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Scales of bacterial interactions on the leaf surface

dc.contributor.advisorWiegand, Kerstin Prof. Dr.
dc.contributor.authorEsser, Daniel Sebastian
dc.titleScales of bacterial interactions on the leaf surfacede
dc.contributor.refereeWiegand, Kerstin Prof. Dr.
dc.description.abstractengMicrobial organisms are ubiquitous to habitats on Earth and they are important components in cycling of matter. This is true for the micro-scale and at global scale, and all spatial scales in between. In soils, aquatic environments, in the atmosphere, as well as inside and on higher organisms, they are highly active in the activation and recycling of organic and mineral nutrients. They regulate population dynamics as pathogens or increase host fitness by reducing the effects of pathogens and toxic compounds. Despite their high abundance in nature and their important role for the environment, little is known about the spatial distribution and interactions of microbes, especially at the micrometer scale. In my dissertation “Scales of bacterial interactions on the leaf surface”, I studied the spatial distribution of leaf-colonizing bacteria. My study system consisted of artificial single- and two-species communities of two common leaf-colonizing bacteria, Pantoea agglomerans and Pseudomonas syringae, colonizing bean leaves (Phaseolus vulgaris). At the center of my studies were fluorescence microscopic records which allowed the full measurement of the location of individual bacteria on the leaf. Additional phase-contrast micrographs revealed the location of leaf structural elements that were reported before to influence the spatial distribution of bacteria. These structural elements were glandular and hooked trichomes, leaf veins, stomata, and the network of crevices between epidermal cells (“grooves”). The resulting data set of bacterial and leaf structural point patterns were then analyzed using modern spatial statistical methods and here the pair correlation function (PCF) in particular. I analyzed the intraspecific and interspecific aggregation of both bacterial species as well as the spatial correlations between the bacterial colonizers and the leaf structural elements (Chapter 4). The correlations found by the PCF were generally interpreted to be bacterial interactions with their leaf environment. Additionally, the PCFs allowed an estimation of the spatial scale at which these interactions operate. The experiments were furthermore doubled on artificial biomimetic leaf surfaces made from PDMS (Polydimethylsiloxane) by micro molding techniques (Chapter 4). This allowed to study how much of the observed bacterial distribution patterns on leaves can be explained by leaf topography and which interactions require additional leaf physiological processes. The third main component of the dissertation involved the development of the line-to- point-pair correlation function (LPPCF). The LPPCF extends the concepts of the existing bivariate PCF to interactions between point- and line-like objects such as bacteria and the grooves between epidermal cells (Chapter 6). I present four different LPPCFs that differ in the definition of the distance between a point and a line. The dissertation makes multiple important contributions, both methodologically and with respect to the biology of leaf-colonizing bacteria. The ten most important contributions comprise the fields of microbial ecology, spatial ecology and spatial statistics. Methodology 1. Introduction of PCFs in single-cell microbiology on plant leaves (Chapter 4). 2. Introduction of a new method involving artificial biomimetic leaves for differentiating leaf topographical and leaf physiological effects on the spatial distribution of bacteria on leaves (Chapter 5). 3. Introduction of a new extension of the pair correlation function for studying spatial correlations between point- and line-like objects (Chapter 6). The new line-to-point pair correlation function reignites an overdue discussion about how linear structures affect point-like objects in ecology (Chapter 6). 4. New definitions for the distance between a point and a line are introduced. The potential-based of these distance measure may be of particular interest to many research problems in ecology (Chapter 6). 5. Line patterns can be analyzed with satisfactory precision by approximating them by nodes (if forming a network) or by random points distributed on lines (Chapter 6). Biology of leaf-colonizing bacteria 6. Bacterial individuals interact with their environment in different ways and the underlying processes operate at different spatial scales (Chapter 4). 7. The aggregation of bacteria near grooves near epidermal leaf cells is mainly driven by leaf topography (Chapters 4 and 5). 8. This aggregation near grooves operates at short distances (<15 μm; Chapter 4 & 5) 9. The aggregation of bacteria near trichomes and veins as well as the scarcity of bacteria near stomata cannot solely be explained by leaf topography (Chapter 4 & 5). 10. The effects of leaf trichomes, veins and stomata can operate also at larger scales (100 μm and more; Chapter 4).de
dc.contributor.coRefereeSchlather, Martin Prof. Dr.
dc.subject.engspatial microbial ecology, line-to-point pair correlation function, Pantoea agglomerans, Pseudomonas syringae, Phaseolus vulgarisde
dc.affiliation.instituteFakultät für Agrarwissenschaftende
dc.subject.gokfullLand- und Forstwirtschaft (PPN621302791)de

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