Essential role of the plasmid<scp><i>hik31</i></scp>operon in regulating central metabolism in the dark in<i><scp>S</scp>ynechocystis</i>sp.<scp>PCC</scp>6803

<jats:title>Summary</jats:title><jats:p>The plasmid<jats:styled-content style="fixed-case"><jats:italic>hik31</jats:italic></jats:styled-content>operon (<jats:styled-content style="fixed-case">P</jats:styled-content>3, slr6039‐slr6041) is located on the<jats:styled-content style="fixed-case">pSYSX</jats:styled-content>plasmid in<jats:italic><jats:styled-content style="fixed-case">S</jats:styled-content>ynechocystis</jats:italic>sp.<jats:styled-content style="fixed-case">PCC</jats:styled-content>6803. A<jats:styled-content style="fixed-case">P</jats:styled-content>3 mutant (Δ<jats:styled-content style="fixed-case"><jats:italic>P3</jats:italic></jats:styled-content>) had a growth defect in the dark and a pigment defect that was worsened by the addition of glucose. The glucose defect was from incomplete metabolism of the substrate, was pH dependent, and completely overcome by the addition of bicarbonate. Addition of organic carbon and nitrogen sources partly alleviated the defects of the mutant in the dark. Electron micrographs of the mutant revealed larger cells with division defects, glycogen limitation, lack of carboxysomes, deteriorated thylakoids and accumulation of polyhydroxybutyrate and cyanophycin. A microarray experiment over two days of growth in light‐dark plus glucose revealed downregulation of several photosynthesis, amino acid biosynthesis, energy metabolism genes; and an upregulation of cell envelope and transport and binding genes in the mutant. Δ<jats:styled-content style="fixed-case"><jats:italic>P3</jats:italic></jats:styled-content>had an imbalance in carbon and nitrogen levels and many sugar catabolic and cell division genes were negatively affected after the first dark period. The mutant suffered from oxidative and osmotic stress, macronutrient limitation, and an energy deficit. Therefore, the<jats:styled-content style="fixed-case">P</jats:styled-content>3 operon is an important regulator of central metabolism and cell division in the dark.</jats:p>