Title Page
Abstract
Contents
List of abbreviation 13
1. Introduction 14
2. Literature Review 19
2.1. The role of microbes in soil from a microbium perspective 19
2.2. What is PGPR? 20
2.3. Advancing agriculture with PGPR 22
2.4. Strain selection by mutational breeding 24
2.5. Verifying mutations 26
3. Material and Methods 29
3.1. Growth conditions of bacteria 29
3.2. In vitro plant growth promotion 29
3.3. Plant growth promotion in greenhouse conditions 30
3.4. Antagonism assay 32
3.5. Variant calling 32
4. Results 35
4.1. UV-C mutation induction 35
4.2. Enhancing tobacco growth and development in vitro 37
4.3. Plant growth promotion in greenhouse conditions 41
4.4. Fungal replacement culture 53
4.5. Variant calling 55
5. Discussion 68
6. Conclusion 72
References 73
Summary in Korean 84
Table. 1. N. tabacum cv. Xanthi shoot fresh biomass by bacterial VOCs. 40
Table. 2. Fresh weight of L. sativa var. longifolia when cultures were subirrigated with PGPR 200X dilution. 43
Table. 3. Sweet potato growth survey 51
Table. 4. B. subtilis JS-1 variants 62
Table. 5. B. subtilis JS-3 variants 63
Fig. 1. Variant calling pipeline 34
Fig. 2. Viable cells at 10-second intervals when B. subtilis JS was irradiated with UV-C 36
Fig. 3. Growth promotion of N. tabacum cv. xanthi by VOCs. 38
Fig. 4. N. tabacum cv. Xanthi aboveground biomass induced by bacterial VOCs. 39
Fig. 5. Growth promotion of Lactuca sativa var. longifolia when cultures were sub-surface irrigated with PGPR 200x dilution (day 20) 42
Fig. 6. Sweet potato (Tongchaeroo) at 7 days after planting and at 21 days after inoculation with fungus at 1 week intervals.. 45
Fig. 7. Sweet potato growth survey. 50
Fig. 8. Antifungal effect of each treatment on fungal hyphae growth 54
Fig. 9. Activation of AcuC by deacetylation of AcsA and production of the TCA cycle precursor acetyl-CoA 60
Fig. 10. Pathway blockade and acetate production by sucC gene knockout in TCA cycle 61
Fig. 11. Colony-forming ability. 65
Fig. 12. ClustalW sequence alignment of B. subtilis JS ctaE and B. subtilis JS-3 ctaE 66
Fig. 13. ClustalW sequence alignment of B. subtilis JS acuC and B. subtilis JS-3 acuC 66
Fig. 14. ClustalW sequence alignment of B. subtilis JS dhbF and B. subtilis JS-3 dhbF 67
Fig. 15. ClustalW sequence alignment of B. subtilis JS degA and B. subtilis JS-3 degA. 67