RB-TnSeq of H. neapolitanus as a function of CO2 concentration

One approach to constructing contemporary analogues of CCM ancestors is to remove CCM genes from a native host. If CCM components were acquired sequentially, some single gene knockouts would be analogous to recent ancestors, e.g . those lacking a complete carboxysome shell. We tested this approach by assaying a whole-genome knockout library of a proteobacterial chemoautotroph, H. neapolitanus, in five CO2 partial pressures. We found that many CCM genes contribute substantially to organismal fitness even at CO2 concentrations tenfold greater than present-day atmosphere (0.5% CO2), supporting the view that CCM components play an important physiological role even in relatively high environmental CO2 concentrations.