FIGURE 1.

A schematic presentation of the regulatory circuit for the control of alternative cell fates in B. subtilis. Spo0A is positioned at the center of the regulatory circuit, controlling genes involved in both sporulation and biofilm formation. Spo0A is activated by protein phosphorylation (Spo0A~P), often through a phosphor-relay (initiated from multiple Kin kinases and mediated by Spo0F and Spo0B). Sda is a checkpoint protein that blocks the phosphor-relay from KinA to Spo0F and thus Spo0A activation during cell exponential growth. sda is activated by DnaA during exponential growth. SinR is the biofilm master repressor for the matrix genes tapA-sipW-tasA, espA-O, and bslA. SinR is counteracted by two parallel anti-repressors (SinI and SlrA) during biofilm induction (Kearns et al., 2005; Kobayashi, 2008; Chai et al., 2009). SlrR is another counteracting protein of SinR and shares strong amino acid sequence similarity with SinR (Chu et al., 2008). These two proteins constitute a self-reinforcing double-negative loop for the mutually exclusive control of matrix genes and free-living genes (Chu et al., 2008). Red, gene regulation; blue, protein–protein interaction.