- σ19 (FecI) - the ferric citrate sigma factor, regulates the fec gene for iron transport.
- σ24 (RpoE) - the extracytoplasmic/extreme heat stress sigma factor.
- σ28 (RpoF) - the flagellar sigma factor.
- σ32 (RpoH) - the heat shock sigma factor, it is turned on when exposed to heat.
- σ38 (RpoS) - the starvation/stationary phase sigma factor.
- σ54 (RpoN) - the nitrogen-limitation sigma factor.