Rhizobia are a group of soil bacteria that engage in a nitrogen-fixing symbiosis with leguminous plants. Most of them belong to the class Alphaproteobacteria. This taxon is highly diverse, containing autotrophic, heterotrophic, aquatic, soil-dwelling, plant-symbiotic, and animal-symbiotic bacteria, and is distributed widely across various environments. The taxon also shares a common ancestor with mitochondria. The evolution of alphaproteobacterial diversity can be attributed to their intrinsic adaptability as well as to the lateral transfer of new genes. I am devoted to the (educational) study of key mechanisms underlying the adaptability of rhizobia (and other plant-associated alphaproteobacteria) to stressful environments. One of our research topics is the molecular mechanism of cellular protein turnover and iron-sulfur cluster biogenesis, which are crucial for successful plant infection. My main approaches involve bacterial genetic analysis via isolation of various mutants and molecular analysis using genomic information. I aim to generalize the results from this rhizobium study to understand the primary adaptive mechanism that underlies the diversity of living organisms and their lifestyles.