|dc.contributor.advisor||Wiegand, Kerstin Prof. Dr.||
|dc.contributor.author||Esser, Daniel Sebastian||
|dc.title||Scales of bacterial interactions on the leaf surface||de
|dc.contributor.referee||Wiegand, Kerstin Prof. Dr.||
|dc.description.abstracteng||Microbial 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
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.
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.coReferee||Schlather, Martin Prof. Dr.||
|dc.subject.eng||spatial microbial ecology, line-to-point pair correlation function, Pantoea agglomerans, Pseudomonas syringae, Phaseolus vulgaris||de
|dc.affiliation.institute||Fakultät für Agrarwissenschaften||de
|dc.subject.gokfull||Land- und Forstwirtschaft (PPN621302791)||de