Most of the carbon supplied by the plant is used to fuel nitrogen fixation,

however, under certain GSK690693 molecular weight circumstances, some of the carbon appears to be diverted by the bacteroid into the production of intracellular carbon storage polymers such as poly-3-hydroxybutyrate (PHB). This is a characteristic of bacteroids found in determinate nodules but not of PF-6463922 cell line indeterminate nodules (reviewed in [4]). Within the bacteroid, PHB deposits can be visualized as defined, electron-transparent granules located within the cytoplasm [5–7]. S. meliloti forms indeterminate nodules on the roots of its host plant alfalfa (Medicago sativa). These nodules are characterized by the existence of a persistent apical meristem and an elongated morphology. Within the nodule, the bacteroids persist and progress through defined zones of bacteroid differentiation [8]. Indeed, loss of PHB granules from the cytoplasm of the bacteria invading indeterminate nodules is a well-documented phenomenon that occurs at a specific point within bacteroid development [9].

Bacteroids of indeterminate nodules undergo such large physiological and metabolic changes relative to those of determinate nodules [10] that, until recently, it was unclear whether mature bacteroids within selleck indeterminate nodules retained the capacity to synthesize and store PHB. A recent study [11] clearly demonstrated that bacteroids of R. leguminosarum bv. viciae, which forms indeterminate nodules on pea plants, retain the capacity to synthesize and store large quantities of PHB but only when carbon supply is in excess and bacteroid metabolism is limited by the availability of a key nutrient (reviewed in [4]). During

saprophytic growth, PHB accumulation occurs during periods of nutrient deprivation when carbon is in excess. This strategy is employed by many species of bacteria. The first step in PHB degradation is catalyzed by a substrate-specific depolymerase. PHB undergoes a transition from an amorphous granule in the intracellular state to a denatured semi-crystalline form upon release into the environment. As a result, different PHB depolymerases are employed depending on the nature of the substrate. While extracellular Nintedanib (BIBF 1120) depolymerases have been identified and characterized in a wide variety of bacteria, very little is yet known about their intracellular counterparts. To date, only a handful of intracellular PHB depolymerases have been reported in the literature, most of which appear to lack the typical lipase box motif (Gly-X-Ser-X-Gly) associated with extracellular PHB depolymerases [12–17]. While the enzymes responsible for the synthesis and storage of PHB have been characterized in a wide variety of bacteria, including the rhizobia (reviewed in [4]), only a few studies have investigated the role of intracellular PHB depolymerases and, to date, no studies have reported the characterization of a rhizobial PHB depolymerase. Here we report the cloning and characterization of PhaZ from S.