Moonlighting activity of threonine synthase in cyanobacterial cell death

The cellular stress induced by excessive amino acids in cyanobacterial lineages remains unclear. Amino acid-sensitive <i>Microcystis aeruginosa</i>, which lacks a complete amino acid metabolic pathway in its genome, presents a promising opportunity for investigating this phenomenon. Threonine treatment proves to be toxic to <i>M. aeruginosa</i> cells, causing stress on translation and energy generation due to amino acid imbalance. This imbalance is evident in transcriptome, proteome, and metabolome data. The amino acid imbalance resulting from threonine uptake impairs cell envelope integrity, leading to increased permeability and decreased transpeptidase activity in cells. Understanding the cell death mechanisms of this threonine-sensitive cyanobacterium provides insights into the molecular mechanisms underlying the death of nutrient-sensitive oligotrophic bacteria under nutrient-rich conditions.