We have been working (1) on toxin-antitoxin systems in bacteria and archaea, which regulate cell growth and cell death by inhibiting various cellular essential functions such as DNA replication, mRNA stability, ATP production, and protein synthesis. These systems also play important roles in antibiotic resistance in pathogenic bacteria, and (2) the evolution of the genetic code, as to how the current 64 genetic codons have evolved since the origin of life.