The most frequently PHA produced is poly(3-hydroxybutyrate) or PHB [2]. The ability to produce PHB has been correlated with improved survival under stress conditions or in competitive environments [5, 6]. PHB is generally produced in conditions of carbon oversupply and low levels of other nutrients such as nitrogen, phosphate or oxygen [7]. The biosynthesis of PHB is dependent on the activity of the following enzymes: (i) a 3-ketothiolase which condenses two acetyl-CoA yielding acetoacetyl-CoA (encoded by phbA), (ii) a NADPH-dependent acetoacetyl-CoA

reductase which reduces acetoacetyl-CoA to (R)-3-hydroxybutyryl-CoA selleck chemicals llc (encoded by phbB) and (iii) the PHB synthase (encoded by phbC) that catalyses the polymerization of (R)-3-hydroxybutyryl-CoA to form the polymer [8, 9]. This polymer is stored intracellularly as insoluble inclusion bodies called PHB granules [1] which also contain about 2% protein as well as phospholipids [10]. The main protein associated with the PHB granules is phasin (encoded

by phaP) which prevents coalescence of WDR5 antagonist PHB granules by coating the granule surfaces [11–14]. However, other proteins have also been found associated with the granules, including transcriptional regulators such as PhaF from Pseudomonas oleovorans GPo1, PhaR from Paracoccus denitrificans, and PhaR from Ralstonia Target Selective Inhibitor Library chemical structure eutropha H16 [15–17]. Expression of enzymes involved in PHA/PHB biosynthesis and the granule-associated phasin are reported to be regulated at the transcriptional level [15, 16, 18–26]. This regulation may include repressors as well as activators [21]. The proteins PhbR from Azotobacter vinelandii UW136 [22] and PhaD from Pseudomonas putida KT2442 [24] are transcription activators. In contrast, PhaR of P. denitrificans represses phaR expression by

binding to a TGC rich region which overlaps the -35/-10 promoter [16]. In R. eutropha H16 the PhaR protein binds to the -35/-10 phaP promoter at two sites: the transcriptional start site and upstream from the -35 at the promoter region, thereby blocking RNA polymerase [17]. The PhaR binding site determined in R. eutropha comprises two 12 bp Fossariinae repeated sequences not related to those observed in P. denitrificans, suggesting that DNA-binding sites for PhaR recognition and the mechanisms of regulation may vary. The β-Proteobacterium Herbaspirillum seropedicae SmR1 is a plant-endophytic diazotroph found in association with economically important graminaceous species such as sugar cane, sorghum, rice and maize [27]. H. seropedicae SmR1 has been already described as a PHB producer using glucose as carbon source [28], however the molecular aspects of its PHB metabolism have not been addressed. The H.