Identification of Proteins Associated with Polyhydroxybutyrate Granules from <i>Herbaspirillum seropedicae</i> SmR1 - Old Partners, New Players

<div><p><i>Herbaspirillum seropedicae</i> is a diazotrophic ß-Proteobacterium found associated with important agricultural crops. This bacterium produces polyhydroxybutyrate (PHB), an aliphatic polyester, as a carbon storage and/or source of reducing equivalents. The PHB polymer is stored as intracellular insoluble granules coated mainly with proteins, some of which are directly involved in PHB synthesis, degradation and granule biogenesis. In this work, we have extracted the PHB granules from <i>H. seropedicae</i> and identified their associated-proteins by mass spectrometry. This analysis allowed us to identify the main phasin (PhaP1) coating the PHB granule as well as the PHB synthase (PhbC1) responsible for its synthesis. A <i>phbC1</i> mutant is impaired in PHB synthesis, confirming its role in <i>H. seropedicae.</i> On the other hand, a <i>phaP1</i> mutant produces PHB granules but coated mainly with the secondary phasin (PhaP2). Furthermore, some novel proteins not previously described to be involved with PHB metabolism were also identified, bringing new possibilities to PHB function in <i>H. seropedicae</i>.</p>