초록
<P><I>Pseudomonas extremaustralis</I> produces mainly polyhydroxybutyrate (PHB), a short chain length polyhydroxyalkanoate (sclPHA) infrequently found in <I>Pseudomonas</I> species. Previous studies with this strain demonstrated that PHB genes are located in a genomic island. In this work, the analysis of the genome of <I>P. extremaustralis</I> revealed the presence of another PHB cluster <I>phbFPX,</I> with high similarity to genes belonging to <I>Burkholderiales,</I> and also a cluster, <I>phaC1ZC2D,</I> coding for medium chain length PHA production (mclPHA). All mclPHA genes showed high similarity to genes from <I>Pseudomonas</I> species and interestingly, this cluster also showed a natural insertion of seven ORFs not related to mclPHA metabolism. Besides PHB, <I>P. extremaustralis</I> is able to produce mclPHA although in minor amounts. Complementation analysis demonstrated that both mclPHA synthases, PhaC1 and PhaC2, were functional. RT-qPCR analysis showed different levels of expression for the PHB synthase, <I>phbC</I>, and the mclPHA synthases. The expression level of <I>phbC</I>, was significantly higher than the obtained for <I>phaC1</I> and <I>phaC2</I>, in late exponential phase cultures. The analysis of the proteins bound to the PHA granules showed the presence of PhbC and PhaC1, whilst PhaC2 could not be detected. In addition, two phasin like proteins (PhbP and PhaI) associated with the production of scl and mcl PHAs, respectively, were detected. The results of this work show the high efficiency of a foreign gene (<I>phbC</I>) in comparison with the mclPHA core genome genes (<I>phaC1</I> and <I>phaC2</I>) indicating that the ability of <I>P. extremaustralis</I> to produce high amounts of PHB could be explained by the different expression levels of the genes encoding the scl and mcl PHA synthases.</P>