Unraveling the ecological impact of a bacterial biocontrol agent applied to melon plants: insights into phenotypic, biochemical, and microbiota changes affected by Frateuria defendens

The increasing use of bacterial biocontrol agents in agriculture raises concerns about their potential impact not only on the environment of infected plants but also on that of healthy plants. This study investigated the effects of introducing the endophytic bacterium Frateuria defendens, a potential biocontrol agent against phytoplasma diseases, on melon (Cucumis melo) as a model plant. Different isolates of F. defendens were screened for their in vitro and in planta antimicrobial activity, as well as their ability to colonize and influence the plant microbiome. Only one isolate, designated KT11, successfully colonized the melon shoot and was found in the plant sap. The antimicrobial activity of this isolate was retained in the plant sap and was confirmed in a biological test on Spiroplasma melliferum. The presence of KT11 in the plant tissue induced distinct shifts in the overall structure and diversity of the endophytic microbial populations. These significant findings emphasize the need for a comprehensive understanding of the ecological implications of introducing exogenous microbes into plant systems. This study contributes to the growing body of knowledge on the intricate interactions between plants, their microbiomes, and introduced biocontrol agents, towards performing sustainable agricultural practices.