School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

Summary 1 Summary The use of naturally occurring microbial antagonists to suppress plant diseases offers a favorable alternative to classical methods of plant protection. The soybean epiphyte, Pseudomonas syringae pv. syringae strain 22d/93 (Pss22d), exhibits a strong potential to control P. syringae pv. glycinea 1a/96 (Psg1a), the causal agent of bacterial blight of soybean. Antagonism of Pss22d against Psg1a has been proven under greenhouse and field conditions but the underlying mechanism(s) remained unknown. In frame of this work it was attempted to elucidate the influence of siderophore production on biocontrol. It was verified that Pss22d and Psg1a both produce the typical pyoverdin-type siderophore of P. syringae pathovars. In addition, the presence of a second siderophore in Pss22d was demonstrated. A first characterization of this novel achromobactin-like iron uptake system is presented. The distribution of this second siderophore among different pathovars of P. syringae was investigated. It could be shown that many but not all do produce it. Interestingly, Psg1a also belongs to the strains tested positive for this siderophore. In consequence, pathogen Psg and antagonist Pss22d produced the same set of siderophores. Thus, a direct role of competition for iron in the examined biocontrol system became unlikely. Comparison of the siderophore production in vitro showed some interesting differences in the regulation of siderophore biosynthesis between Pss22d and Psg1a. Finally, the impact of the two siderophores of Pss22d on in planta performance of respective siderophore mutants was investigated. As expected, the Pss22d siderophore mutants suppressed the pathogen in a similar manner as the wild type. Different application techniques were compared for an assessment of the impact of siderophores on epiphytical fitness of Pss22d. While no differences in survival and growth of Pss22d wt and its respective mutants were observed when wound inoculation technique was used, the siderophore mutants performed slightly poorer than the wild type when spray inoculation was applied. The phenotypes were quite variable and a potential interference by alternative iron-uptake systems need to be considered. This study presents novel information on siderophore production of plantassociated bacteria as well as on the role of iron supply for epiphytic fitness and biological control in the phyllosphere. Therefore, it can provide important information for the development of new biocontrol strategies targeting foliar plant diseases. Our results confirm the complexity of biological control systems and the need for more general information on the interaction between epiphytic microbes and plant-pathogen systems. 1
Introduction 2 Introduction Like humans and animals, plants are affected by a broad range of pathogenic microorganisms. Despite expensive pest control measure, infectious plant diseases significantly interfere with crop production. It is estimated that they diminish the attainable overall production by approximately 14% while another 6-12% of the actual harvest are lost due to post-harvest diseases (Agrios, 2005). These losses differ between crop varieties and climatic regions, but in general their percentage is higher in developing countries as compared to the industrialized world (Oerke et al., 1994). Worldwide, approximately 35 billion US Dollars are spent on chemicals for plant protection per year (Agrios, 2005). The high losses (equaling a value of more than 220 billion US Dollar) in spite of this expenses have various reasons. Increased worldwide trading and traveling brings about a fast distribution of foreign pathogens to new regions. For example, the fire blight pathogen E. amylovora was supposed to be indigenous to North America, but it has been spreading all over Europe by now (Eastgate, 2000). Monocultures grown over large areas favor epidemical spread of pathogens, while the continued use of pesticides and fungicides to suppress such outbreaks promotes the occurrence of resistant pathogens (Baker et al., 1997; McManus et al., 2002). Resistance traits from plant pathogenic bacteria can be transmitted to human pathogens, so the use of antibiotics in agriculture is largely restricted (McManus et al., 2002; Teuber, 1999). Many other agrichemicals have been proven to cause environmental damage, and consequently have been prohibited. Growing public concern on side effects of pesticides led to a revision of European commission directive 91/414/CEE regulating safety requirements and accreditation of plant protection products. The alteration of this directive in 2002 resulted in the direct withdrawal of 320 substances from the European market while at the same time the legal status of another 150 products became questionable (European Commission press release, 2002). As these 470 products equal 60% of all plant protection products previously available, the need for alternatives becomes most obvious. 2
Page 1 and 2: Siderophore production of Pseudomon
Page 3 and 4: Acknowledgements This project was s
Page 5 and 6: Abbreviations Ach achromobactin-lik
Page 7 and 8: Contents 4.1.2 Pseudomonas syringae
Page 9: Contents 5.3 Influence of sideropho
Page 13 and 14: Introduction In contrast to the rhi
Page 15 and 16: Introduction 2.1.2 Host, pathogen a
Page 17 and 18: Introduction The relationship betwe
Page 19 and 20: Introduction developement of resist
Page 21 and 22: Introduction Fe 2+ + H 2 O 2 → Fe
Page 23 and 24: Introduction 1997a; May et al., 199
Page 25 and 26: Introduction Pss22d demonstrated a
Page 27 and 28: Introduction 2.4 Aim of this study
Page 29 and 30: Material and Methods Tab. 4. Antibi
Page 31 and 32: Material and Methods Iron-free 5b m
Page 33 and 34: Material and Methods Solution3, car
Page 35 and 36: 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 and 88:
Discussion 6.2 Possible regulation
Page 89 and 90:
Discussion stationary phase transit
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,
show all

School of Engineering and Science - Jacobs University

Create successful ePaper yourself

Delete template?

Save as template?