Figure 1. Schematic representation of the B728a genome showing the different sigma factors.

The 6.09 Mb genome of B728a encodes 15 distinct sigma factors. rpoD (Psyr_4641) is the essential housekeeping sigma factor for this bacterium belonging to the σ⁷⁰ family, while rpoN (Psyr_4147) belongs to the σ⁵⁴ type of sigma factors. The other sigma factors belong to the alternative sigma factor family and include fliA (Psyr_3437), which controls the flagellar biosynthesis genes; rpoS (Psyr_1374), the starvation phase σ factor; rpoH (Psyr_4748), the heat shock sigma factor; and 10 ECF sigma factors, which are summarized in Table 2. Five of these belong to the FecI-type of ECF sigma factors, including ecf5 (Psyr_1040), ecf7 (Psyr_1107), pvdS (Psyr_1943), acsS (Psyr_2580), and ecf6 (Psyr_4731). The five ECF sigma factors characterized in this study are identified by rectangular boxes.