A metabolic engineering strategy for producing free fatty acids by the Yarrowia lipolytica yeast based on impairment of glycerol metabolism.

In recent years, bio-based production of free fatty acids from renewable resources has attracted attention for their potential as precursors for the production of biofuels and biochemicals. In this study, the oleaginous yeast Yarrowia lipolytica was engineered to produce free fatty acids by eliminating glycerol metabolism. Free fatty acid production was monitored under lipogenic conditions with glycerol as a limiting factor. Firstly, the strain W29 (Δgpd1), which is deficient in glycerol synthesis, was obtained. However, W29 (Δgpd1) showed decreased biomass accumulation and glucose consumption in lipogenic medium containing a limiting supply of glycerol. Analysis of substrate utilization from a mixture of glucose and glycerol by the parental strain W29 revealed that glycerol was metabolized first and glucose utilization was suppressed. Thus, the Δgpd1Δgut2 double mutant, which is deficient also in glycerol catabolism, was constructed. In this genetic background, growth was repressed by glycerol. Oleate toxicity was observed in the Δgpd1Δgut2Δpex10 triple mutant strain which is deficient additionally in peroxisome biogenesis. Consequently, two consecutive rounds of selection of spontaneous mutants were performed. A mutant released from growth repression by glycerol was able to produce 136.8 mg L-1 of free fatty acids in a test tube, whereas the wild type accumulated only 30.2 mg L-1 . Next, an isolated oleate-resistant strain produced 382.8 mg L-1 of free fatty acids. Finely, acyl-CoA carboxylase gene (ACC1) over-expression resulted to production of 1436.7 mg L-1 of free fatty acids. The addition of dodecane promoted free fatty acid secretion and enhanced the level of free fatty acids up to 2033.8 mg L-1 during test tube cultivation.

Methods coagulation/flocculation and flocculation with ballast agent for effective harvesting of microalgae.

The effects of coagulant (FeCl3·6H2O), various flocculants based on polyacrylamide (PAA), polyethylenoxide (PEO) and flocculated biomass as ballast agent, dosage and sedimental time on flocculation efficiency of harvesting Chlorella vulgaris GKV1 cultivated in a laboratory were investigated. The results of this work indicated that the flocculation efficiency achieved about 90% after 5 min of sedimentation when adding of coagulant and flocculant mixture (FeCl3 50 mg/l+PEO based Sibfloc-718 7.5 mg/l) or flocculant with ballast agent (Sibfloc-718 7.5 mg/l+10% flocculated biomass). PAA and PEO showed good flocculation efficiency at dosage of 0.025 and 0.015 g/l, respectively without pH adjustment. Finally, the most suitable flocculation method was discussed in this paper.