Abstract

Recently, the relevance of the lonA gene product from B. sacchari in the mobilization of poly-3-hydroxybutyrate (P3HB) was identified. The phaZa1 gene product from Ralstonia eutropha was also identified as the most relevant to promote P3HB mobilization in mutants of B. sacchari. In order to evaluate the roles of the products of phaZa1 and lonA genes from R. eutropha in P3HB mobilization, the recombinant E. coli strain harboring the accumulation operon (pSK::phaCAB) was engineered to express these genes in different vectors (pBBR1MCS-2::phaZa1, pBBR1MCS-5::lonA and pBBR1MCS-5::phaZa1+lonA) under P3HB mobilization culture conditions. No significant P3HB mobilization was detected when phaZa1 or lonA were expressed individually along with the genes for P3HB accumulation (phaCAB). On the other hand, when phaZa1 and lonA were co-expressed, a significant amount of the accumulated P3HB was mobilized. These results are compatible with the need of both phaZa1 and lonA to establish an effective mobilization of P3HB. However, the P3HB mobilization rates varied from 10% to 70%. This variance can be consequence of the vectors used (pBBR1MCS-2 and pBBR1MCS-5). Since both belong to the same incompatibility group, it is natural that occur a competition between them to keep themselves in the cell. When both genes were co-expressed in the same vector (pBBR1MCS-5::phaZa1+lonA) the mobilization rates was 54,26%±7,2, presenting a significant lower variation. Thus, it is believed that there should be an ideal proportion of PhaZa1 and LonA to promote a P3HB mobilization more efficient, in recombinant E. coli strains, compatible with a role of LonA as an activator of PhaZa1.