Endohyphal bacteria are a group of bacteria that live inside the hyphae (filamentous structures) of fungi. These bacteria form a symbiotic relationship with the fungi, where they benefit from the nutrients provided by the fungi, and in turn, they assist the fungi in various ways such as nutrient uptake, defense against pathogens, and enhancing their growth and fitness. Research in endohyphal bacteria focuses on understanding the mechanisms underlying this symbiotic relationship, the diversity and distribution of these bacteria in different fungal species and ecosystems, and their potential applications in agriculture, biotechnology, and environmental remediation. Studies have shown that endohyphal bacteria play a crucial role in fungal ecology and have the potential to improve the health and productivity of plants by influencing their interactions with fungi.