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></div

Expression level of genes related to phasins in <i>Herbaspirillum seropedicae</i>.

a<p>the gene identification is the same as deposited in the Genbank (accession number CP002039.1).</p><p>The expression value corresponds to the average of RPKM of two biological replicates. RPKM is defined as RPKM = total gene reads per mapped reads (millions) × gene length (kb).</p

Electrophoretic pattern of PHB granule-associated proteins from <i>Herbaspirillum seropedicae</i> SmR1 and Δ<i>phaP1</i> strains in 10% SDS-PAGE.

<p>Lanes: MW – molecular weight markers; lane 1: granule-associated proteins after granule purification from the wild type strain SmR1; lane 2: granule-associated proteins after granule purification from the Δ<i>phaP1</i> mutant strain. Phasins are indicated on the right. PhaP1was identified in lane 1 whereas PhaP2 and Hsero_2402 were identified in lane 2. Proteins were Coomassie blue R-250 stained.</p