Molecular ecological interaction of bacterial endophytes with their host Vitis vinifera (L)

Abstract

Bacterial endophytes live asymptomatically within plants. Plant protection properties of endophytes have drawn the attention of agricultural research and industry, resulting in their development as potential biotechnologies for better crop management. Such capabilities are the result of complex ecological interactions that endophytes engage in. Thus, understanding the interplay between bacterial endophytes and co-inhabiting organisms may provide means of exploiting such capacities. Study of endophytic bacteria has classically employed functional enzymatic assays. Recently, sequencing of genomes and metagenomics aided by metabolomics studies has provided better insights into the molecular ecology of endophytes. Evidence shows that the microbiota can have a strong influence on host fitness. Because endophytes harbor many beneficial properties and interact with many insect vectors, the question arises whether they can be used as probiotics. This is relevant because in “suppressive soils” the existence of beneficial microbiota can prevent the development of plant disease. Thus, the aim of this thesis was to study the beneficial properties of endophytic bacteria isolated from grapevine and evaluate genome structure to identify similarities with and differences between other symbionts. Also, experiments were performed to understand if the grapevine associated insect Scaphoideus titanus vectors bacterial endophytic communities between plants. Finally, the effect of endophytic colonization on plant secondary metabolism was assessed. Enzymatic assays showed that most of more than 100 endophytes isolated from grapevine benefit plant growth and health. Genome sequencing revealed both characteristic chromosome organization and gene functions that may be important for symbiosis. Also, similarities between endophytic and non-endophytic bacteria at the genome level suggested a role of ecological constraints in defining the lifestyle of these symbionts, raising awareness of the virulence potential that endophytes hold in their genomes. Through 454 sequencing, the role of S. titanus as vector was confirmed, implying that plant and insect hosts have an effect on bacterial endophytic community structure. Finally, , a possible “metabolic signature” exerted by endophytes colonizing grapevine plants was detected and the ecological implications of this signature on the symbiosis were outlined.