Hydroxy-fatty acid production in a Pseudomonas aeruginosa 42A2 PHA synthase mutant generated by directed mutagenesis

The treatment of oily wastewater by thermo-responsive calcium alginate capsules immobilized Pseudomonas aeruginosa

A microfluidic strategy of smart calcium alginate (CA) capsules is presented to immobilize Pseudomonas aeruginosa to treat oil slicks effectively. The capsule wall is embedded with poly (N-isopropyl acrylamide) sub-microspheres as thermo-responsive switches. CA capsules, with a diameter of 3.26 mm and a thin wall thickness about 12.8 μm, have satisfying monodispersity, cavity structure, and dense surface structures. The capsules possess excellent encapsulation of bacteria, which are fixed in a restricted space and become more aggregated. It overcomes the disadvantages of a long fermentation production cycle, easy loss of bacteria, and susceptibility to shear effect. The smart CA capsules immobilized with bacteria treat model wastewater containing soybean oil or diesel and display favorable fermentation ability. The capsules can effectively treat oil slicks with high concentration, and it is an economical way for processing oily wastewater. PRACTITIONER POINTS: A thermo-responsive calcium alginate capsule was prepared by microfluidic strategy. Pseudomonas aeruginosa is environmentally friendly in treating oil slicks. The capsules, immobilized bacteria, treat oil slicks effectively. This study provides an economical way for processing different oily water.

Enhanced rhamnolipid production in Burkholderia thailandensis transposon knockout strains deficient in polyhydroxyalkanoate (PHA) synthesis

Microbially produced rhamnolipids have significant commercial potential; however, the main bacterial producer, Pseudomonas aeruginosa, is an opportunistic human pathogen, which limits biotechnological exploitation. The non-pathogenic species Burkholderia thailandensis produces rhamnolipids; however, yield is relatively low. The aim of this study was to determine whether rhamnolipid production could be increased in Burkholderia thailandensis through mutation of genes responsible for the synthesis of the storage material polyhydroxyalkanoate (PHA), thereby increasing cellular resources for the production of rhamnolipids. Potential PHA target genes were identified in B. thailandensis through comparison with known function genes in Pseudomonas aeruginosa. Multiple knockout strains for the phbA, phbB and phbC genes were obtained and their growth characteristics and rhamnolipid and PHA production determined. The wild-type strain and an rhamnolipid (RL)-deficient strain were used as controls. Three knockout strains (ΔphbA1, ΔphbB1 and ΔphbC1) with the best enhancement of rhamnolipid production were selected for detailed study. ΔphbB1 produced the highest level of purified RL (3.78 g l⁻¹) compared to the wild-type strain (1.28 g l⁻¹). In ΔphbB1, the proportion of mono-rhamnolipid was also increased compared to the wild-type strain. The production of PHA was reduced by at least 80% in all three phb mutant strains, although never completely eliminated. These results suggest that, in contrast to Pseudomonas aeruginosa, knockout of the PHA synthesis pathway in Burkholderia thailandensis could be used to increase rhamnolipid production. The evidence of residual PHA production in the phb mutant strains suggests B. thailandensis possesses a secondary unelucidated PHA synthesis pathway.

Yield and kinetic constants estimation in the production of hydroxy fatty acids from oleic acid in a bioreactor by Pseudomonas aeruginosa 42A2

We modelled the production of hydroxy fatty acids from oleic acid by Pseudomonas aeruginosa 42A2 in a bioreactor with a non-dispersive aeration system. First, we designed an adapted wetted-wall gas-absorption column, offering a k La value of 39.9 h(-1), to enhance oxygen absorption in the culture media and prevent foam formation. Then, we analysed different kinetic models to simulate the yield coefficients and the kinetic constants in this bacterial transformation. Monod model fitting (μ max1 = 0.51 h(-1), K S1 = 1.60 C-mol l(-1), μ max2 = 0.12 h(-1), K S2 = 0.035 C-mol l(-1), and k 2 = 0.033 h(-1)) showed a good accuracy with the experimental data sets and was chosen for its simplicity. Lastly, mass balances were carried out to establish the stoichiometry of this biotransformation with the following yield coefficients, Υ X/OA, Υ X/(10S)-HPOME and Υ (10S)-HPOME/(7S10S)-HPOME of 0.172, 0.347 and 2.388 C-mol C-mol(-1), respectively.

Unveiling the genes responsible for the unique Pseudomonas aeruginosa oleate-diol synthase activity

Pseudomonas aeruginosa displays the ability to perform bioconversion of oleic acid into a class of hydroxylated fatty acids known as oxylipins. A diol synthase activity is responsible for such a conversion, which proceeds through the dioxygenation of oleic acid to release hydroperoxide 10-H(P)OME ((10S)-hydroxy-(8E)-octadecenoic acid), followed by conversion of the hydroperoxide intermediate into 7,10-DiHOME ((7S,10S)-dihydroxy-(8E)-octadecenoic acid), both of which accumulate in the culture supernatant. Several mutants of P. aeruginosa PAO1 were analyzed for the production of 10-H(P)OME and 7,10-DiHOME and two of them (ORFs PA2077 and PA2078), unable to release hydroxylated fatty acids, were detected and selected for further analysis. Involvement of ORFs PA2077 and PA2078 in oleate-diol synthase activity was confirmed, and their respective role in the conversion of oleic acid was analyzed by mutation complementation. Activity restoration revealed that gene PA2077 codes for the 10S-dioxygenase activity (10S-DOX) responsible for the first step of the reaction, whereas PA2078 encodes for the (7S,10S)-hydroperoxide diol synthase enzyme (7,10-DS) which allows the conversion of 10-H(P)OME into 7,10-DiHOME. Heterologous expression of both enzymes separately showed that no hetero-complex formation is required for enzymatic activity. Bioinformatics and RT-PCR analysis revealed that both genes constitute a new fine regulated oleate-diol synthase operon, originated by a gene duplication event followed by neofunctionalization for environmental adaptation, being unprecedented in prokaryotes.

Production of hydroxy fatty acids by microbial fatty acid-hydroxylation enzymes

Hydroxy fatty acids are widely used in chemical, food, and cosmetic industries as starting materials for the synthesis of polymers and as additives for the manufacture of lubricants, emulsifiers, and stabilizers. They have antibiotic, anti-inflammatory, and anticancer activities and therefore can be applied for medicinal uses. Microbial fatty acid-hydroxylation enzymes, including P450, lipoxygenase, hydratase, 12-hydroxylase, and diol synthase, synthesize regio-specific hydroxy fatty acids. In this article, microbial fatty acid-hydroxylation enzymes, with a focus on region-specificity and diversity, are summarized and the production of mono-, di-, and tri-hydroxy fatty acids is introduced. Finally, the production methods of regio-specific and diverse hydroxy fatty acids, such as gene screening, protein engineering, metabolic engineering, and combinatory biosynthesis, are suggested.

Production of long-chain hydroxy fatty acids by microbial conversion

Hydroxy fatty acids (HFAs) are very important chemicals for versatile applications in biodegradable polymer materials and cosmetic and pharmaceutical industries. They are difficult to be synthesized via chemical routes due to the inertness of the fatty acyl chain. In contrast, these fatty acids make up a major class of natural products widespread among bacteria, yeasts, and fungi. A number of microorganisms capable of producing HFAs from fatty acids or vegetable oils have been reported. Therefore, HFAs could be produced by biotechnological strategies, especially by microbial conversion processes. Microorganisms could oxidize fatty acids either at the terminal carbon or inside the acyl chain to produce various HFAs, including α-HFAs, β-HFAs, mid-position HFAs, ω-HFAs, di-HFAs, and tri-HFAs. The enzymes and their encoded genes responsible for the hydroxylation of the carbon chain have been identified and characterized during the past few years. The involved microbes and catalytic mechanisms for the production of different types of HFAs are systematically demonstrated in this review. It provides a better view of HFA biosynthesis and lays the foundation for further industrial production.