Ecology and human pathogenicity of plant-associated bacteria

Plant species and organs are colonised by diverse bacterial communities, which fulfil important functions for their host. Plant-associated bacteria have a great potential in diverse areas of biotechnology, e.g. as biological control agents (BCAs) in plant protection. Although many of them have a positive interaction with their host plants, they can interact with other eukaryotic hosts like humans in a pathogenic way. This review presents an overview about these bacteria that have bivalent interactions with plant and human hosts. We discuss mechanisms of the interactions and their behaviour and ecology. Another important issue is to detect those potentially dangerous bacteria by reliable test systems, and to exclude them from biotechnological applications. The Caenorhabditis elegans slow killing assay is such a bioassay, which is presented and discussed with examples. Besides human health, effects on the environment, especially on structure and function of microbial communities, are discussed. Diverse studies show that BCA application resulted only in transient, short-term effects.