A revised model for the control of fatty acid synthesis by master regulator Spo0A in Bacillus subtilis

In starving Bacillus subtilis cells, the accDA operon encoding two subunits of the essential acetyl-CoA carboxylase (ACC) has been proposed to be tightly regulated by direct binding of the master regulator Spo0A to a cis element (0A box) in the promoter region. When the 0A box is mutated, biofilm formation and sporulation have been reported to be impaired. Here, we present evidence that two 0A boxes, one previously known (0A-1) and another newly discovered (0A-2) in the accDA promoter region are positively and negatively regulated by Spo0A∼P respectively. Cells with mutated 0A boxes experience slight delays in sporulation, but eventually sporulate with high efficiency. In contrast, cells harboring a single mutated 0A-2 box are deficient for biofilm formation, while cells harboring either a mutated 0A-1 box or both mutated 0A boxes form biofilms. We further show that the essential ACC enzyme localizes on or near the cell membrane by directly observing a functional GFP fusion to one of the enzyme's subunits. Collectively, we propose a revised model in which accDA is primarily transcribed by a major σ^A -RNA polymerase, while Spo0A∼P plays an additional role in the fine-tuning of accDA expression upon starvation to support proper biofilm formation and sporulation.