieringen hos dessa organismer och deras förmåga att bilda en specialiserad typ av tåliga celler som kallas sporer. Genom att studera sporuleringsprocessen hos dessa bakterier kan man lära sig mycket om fundamentala livsprocesser som celldelning, nedärvning av kromosomer, syntes av cellvägg och cellform. Kunskapen om hur dessa cellbiologiska processer är reglerade på molekylär väg i den prokaryota cellen är begränsad och det är av stor vikt att reda ut de bakomliggande mekanismerna, dels av grundvetenskapliga skäl men också för att streptomyceterna har en stor betydelse inom områden som medicin och industri. Tillsammans producerar de en mängd olika antibiotika och används i läkemedelsindustrin för att producera dessa i stor skala. Kunskaper om biologin hos dessa bakterier och hur de reglerar tillväxt och celldelning kan vara till stor nytta för att framställa stammar lämpliga att odla i storskaliga kulturer och som ger ett högt utbyte av antibiotikum. Ett annat skäl att klargöra hur Streptomyces reglerar fundamentala livsprocesser är behovet av antimikrobiella läkemedel mot närbesläktade bakterier som Mycobacterium tuberculosis, bakterien som orsakar tuberkulos. Att förstå molekylära mekanismer bakom processer i bakteriecellen medför att läkemedel som blockerar livsviktiga funktioner kan utvecklas för att bekämpa dessa farliga patogener.

Min avhandling har klargjort några centrala delar av celldifferentieringsprocessen hos streptomyceter. Sporuleringen innebär att långa trådlika celler omvandlas till en kedja av runda sporer, och omfattas av förändringar i celldelning, kromosomdistribution och i tillväxten av cellvägg som i sin tur leder till en förändrad cellform. Syftet med denna avhandling var att hitta gener och mekanismer som reglerar dessa biologiska processer i bakteriecellen. Tidigare var bara att fåtal gener kända som krävs för sporbildning, där ibland ett antal regulatoriska proteiner.

Streptomyces coelicolor har använts som modellorganism för att undersöka funktionen av en tidigare känd regulator, WhiH, som krävs för celldelning under sporuleringen. Jag har fastställt att WhiH fungerar som en transkriptionsfaktor och kan binda till DNA. WhiH binder till ett specifikt ställe i sin egen promoter och påverkar dess aktivitet på ett ännu okänt sätt. Genen som kodar för WhiH är specifikt aktiv i de celler som omvandlas till sporer vilket styrker rollen som sporuleringregulator.

Nya gener har identifierats som tidigare inte var kända för att påverka sporulering i S. coelicolor. Karakterisering av några av dessa visar att de har intressanta funktioner som påverkar spormognad, kromosomstruktur och celldelning.

En ny modellorganism för actinomyceter, S. venezuelae har använts i ett avslutande projekt. Denna organism har några egenskaper som gör den mycket lämplig för storskaliga metoder som t.ex. transkriptionsanalys med DNA mikroarrayer. Med hjälp av detta system har gener som regleras av WhiH hittats. Fortsatta undersökningar av deras funktion och reglering kommer att ge spännande och viktiga insikter i streptomyceters cell och utvecklingsbiologi. (Less)
Abstract
Streptomycetes are Gram-positive bacteria with a complex developmental life cycle. They form spores on specialized cells called aerial hyphae, and this sporulation involves alterations in growth, morphogenesis and cell cycle processes like cell division and chromosome segregation. Understanding the developmental mechanisms that streptomycetes have evolved for regulating for example cell division is of general interest in bacterial cell biology. It can also be valuable in the design of new drugs against bacterial pathogens. Very few sporulation genes have been found with an impact on cell cycle-related processes. Finding of such genes is important for a clarification of the molecular mechanisms that are underlying the developmental control... (More)
Streptomycetes are Gram-positive bacteria with a complex developmental life cycle. They form spores on specialized cells called aerial hyphae, and this sporulation involves alterations in growth, morphogenesis and cell cycle processes like cell division and chromosome segregation. Understanding the developmental mechanisms that streptomycetes have evolved for regulating for example cell division is of general interest in bacterial cell biology. It can also be valuable in the design of new drugs against bacterial pathogens. Very few sporulation genes have been found with an impact on cell cycle-related processes. Finding of such genes is important for a clarification of the molecular mechanisms that are underlying the developmental control of fundamental cellular processes in Streptomyces. The work of this thesis has led to the identification of genes previously unknown to be developmentally regulated in Streptomyces. By comparing the transcriptome of the wildtype S. coelicolor strain M145 to two developmental mutants, whiA and whiH, which specifically affect sporulation processes, it was possible to identify differentially expressed genes. Genes that so far have been characterized proved to have important roles during sporulation, affecting spore maturation, chromosome condensation and cell division. WhiH is a central regulator in the early sporulation process and required for the developmentally controlled form of cell division in S. coelicolor. In this thesis the role of WhiH as a transcription factor has been established and WhiH was found to bind to a specific site in its own promoter and function as an autoregulator. A whiHp-mCherry reporter fusion was used to monitor cell type-specific activity of the whiH promoter in aerial hyphae, and showed that it is active before delimitation of the sporogenic cell in which multiple developmentally controlled cell divisions will be triggered. A new Streptomyces model organism, S. venezuelae, was finally exploited to identify target genes for control by WhiH. This organism sporulates efficiently in liquid culture and is well suited for global transcriptomic approaches. In this study, microarray analysis of whiH-dependent gene expression was used to find putative targets for WhiH. Combined with chromatin-immunoprecipitation (ChIP-chip) and protein-DNA binding assays this identified a group of genes that are directly repressed by WhiH during a late stage of sporulation, and also some candidate genes that could be activated by WhiH at an earlier stage. Future analyses should shed light on the functions of these genes and their potential roles in developmental and cell cycle-related processes. (Less)
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author
supervisor
opponent
  • Prof. Dr. Zakrzewska-Czerwinska, Jolanta, University of Wroclaw, Faculty of Biotechnology, Department of Molecular Microbiology
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Streptomyces coelicolor, venezuelae, morphological differentiation, WhiH, WhiA
publisher
Department of Biology, Lund University
defense location
Lecture hall, Biology building A
defense date
2010-12-09 10:00
ISBN
978-91-7473-019-7
language
English
LU publication?
yes
id
d63cfb6a-39b0-4c0f-8f9b-8699d996224e (old id 1716280)
date added to LUP
2010-11-15 13:25:40
date last changed
2016-09-19 08:45:09
@phdthesis{d63cfb6a-39b0-4c0f-8f9b-8699d996224e,
  abstract     = {Streptomycetes are Gram-positive bacteria with a complex developmental life cycle. They form spores on specialized cells called aerial hyphae, and this sporulation involves alterations in growth, morphogenesis and cell cycle processes like cell division and chromosome segregation. Understanding the developmental mechanisms that streptomycetes have evolved for regulating for example cell division is of general interest in bacterial cell biology. It can also be valuable in the design of new drugs against bacterial pathogens. Very few sporulation genes have been found with an impact on cell cycle-related processes. Finding of such genes is important for a clarification of the molecular mechanisms that are underlying the developmental control of fundamental cellular processes in Streptomyces. The work of this thesis has led to the identification of genes previously unknown to be developmentally regulated in Streptomyces. By comparing the transcriptome of the wildtype S. coelicolor strain M145 to two developmental mutants, whiA and whiH, which specifically affect sporulation processes, it was possible to identify differentially expressed genes. Genes that so far have been characterized proved to have important roles during sporulation, affecting spore maturation, chromosome condensation and cell division. WhiH is a central regulator in the early sporulation process and required for the developmentally controlled form of cell division in S. coelicolor. In this thesis the role of WhiH as a transcription factor has been established and WhiH was found to bind to a specific site in its own promoter and function as an autoregulator. A whiHp-mCherry reporter fusion was used to monitor cell type-specific activity of the whiH promoter in aerial hyphae, and showed that it is active before delimitation of the sporogenic cell in which multiple developmentally controlled cell divisions will be triggered. A new Streptomyces model organism, S. venezuelae, was finally exploited to identify target genes for control by WhiH. This organism sporulates efficiently in liquid culture and is well suited for global transcriptomic approaches. In this study, microarray analysis of whiH-dependent gene expression was used to find putative targets for WhiH. Combined with chromatin-immunoprecipitation (ChIP-chip) and protein-DNA binding assays this identified a group of genes that are directly repressed by WhiH during a late stage of sporulation, and also some candidate genes that could be activated by WhiH at an earlier stage. Future analyses should shed light on the functions of these genes and their potential roles in developmental and cell cycle-related processes.},
  author       = {Larsson, Jessica},
  isbn         = {978-91-7473-019-7},
  keyword      = {Streptomyces coelicolor,venezuelae,morphological differentiation,WhiH,WhiA},
  language     = {eng},
  publisher    = {Department of Biology, Lund University},
  school       = {Lund University},
  title        = {Streptomyces sporulation - Genes and regulators involved in bacterial cell differentiation},
  year         = {2010},
}