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Discussion (acr) (cbrA-D) Fig. 26. Model of transmembrane signalling for regulation of the ferric citrate uptake . The FecA protein is the initial component in the signaling cascade, which starts at the cell surface. Binding of ferric citrate to FecA induces a conformation such that FecA interacts with FecR, which in turn converts FecI into an active sigma factor that directs RNA polymerase to the P fec promoter and initiates transcription of the fecABCDE transport genes. When iron supply is sufficient, the Fe 2+ -loaded Fur repressor inhibits transcription of the regulatory genes fecIR and of the fecABCDE transport genes. P fur the promoters to which the Fe 2+ -loaded Fur repressor binds. aa, amino acids encoded. The brackets indicate homologues from the achromobactin-like siderophore uptake system. Modified after Braun and Killman, 1999 79
Discussion stationary phase transition (Galperin, 2006; Romling & Amikam, 2006). It is possible that this signaling pathway is involved in the differentiated regulation of siderophore biosynthesis in Pss22d. The obvious differences in siderophore production observed during growth of Psg1a and Pss22d in vitro can not directly be associated to the wellinvestigated iron-mediated regulation of siderophore biosynthesis like the Fur signaling. Although iron availability did not differ between the two growth curve experiments depicted in Fig.22, the oxygen saturation of the culture medium must have varied between the two settings. Possible oxygen stress is the most likely explanation for the reduced growth of Pss22d shown in Fig.22B. It is interesting to note that Pss22d reacts to this stress by an up-regulation of synthesis of the achromobactin-like siderophore. Achromobactin is supposed to protect D. chrysanthemi against oxidative stress (Expert, 1999). It could be possible that a similar protection mechanism occurs in Pss22d. However, the pathogenic Psg1a demonstrated an opposite regulation pattern. Pyoverdin production was up-regulated under high oxygen conditions. However, while the growth rate of Pss22d was reduced under high oxygen conditions, Psg1a growth was not effected. This result could indicate that in Psg1a other means are effective to avoid oxygen stress like for example in increased production of superoxid dismutase. Up to now there is no experimental prove for this assumption. 6.3 Influence of siderophore production on epiphytic fitness of Pss22d We could clearly rule out the hypothesis, that siderophore production directly influences biological control of Psg1a by Pss22d via competition for iron. However, it was also essential to investigate the influence of siderophore production on the overall epiphytic fitness of the antagonist in planta. One of the most basic requirements for a versatile biological control agent is its ability to survive in the respective habitat. It can only suppress pathogen development sufficiently if it is able to compete with other epiphytic microorganisms. The 80
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Siderophore production of Pseudomon
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Acknowledgements This project was s
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Abbreviations Ach achromobactin-lik
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Contents 4.1.2 Pseudomonas syringae
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Contents 5.3 Influence of sideropho
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Introduction 2 Introduction Like hu
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Introduction In contrast to the rhi
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Introduction 2.1.2 Host, pathogen a
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Introduction The relationship betwe
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Introduction developement of resist
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Introduction Fe 2+ + H 2 O 2 → Fe
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Introduction 1997a; May et al., 199
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Introduction Pss22d demonstrated a
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Introduction 2.4 Aim of this study
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Material and Methods Tab. 4. Antibi
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Material and Methods Iron-free 5b m
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Material and Methods Solution3, car
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Material and Methods 3.6 Plasmids T
Page 37 and 38: Material and Methods PCR-Screening
Page 39 and 40: Material and Methods on ice for 10
Page 41 and 42: Material and Methods stained in eth
Page 43 and 44: Material and Methods 4.2.5.3 Conver
Page 45 and 46: Material and Methods 4.2.5.9 Ligati
Page 47 and 48: Material and Methods strains were s
Page 49 and 50: Material and Methods 9.5). For sign
Page 51 and 52: Material and Methods gentle shaking
Page 53 and 54: Material and Methods columns were w
Page 55 and 56: Results 5 Results 5.1 Analysis of s
Page 57 and 58: Results The 13-kb open reading fram
Page 59 and 60: Results If integration is due to a
Page 61 and 62: Results Yersiniabactin is a siderop
Page 63 and 64: Results Next, a large number of tra
Page 65 and 66: Results Nevertheless the site of tr
Page 67 and 68: Results Achr2_KpnI_rev binding site
Page 69 and 70: Results Interestingly the mutant Ps
Page 71 and 72: Results XAD4-purification yielded i
Page 73 and 74: Results After changing the mobile p
Page 75 and 76: Results P P A Fig. 21. Isoelectic f
Page 77 and 78: Results reduced in comparison to th
Page 79 and 80: Results A-E represents single inocu
Page 81 and 82: Results Tab. 10. Development of pop
Page 83 and 84: Results Tab. 11. Distribution of th
Page 85 and 86: Discussion bacteria with redundande
Page 87: Discussion 6.2 Possible regulation
Page 91 and 92: Discussion and bacterium (Loper et
Page 93 and 94: Literature Bultreys, A., Gheysen, I
Page 95 and 96: Literature Galperin, M. Y. (2006).
Page 97 and 98: Literature Mazzola, M. (2002). Mech
Page 99 and 100: Literature Schubert, S., Rakin, A.,
Page 101: Literature Zou, J., Rodriguez-Zas,
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