The regulatory mechanism for PHB biosynthesis in B. thuringiensis and diverse Bacillus species is still poorly understood. We now report that disruption of the sigH gene or the gene encoding the master sporulation transcription factor Spo0A severely impaired PHB accumulation in B. thuringiensis. Complementation
of the spo0A mutation with the spo0A gene restored PHB accumulation. We have found that the requirement of Spo0A for PHB accumulation is independent of the transition state regulator AbrB and of loss of sporulation ability. We also show that Spo0A is required for the expression of three genes involved in PHB biosynthesis. These findings have uncovered a new role of Spo0A in the regulation of stationary-phase-associated cellular events. Poly(3-hydroxybutyrate) (PHB) is a polyester accumulated by numerous bacteria as an intracellular carbon and energy storage Selleckchem GDC-0068 material in response to nutritional stress (for recent reviews, see Waltermann & Steinbuchel, 2005; Jendrossek, 2009). A cluster of five PHB-related genes, that is phaP (encoding a phasin protein),
phaQ (a repressor of phaP expression), phaR (a subunit of PHB synthase), phaB (acetoacetyl-CoA reductase), and phaC (a subunit of PHB synthase), was previously identified and characterized from the PHB-producing Bacillus megaterium (McCool & Cannon, 1999; Lee et al., 2004). The PHB synthase of B. megaterium requires both the AP24534 clinical trial PhaR subunit and the PhaC subunit for activity (McCool & Cannon, 2001). The genetic organization of Bacillus thuringiensis counterparts of these five PHB-related genes is the same as that of B. megaterium. However, the regulatory mechanism for PHB biosynthesis
in diverse Bacillus species is poorly understood. The master transcription factor Spo0A is a response regulator that plays a central role in the initiation of sporulation of Bacillus subtilis and other Bacillus species (for recent reviews, see Piggot Adenosine & Hilbert, 2004; Stephenson & Lewis, 2005). Bacillus subtilis Spo0A is also known to be involved in controlling other cellular events, such as biofilm formation (Hamon & Lazazzera, 2001), development of competence for DNA uptake (Hahn et al., 1995), cannibalism (Gonzalez-Pastor et al., 2003), cold and heat resistance (Mendez et al., 2004), bacilysin biosynthesis (Karatas et al., 2003), and extracellular-degradative enzyme production (Kodama et al., 2007). Phosphorylated Spo0A is capable of binding to a specific DNA sequence, called the 0A box (5′-TGNCGAA-3′), found in promoter regions of its target genes to repress or stimulate transcription (Molle et al., 2003). The pathway to Spo0A phosphorylation involves a multicomponent phosphorelay, in which the phosphate group is initially transferred from multiple sensor histidine kinases to Spo0F, then to Spo0B, and eventually to Spo0A.