Review Article

Alginate Biosynthesis in Azotobacter vinelandii: Overview of Molecular Mechanisms in Connection with the Oxygen Availability

Figure 6

Schematic representation of the possible gene regulation mechanism by oxygen in Azotobacter vinelandii. Oxygen availability is depicted in the figure as low O2 (left side) and high O2 (right side). Light red dotted boxes indicate the Na+-translocating NADH:ubiquinone oxidoreductase (Na+NQR) that regulates negatively algD and algC gene targets, although the exact mechanism of algD and algC gene regulation at high O2 by Na+NQR is still unknown. Gray slashed boxes represent the ArcB/A two-component redox sensor: under high oxygen availability, the autophosphorylation of ArcB (B blocks) is inhibited by oxidized quinones (Q8). ArcA (A blocks) in the nonphosphorylated state is unable to bind specifically to algD, alg8, and alg44 gene targets. Low oxygen causes a decrease in the level of oxidized quinones (Q8H2), allowing the autophosphorylation of ArcA. ArcA-P binds specifically to its target sites and coordinates the cellular response to oxygen availability. Arrows indicate positive regulation and T-shaped bars indicate negative regulation. Flag-type boxes indicate genes described in the figure. Question mark indicates unknown gene regulation mechanism. OM: outer membrane; PG: peptidoglycan; IM: inner membrane.