Title Page

Contents

Abstract 8

Ⅰ. INTRODUCTION 10

Ⅱ. MATERIALS AND METHODS 13

1. Bacterial strains and culture conditions 13

2. Screening of mutant library and verification of the transposon-inserted region 13

3. Construction of a complemented strain and green fluorescence protein (GFP)-tagging strains 14

4. Growth curves 15

5. Detection of AHL 15

6. Biofilm formation on abiotic and biotic surfaces 16

7. Swimming motility 17

8. PCWDEs activity 17

9. Virulence 18

10. Bacteriocin assay 19

11. Sensitivity assay 19

12. A whole transcriptomics 20

13. Statistical analysis 21

Ⅲ. RESULTS AND DISCUSSION 22

1. Selection and verification of ΔexpI from in vitro transposon screen 22

2. ExpI negatively controls the initial attachment to abiotic and biotic surfaces via EPS production 25

3. ExpI positively controls the production and secretion of PCWDEs 30

4. ExpI positively controls the pathogenicity through PCWDEs 33

5. Transcriptional profiles in the response to the QS signal during Pcc21 infection 37

5-1. Expression of genes related to carocin D 46

5-2. Expression of genes related to stress response 50

Ⅳ. CONCLUSION 53

REFERENCES 54

ABSTRACT IN KOREAN 66

Table 1. Summary of selected genes regulated by ExpI during Pcc21 infection 43

Fig. 1. Effects of ExpI on the production of AHL and growth in Pcc21. (A) Confirmation of AHL production in Pcc21 wild-type (WT), ΔexpI,... 24

Fig. 2. Effects of ExpI on biofilm formation and flagellar motility. Quantification of biofilm formation by Pcc21 WT and ΔexpI on both... 29

Fig. 3. Effects of ExpI on plant cell-wall degrading enzymes (PCWDEs). The activities of Pcc21 WT, ΔexpI, and ExpI-CP were... 32

Fig. 4. Effects of ExpI on virulence on Chinese cabbages and potato tubers. Monitoring soft rot symptoms (upper panels) and... 36

Fig. 5. Volcano plot of transcriptome of ΔexpI. Volcano plot of transcriptome of Δ expI infecting to Chinese cabbage slices at 4 hpi (left panel) and 6.5 hpi (right panel), compared to WT. Statistical... 40

Fig. 6. The gene ontology (GO) classification and category. (A) The gene ontology (GO) classification and number of significantly differentially expressed genes (DEGs, ratio of log₂-fold ≥ 1)... 42

Fig. 7. Effects of ExpI on the production of carocin D. Antibacterial activity of Pcc21 WT and ΔexpI were determined by measuring clear... 49

Fig. 8. Effects of ExpI on cell viability in the presence of hydrogen peroxide. Hydrogen peroxide was added in Pcc21 cultures... 52