Abstract

Pseudomonas extremaustralis produces mainly polyhydroxybutyrate (PHB), a short chain length polyhydroxyalkanoate (sclPHA) infrequently found in Pseudomonas species. PHB genes are located in a genomic island indicating that they were acquired by horizontal transfer events. In this work, genome analysis revealed the presence of another PHB cluster, phbFPX, and a cluster phaC1ZC2D coding for medium chain length PHA production (mclPHA). All mclPHA genes showed high similarity with genes from Pseudomonas species. Although P. extremaustralis produces small amounts of mclPHA, complementation analysis showed the functionality of both mclPHA synthases, PhaC1 and PhaC2. RT-qPCR analysis showed that the PHB synthase, phbC, and the two mclPHA synthases (phaC1 and phaC2) are expressed at different levels. Expression of phbC, was significantly higher than those obtained for phaC1 and phaC2, in late exponential phase cultures. Analysis of PHA granule bound proteins 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 were detected. The results show the high efficiency of a foreign gene (phbC) in comparison with the mclPHA core genome genes (phaC1 and phaC2) and explain the ability of P. extremaustralis to produce high amounts of PHB. The study of the genes involved in PHA metabolism could be useful for biotechnological purposes in order to achieve the production of different PHAs (scl and mclPHAs) with varied elastomeric properties in the same microorganism. Genetic manipulations and optimization of culture conditions could allow the production of both kinds of PHAs in this bacterium.