ETD

• bacterial motility
• chemotaxis
• leaf microbiome
• microfluidics
• phyllosphere

Chemotaxis is among the most extensively studied bacterial behaviours, particularly at the physiological level. Traditionally interpreted as a foraging strategy, it has more recently been associated with ecological roles beyond foraging across diverse environments, including oceans, soils, plants, and the human gut. In plants specifically, chemotaxis has been shown to play a significant role in pathogen entry and infection efficiency, both in the rhizosphere (the zone surrounding plant roots) and the phyllosphere (the aerial parts of plants, dominated by leaves). Among commensal bacteria, host location via chemotaxis has been identified as a pivotal step in the initiation of beneficial symbioses. Despite the influence of the phyllosphere on key ecological phenomena such as nutrient cycling and on plant health, comprehensive understanding of the prevalence and functional role of chemotaxis among leaf-associated commensals remains limited.
In this thesis, a combination of microfluidics and microscopy techniques was employed to screen a large number of environmental phyllosphere isolates for their chemotactic abilities, substrate preferences, and usage of chemotaxis in planta.
The results presented here indicate that chemotaxis represents an ecologically relevant behaviour in the phyllosphere, with roles in coping with nutrient limitation and vitamin auxotrophy, as well as in mediating spatial interactions with beneficial partners in the community.