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The nucleotide composition of key enzymes involved in medium-chain-length polyhydroxyalkanoates (mcl-PHA) synthesis was analyzed in two newly isolated strains of Pseudomonas. The isolated strains were tested for their abilities to synthesize polyhydroxyalkanoates using three different substrates as a carbon source: sodium octanoate, oleic acid, and sodium gluconate. Both analyzed strains were able to accumulate mcl-PHA in a range from 2.07 to 21.40%, which depended on the substrate used. Potential nitrogen-dependent regulation of mcl-PHA synthesis was analyzed by cell cultivation in nitrogen-limiting and non-limiting conditions. The analyzed strains demonstrated an incremental increase of mcl-PHAs in response to nitrogen starvation when oleic acid and sodium gluconate were applied as the carbon source. The transcriptional analysis showed that the induction of gene coding for PHA synthases was correlated with an increment in mcl-PHAs content. Both analyzed strains revealed differences in terms of the studied gene's expression, showing a dependence on the carbon source used.

The diversity of polyhydroxyalkanoates-producing bacteria in freshwater reservoirs in the Ecology Glacier foreland, Antarctica, was examined by a cultivation-dependent method. Isolated strains were analyzed phylogenetically by 16S rRNA gene sequencing, and classified as members of Alpha-, Beta-, or Gammaproteobacteria classes. Polymerase chain reaction was used to detect PHA synthase genes. Potential polyhydroxyalkanoates (PHAs) producers belonging mainly to Pseudomonas sp., and Janthinobacterium sp. were isolated from all five sampling sites, suggesting that PHA synthesis is a common bacterial feature at pioneer sites. All Pseudomonas strains had the genetic potential to synthesize medium-chain-length PHAs, whereas some isolated Janthinobacterium strains might produce short-chain-length PHAs or medium-chain-length PHAs. It is the first report revealing that Janthinobacterium species could have the potential to produce medium-chain-length PHAs.

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are biodegradable, biocompatible polyesters produced by many bacteria as intracellular storage compounds of energy and carbon. They have gained great attention as a new green alternative to petrochemical plastic such as polypropylene. The present study was focused on mcl-PHA production by two Pseudomonas strains (Gl01 and Gl06). To make this process more economical, waste rapeseed oil was used as a carbon source. The levels of PHAs synthesized by Pseudomonas sp. Gl01 strain and Gl06 strain were 21.0%, and 19.3% of CDW, respectively. The polyester accumulation increased until nitrogen and oxygen were depleted from the medium. Reverse transcription real-time PCR approach was applied to quantitatively evaluate phaC1, phaC2, and phaZ gene expression. A positive correlation was found between the cellular PHA content and the gene expression of the PHA synthases. The transcriptional analysis revealed that the phaC1 and phaZ genes could be co-transcribed. The overexpressed phaC2 gene was only observed in the Gl06 strain. The monomeric composition of the obtained mcl-PHA was dependent on the strain: 3-hydroxyoctanoic acid (3HO) and 3-hydroxydecanoic acid (3HD) were dominant in strain Gl01, whereas 3-hydroxyhexanoic (3HHx) was present in significant amounts in strain Gl06.Practical applications: This article presents the procedure of medium-chain-length polyhydroxyalkanoates (mcl-PHAs) synthesis by the Pseudomonas Gl01 and Gl06 strains from waste rapeseed oil as a feedstock. Beside the microbial production of these environmentally friendly plastics, this approach also represents a new way of utilizing waste oils. The knowledge of the key enzymes involved in mcl-PHAs accumulation is necessary in order to understand the mechanisms of their synthesis, and to use them effectively in biotechnological applications.