In order to feed the world population in a sustainable fashion, there is an urgent need to reduce the current levels of fertilizer and pesticide inputs. Much recent research is motivated by the promise of using growth-promoting, disease-suppressive bacteria as transferable, protective agents in agriculture, with the hope of replacing, or at least reducing the use of fertilizer and pesticides. Although many bacteria have been demonstrated to have major growth promoting and protective function under laboratory conditions, this perfomance often does not translate into reliable improvements in the field. Major obstacle are thought to be the soil's physico-chemical complexity and a staggeringly complex biotic environment. However, current methods of describing bacterial association with root also crucially lack in spatial and temporal resolution. The root has to be seen as an assembly of dynamically growing, distinct micro-environments for bacteria. If we don't understand the specific characteristics of these different micro-environments, we will not be able to understand the reasons for success or failure of bacterial colonisation of roots. Therefore, we are working on describing bacterial attraction to roots and their attachment and growth on them by making extensive use fluorescent bacteria that will allow us to monitor of bacterial metabolism and tracing their movements and growth. We are initially pursuing "simple" experiments, featuring one bacterial species on a root. With this, we aim to understand the basis of attraction between bacteria and roots. In a second step, we will extend on our findings with single bacterial species, by putting them into a context of defined bacterial communities. Our work will provide critical insights into fundamental aspects of bacterial colonization that have remained unadressed, due to a lack of efforts and tools that would allow to observed bacteria root interactions at sufficiently high resolution. This will provide a basis for a more predictive design of bacterial agents for use in agriculture.
