Characterization of a fitness island containing polyhydroxybutyrate genes in an Antarctic Pseudomonas strain

AYUB ND; PETTINARI MJ; MÉNDEZ BS; LÓPEZ NI

Universidad Nacional de Quilmes, Buenos Aires, Argentina.

Congreso; Tercer Congreso Argentino de Microbiología General (SAMIGE).; 2006

SAMIGE

Polyhydroxyalkanoates (PHAs) are carbon and energy storage compounds that are accumulated by bacteria under unfavorable conditions. Accumulation and degradation of PHAs endows bacteria with enhanced survival, competition abilities and stress tolerance increasing fitness in changing environments. Recently, we analyze the phaRBAC operon responsible for the synthesis of polyhydroxubutyrate (PHB) in Pseudomonas sp. 14-3, a strain isolated from Antarctic environment, which shows high stress resistance in association with high PHB accumulation. Due that PHB accumulation is an uncommon feature in Pseudomonas species and on the basis of physiologic and genetic studies of Pseudomonas sp. 14-3, we hypothesized that the high fitness associated to high PHB production found in this strain was due to the acquisition of foreign PHB genes. We also postulated by first time, the inclusion of these genes in a mobile element similar to genomic islands. The phaRBAC cluster from Pseudomonas sp. 14-3 was found within a large mobile genetic element (32,3 kb) that we termed PFI (Pseudomonas sp. 14-3 fitness island containing PHB genes) due to it involves genes that increase fitness of the recipient microbe. We identified 28 ORF in the PFI. Functional assignment was possible for 23 ORF. The PFI began with a phage integrase, followed by two ORF related with DNA transfer. ORF7, upstream of the PHB cluster, was a sodium/glutamate symporter. Downstream of PHB cluster and in the same direction, we found a complete Type I system protein secretion composed by 4 ORF. The right side of the PFI contained a high percent of mobile elements or proteins associated with them. Several proteins: integrase, ParA, TraF, ORF20, ORF27 (helicase) and ORF28 (nuclease) were highly similar to proteins found within genomic islands. The average PFI percent G+C content was 58.8% close to that found in the genus Pseudomonas but was not uniform. The heterogeneity within the region involving PHB genes was due to different %GC between phaRBC (57%) and phaA (67%) indicating that phaBAC is a mosaic operon .Phylogenetic trees for PHB proteins showed that PhaA protein of Pseudomonas sp. 14-3 was acquired by vertical inheritance. By contrast, PhaB and PhaC trees suggested that the corresponding genes are not native characteristics of Pseudomonas sp. 14-3. In previous works we analyzed the role of pha genes in bacterial survival and stress resistance. These results suggest the importance of horizontal gene transfer of pha genes as a mechanism of adaptability to changing environments.